Antibiotics in animals: ACVIM consensus statement

Every year, the American College of Veterinary Internal Medicine (ACVIM) commissions "consensus statements" on specific topics. They’re developed by an expert panel, put up for review by ACVIM members (board certified veterinary internal medicine specialists), and published in the Journal of Veterinary Internal Medicine.

Hot off the (electronic) press is the 2015 ACVIM Consensus Statement on Therapeutic Antimicrobial Use in Animals and Antimicrobial Resistance. Assembled by an international group of experts in infectious diseases, microbiology, internal medicine and pharmacology, it’s an expansion on the highly regarded 2006 equivalent.

To download the consensus statement, click here.


Communication done right: EVH-1 in Minnesota

Two cases of EHV-1 have been detected on a farm in Prior Lake, Minnesota.  There aren't a lot of details about the cases, other than one horse was put down, and the other was taken to the University of Minnesota veterinary hospital for treatment and has apparently recovered and is ready to come home.

The barn is being monitored by the Minnesota Board of Animal Health for the next three weeks, which is the typical recommended quarantine period after the last case has either been removed or isolated from the rest of the animals.  Hopefully during this time the rest of the horses will get twice-daily temperature checks to ensure any other animals that may have been infected are detected and isolated as soon as possible.  Other routine infection control practices are hopefully also in place, such as hand hygiene between handling animals, and not sharing equipment between stalls and horses (particularly things like water/feed buckets, twitches, grooming supplies etc.).  These practices should be in place all the time, but they frequently get extra attention in outbreak situations.

The remarkable part about this case is what the stable owner did after the disease was diagnosed.  Instead of trying to keep it quiet or cover it up, she not only reported it to the Board of Health, but she also called everyone who visited the farm and the local veterinary hospitals, and even posted information on facebook to let everyone know what was going on.  Fantastic!  Part of the reason for being so proactive may be that the local horse expo last April was close to empty due to cases of EHV in the area affecteing 14 horses.  It is great to see someone reaching out like this to give the community a "heads up" so that others will keep a closer eye on their animals and hopefully prevent spread of the disease.  Hopefully she did it in an informative manner, and along with announcing the problem also told people about the plan to contain it.  It's always important to include the plan of action so the news itself doesn't incite panic.

Equine outbreaks...EHV-1, glanders

Two cases of fatal equine herpesvirus type I (EHV-1) neurological disease have been confirmed in the Dickinson, Texas, area. Three more recent deaths are suspected to be associated with the virus as well. The horses were from two boarding stables that are currently under quarantine, as is a veterinary clinic. As always, there’s a need for prudence and common sense in this situation. EHV-1 outbreaks are typically small and easily contained, but the right combination of bad luck and bad management can lead to widespread problems. The keys to containing an outbreak like this are prompt investigation to identify exposed horses, good communication, honesty (e.g. not hiding the fact that you have a sick or exposed horse), cooperation/compliance and basic infection control practices. So far, it sounds like none of the monitored horses have developed signs of infection and hopefully this one’s going to be done soon.

A more perplexing situation is the report of glanders (Burkholderia mallei infection) in a German horse. Glanders is a very serious disease in horses that can also be transmitted to people, and B. mallei is considered a potential bioterrorism agent. Glanders has been eradicated in many regions of the world, but some are concerned that eradication may be at risk. This case supports that concern since Germany hasn’t seen a case of glanders since 1955, and the affected horse in this case never left the country. The horse wasn’t sick, but it had serological (antibody) evidence of having been infected. Testing was only performed because the horse was being exported. Serological testing was repeated and was still positive, so the horse was euthanized. Glanders was subsequently confirmed through identification of bacterial DNA from skin scabs. None of the 30 other horses that were being monitored developed disease and all were negative on blood tests. The situation is considered "resolved," but with no source identified.  The OIE report concludes “It is known that the affected animal had never been moved outside of Germany. There might have been indirect contacts to South America. The source of infection is still unknown.”


EEE in Ontario 2014

2014 was the worst year ever for Eastern Equine Encephalitis (EEE) in Ontario (though our numbers still pale in comparison to more endemic areas in the southern US, such as Florida). A recent article published in the Animal Health Lab (AHL) Newletter (December 2014) by Dr. Alison Moore from OMAFRA sums things up well:

"Twenty-two horses and 2 emus in the province died or were euthanized due to the disease with potentially as many deaths being suspected by attending veterinarians. Two horses were confirmed infected but survived. Counties in Eastern Ontario suffered the greatest casualties. Diagnosis in 21 horses was by serum IgM ELISA testing and 3 were diagnosed by RT-PCR on brain tissue. The affected horses were diagnosed between the end of July and the end of October. Ages of affected horses ranged from 2-20+ years, with no breed or sex predilection. Most of the infected horses were unvaccinated backyard horses and only a single horse per property was clinically affected. Most horses had an acute onset of disease with death or euthanasia performed within 24-48 hours. Common clinical signs included ataxia progressing to recumbency, with fever noted in some and blindness and head pressing noted in others. In the 2 horses that survived, the clinical signs were mild (ataxia and lethargy). The 2 emus were diagnosed with hemorrhagic enteritis and EEEV confirmed in the intestine and liver by RT-PCR.

The virus causing EEE is transmitted by mosquitoes. In Ontario, the most important species is Culiseta melanura, which feeds on birds. Bridge vectors, mosquitoes that feed on both birds and mammals, then complete the cycle to humans and horses. Outbreaks occur in hardwood, flooded areas with competent avian reservoirs and mammals present. Horses and humans are dead-end hosts as they do not produce sufficient viremia to infect mosquitoes.

So why was 2014 such a devastating year? Some speculate that eastern Ontario was relatively warmer this year than other parts of the province, others say it was due to the amount of spring precipitation. Others implicate the spring migration of wading birds such as herons from Florida. Herons are a preferred host for Culiseta sp. over winter in Florida, a major reservoir state for EEEV. The spring migration of herons and similar birds is thought to disseminate the virus to the northern USA and Canada. OMAFRA and Public Health Ontario will be working together over the winter to determine any associations between ecological and meteorological factors and disease occurrence."

Given the amount of activity we saw with this virus this past summer, vaccination of horses against EEE (particularly in hard-hit areas) will be important come spring to help avoid a repeat of this year's outbreak.

More information about the occurrence of EEE and other equine neurologic diseases in Ontario is available on the OMAFRA website: Equine Neurological Disease Surveillance 2014.

2013 US rabies recap

It’s that time of year. No, not for snow (although it is snowing here at the moment). It’s time for the annual US rabies surveillance report in the Journal of the American Veterinary Medical Association (Dyer et al. Rabies surveillance in the United States during 2013).

The highlights…

  • Over 5800 rabid animals were identified in the US. 92% of those were wildlife. That’s going to be a profound underestimation since most rabid wildlife aren’t caught and tested, but it shows that rabies is still alive and well in the US.
  • Rabies was most commonly diagnosed in raccoons, followed by bats, skunks and foxes.
  • Among domestic animals, there were 247 cats, 89 dogs, 86 cattle, 31 horses/mules, 9 sheep/goats, 3 pigs, 2 llamas, and a partridge in a pear tree. (Obviously the last one’s my lame attempt at early winter humour. Birds aren’t a rabies concern).
  • Other species affected included mongooses (38; as always, just from Puerto Rico), groundhogs (37), bobcats (16), coyotes (5), deer (5), otters (3), opossums (2), wolves (2), marmots (2), a rabbit and a fisher. Most of those are fairly typical, both in terms of the species affected and the numbers. 
  • Pennsylvania had the most rabid cats, while Texas won for most rabid dogs.
  • Vaccination history was not usually available for rabid dogs and cats. None of the rabid cats had been properly vaccinated against rabies. One of the rabid dogs had been vaccinated, a 10-month-old dog that developed rabies 7 months after receiving its first dose. This one’s a bit concerning, though. By being vaccinated at 3 months of age, it would have been considered "up-to-date" on rabies vaccination and this would therefore be a vaccine failure. No vaccine is 100% effective (although rabies vaccine is considered very effective as vaccines go) and the dog having only received only one dose because of its age was probably a key factor. 
  • The dominant rabies virus variants had a typical geographic distribution (see map above).

Three people were diagnosed with rabies during the year.

  • The first was a person who died of raccoon rabies. There was no history of animal exposure, but he had received a kidney transplant 17 months earlier. The donor had been diagnosed with severe gastroenteritis, but also had some neurological abnormalities and when banked samples from the donor were tested, rabies virus was found. Three other organ recipients were then given post-exposure prophylaxis.
  • The second person was a man from Guatemala who was detained trying to enter the US. While in custody, he developed neurological disease and died. Central American canine rabies variant was identified.
  • I assume the third reported case was the organ donor from the first case, since the case was diagnosed in 2013 (even though the person died in a different year).

As per usual, there’s a little information about Canada and Mexico in the paper.

  • 116 rabid animals were identified in Canada, 88% of those being wildlife. There were also 12 cats and dogs (combined) and 2 horses.
  • In Mexico, an important finding was the fact that, for the first time since 1938, no people died of rabies. Eleven rabid dogs were identified. However, care must be taken in comparing data from different countries because of potential differences in testing (if you don’t look too hard, you don’t find).


Never a simple story: West Nile in California

Orange County CA is currently experiencing a major outbreak of West Nile infection in people. Since January 94 cases have been confirmed, three of which were fatal, representing nearly a quarter of the 400 cases reported across the country so far this year. The number of cases of infection with a mosquito-borne virus like West Nile (or EEE, which we’ve been seeing over the last month in Ontario horses) can be affected by a lot of factors, including climate/weather, flooding or drought, bird populations and movements, mosquito populations and local mosquito species, and population density of those affected, be they people or animals.

Often we associated wet weather and flooding with increased incidence of diseases like West Nile, but this year California is experiencing a drought. How does that make sense? It’s been suggested that the dry weather is driving birds into more populated areas to look for water. More infected birds in the area provides more opportunity for mosquitoes to bite the birds and then transmit the virus to a person. The number of mosquito pools testing positive in Orange County (80%) is the highest its been since West Nile first hit California a decade ago, and 6.5 times more dead birds (260 total) have tested positive for WNV compared to 2013.

Most of the human cases in California included some signs of illness. When you consider that 80% of people infected with WNV show no signs of the disease, that means there has actually been an even larger number of people actually infected.

The impact on the local horse population has not been mentioned, but it is unlikely that horses will escape this outbreak unscathed. After a relatively slow year for WNV in 2013, I wonder how many horse owners in the area may have decided to forgo vaccinating their horses this year, and may now be regretting it. It’s easy for us to get complacent about infection control when things are going well. In the case of West Nile, people may stop taking precautions to avoid mosquitoes, to remove standing water from their property, and vaccinating their horses. It’s important to remain vigilant though, because there are so many different factors involved in the cycles of various diseases that predicting their resurgence can be extremely difficult, if not impossible. Taking some simple preventative steps, and making basic infection control practices habit can help reduce the impact of unexpected outbreaks, and help keep everyone (people and animals) healthier and safer.

EEE alert, Ontario

The Ontario Ministry of Agriculture Food and Rural Affairs (OMAFRA) has issued an Equine Health Advisory in response to diagnosis of Eastern Equine Encephalitis (EEE) in a horse in Stormont/Dundas/Glengarry, in eastern Ontario. The 12-year-old gelding died, which is the typically outcome with this disease in horses.

EEE is a devastating but fortunately rare (at least in Ontario) disease of horses, people and an assortment of other species (including emus, llamas and alpacas). Typically, a few equine cases are identified in Ontario every year, with human cases being rarer. However, since people and horses are infected in the same way - by the bite of an infected mosquito - finding the disease in a horse indicates risk to both horses and humans in the region.

More information about EEE cases in North America can be found at WormsAndGermsMap.  Information for horse owners in Ontario, as well as Ontario-only equine neurological disease cases, can be found on the OMAFRA website.

St. Louis encephalitis in a horse

Hopefully we can chalk this one up on the "weird and not-so-wonderful" list, and not have it emerge as a significant problem. However, there’s something new to pay attention to as St. Louis Encephalitis virus (SLEV) infection was recently identified in a Brazilian horse with neurological clinical signs.

SLEV is a Flavivirus and a relative of some other important viruses such as West Nile virus and Dengue virus. Like its relatives, SLEV is transmitted by mosquitoes.

In a recent paper (Rosa et al. 2013), SLEV was found in the brain of a horse from Minas Gerais, Brazil that had died of neurological disease. Fairly extensive testing was performed to rule out other causes, so the presence of the virus in the brain and the absence of other potential causes is quite suggestive that SLEV was the problem here. It’s an interesting finding because while this virus is widespread in North and South America, from Canada to Argentina, it rarely causes disease in mammals. It circulates between birds via mosquitoes and occasionally spills over into mammals, which are considered "accidental" and "dead end" hosts since they are not part of the virus's normal transmission cycle and once infected, they can’t pass the virus on to anyone/anything else. Most infections are reported in people and they tend to be mild, although serious neurological disease can occur, especially in elderly individuals.

So, this would be the first confirmed report of SLEV-associated disease in a horse. The signs of disease were pretty non-specific and included depression, incoordination and paralysis of the hind limbs. That’s something we can see with a few different neurological diseases in horses, including the much more common EHV-1 encephalomyelopathy (and in Ontario and other parts of North America, West Nile virus).

The infection was diagnosed in a horse that died in 2009 after 72 hours of neurological disease. That’s a long time from disease to diagnosis, but in this case it’s probably also a good sign. No other horses on the farm were affected at the time, and no one has reported changes in neurological disease patterns in the area (or beyond) since then; therefore, this presumably was not the start of a large, rapidly moving new disease, as we saw when West Nile virus hit North America in the early 2000s.

Hopefully this was just a strange one-off infection, but it shows the need for continued infectious disease surveillance and the ever-changing challenges of infectious diseases.

Traveling with your horse...infection control considerations

It's not a coincidence that we see more equine infectious diseases during busy show seasons. Shows are a great way for infectious diseases to spread, with outcomes ranging from disease in single horses to widely disseminated outbreaks, even across international borders.

We can't eliminate all risk in life, and the risk of infection in horses is no different, but we can do many things to reduce the risk. A lot of these are what I call "low hanging fruit," meaning they are measures that are really quite easy and practical (but often not done regardless).

Friend and colleague Dr. Paul Morley and his team have put together a great 7-minute video entitled "Preventing infections in Horses Attending Shows and Traveling." It provides great information and is well presented, and anyone who travels with horses (or runs a farm that has horses that travel) should take a look.

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West Nile virus in Colorado

It's that time of year again... at least in some areas.

West Nile virus (WNV) infection has been identified in a horse in Colorado. It's not really a surprise. West Nile virus is one of those pathogens that we know is coming back every year, we just don't know exactly when. The date of return varies a bit from year to year, but tends to be fairly consistent within a region (e.g. if West Nile cases started to crop up in a certain state in mid-August last year, they are likely to start again at roughly the same time this year).

The timing of onset of WNV cases depends on a few things, including WNV circulation in birds, climate and mosquito populations. The latter is quite important since only certain mosquitoes like to bite both birds and mammals. These particular mosquitoes species (called bridging vectors) are the concern, since they are more likely to bite an infected bird, and then possibly transmit the virus to a horse (or human) if they bite them next. Mosquito populations aren't the same all year and in all regions, which explains in part why WNV cases don't start earlier in the year, and why there are some major regional variations in disease despite the widespread presence of mosquitoes.

In Ontario, I suspect we have a few more weeks before we get the first reports of cases for 2014, but the WNV season is approaching here as well.

Photo credit: Rennett Stowe (click image for source)

Strangles and psychology

A couple days ago, I was talking to a vet who's trying to manage a strangles outbreak on a farm. In many outbreaks, the biggest hassles are dealing with horse owners, not the disease itself. Strangles, infection by the bacterium Streptococcus equi subsp. equi, is a highly contagious disease but one that is relatively easy to control if things are done right.

The critical variable is whether people will do things right.

There are many issues that result in prolonged outbreaks at single facilities or spread of strangles from farm to farms, but two are quite common, recurrent problems.

1. Unwillingness of people to skip shows during the outbreak. I understand the desire to go to shows, since the show season may be short and shows are what people look forward to all year. However, despite the fact that it's clearly unethical for people to take a horse to a show from a barn where a strangles outbreak is underway, it happens all the time. That's probably one of the most important ways strangles is spread during the show season.

2. People moving horses to other barns. It's not uncommon for there to have already been one or more people flee the barn by the time I'm involved in an outbreak investigation, and I've seen multiple situations where one-farm outbreaks have turned into regional outbreaks because of this. This response is sometimes because individuals want to try to avoid the outbreak (although their horse may have already been exposed, making it too late), or to avoid any restrictions that might be put on the barn and movement of horses therefrom.

Both situations are common, but ethically are unacceptable. If a person knows that his/her horse is on a farm where strangles is present, the animal is considered infectious until proven otherwise.

How can these problems be prevented?

1) Boarding contracts that stipulate owners will stay on the farm in the event of an outbreak (maybe not easy to enforce, but at least addresses the issue up front).

2) The carrot: Emphasizing that with a good infection control response, if a particular horse has not been exposed, it probably won't be, and if it has been exposed, it's a risk to others. Either way, keeping it on the farm is the best for it and for others.

3) The stick: Reminding owners that they know their horses might have been exposed to strangles. If they take a horse somewhere and infect other horses, they might be (or should be) liable for any costs and losses associated with those subsequent cases. Infectious diseases are an inherent risk of life and are not always preventable, but when someone knowingly creates a high risk situation (and that situation was avoidable), legal consequences may ensue.

Image credit: Jebulon (click image for source)

Vesicular stomatitis in Texan horses

Hint... if you like time off during the summer, don't get into equine infectious diseases.

Vesicular stomatitis (VS) has been identified in five (so far - probably more to come) horses in Kinney County, Texas. The case is shown on the Worms & Germs Map, and more details are available in the news release from the Texas Animal Health Commission.

Vesicular stomatitis is a viral disease that causes blistering and sores of the mouth/muzzle of infected animals, as well as on the udder and coronary band (around the hooves) in some cases.  The disease is certainly uncomfortable, and can cause animals to stop eating, but the lesions gradually heal and the infection resolves on its own in a few weeks.  Part of the reason VS is such a big deal is because it can also infect cattle, sheep, goats and pigs, and in these species the lesions look just like those caused by Foot and Mouth Disease, which is a very serious foreign animal disease to Canada and the US.

Rabies confusion and clarification: Ontario

Following the Canadian Food Inspection Agency's (rather mind-boggling) abandonment of the rabies response portfolio, there's been a scramble by provinces to figure out what to do. The CFIA will still perform testing, but will not have any role in sample collection, sample shipping or investigation. I'm not sure what most provinces are doing (and based on the calls I get from people in different provinces, I'm not alone) but in Ontario, a lot of effort has been put into working out a new system. Ontario's Ministries of Health and Long-Term Care (MOHLTC) and Agriculture and Food (OMAF) have taken on different components of the void left by CFIA. A lot of work has gone into this transition, but there's still a lot of confusion (and some misinformation).

Click here for a useful summary for veterinarians on the current situation, as provided by OMAF.

Rabies three ways

Not many days go by when I don’t get a few calls about rabies. Here are a couple from yesterday that highlight some important issues.

An indoor cat tangled with a bat. The bat’s no longer around to test so this is considered a potential rabies exposure (bats being important rabies vectors, and catching and snacking on a bat being a potential way to encounter the virus). Unfortunately, the cat was not vaccinated against rabies, meaning it needs a strict 6 month quarantine, or euthanasia. A cheap and easy rabies vaccination would have significantly reduced the issue, changing that to a 45 day observation period, and greatly decreasing the risk that the cat would develop rabies. Indoor cats need to be vaccinated. Even if the cat never goes outside, rabies virus can find its way inside (and the number of indoor cats that get into fights with wildlife or hit by cars indicates that indoor cats aren’t always indoors!). I have personal experience with that.

A horse in Texas was diagnosed with rabies. Rabies is uncommon in horses but it certainly occurs. As above, rabies vaccination is cheap insurance. No vaccine guarantees protection but it’s a very effective vaccine, a fatal disease, and horses with rabies have attacked and killed people. Every horse (in or traveling to any rabies-endemic country) should be vaccinated against rabies.

Additionally, various (continuous) reports of rabies deaths in India also highlight the importance of controlling rabies at the population level, to reduce the risk of exposure by reducing the number of rabid animals.  There is also an absolutely critical need for healthcare providers to properly handle potential rabies exposures.

The Texas rabies case can be found on Worms & Germs Map (, along with some other recent cases.

EEE in Florida horse

It's hard to think about mosquito-borne disease season here at the moment, with temperatures in Ontario still going down to freezing, but the highly concerning disease eastern equine encephalitis (EEE) has been identified in a Marion County, Florida horse. This mosquito-borne virus causes highly fatal infection in both humans and horses. People don't get it from horses, though - rather, people are exposed the same way horses are, by a bite from an infected mosquito.

Mosquito borne diseases vary quite a bit geographically, both in terms of where and when they occur. EEE is fortunately very rare around here, but it's a bigger concern in other areas, particularly the southeastern US and US seaboard.

We won't likely see mosquito borne diseases like EEE and West Nile virus infection in Ontario for a few months, but in other areas, the risk period has already begun. Knowing what diseases occur in your area, what diseases occur in areas your horse may visit, and when those diseases occur is important. That's one of the reasons we recently launched the Worms & Germs Map. The location of the EEE case mentioned here can be found on that site.

Equine herpesvirus 1 at Aqueduct

Spring’s slow arrival has brought many things. Disappearing snow, a hint of green in the grass... and a greater risk of disease outbreaks in horses. Outbreaks can occur at any time of year but we often start to see certain infectious diseases ramp up as horses start moving around more at the start of training, racing and showing seasons.

A tentative diagnosis equine herpesvirus I (EHV-1) neurological disease in a horse has resulted in a precautionary quarantine of a barn at Aqueduct racetrack in New York. This virus is a concern because of the potential for serious disease (e.g. the affected horse died) and the potential for large outbreaks. However, concern needs to be tempered by awareness that this virus is widespread in the horse population and that single, sporadic infections are more common than outbreaks.

At Aqueduct, horses in the barn in which the affected horse was housed are not permitted to race, and may only train after the general horse population is off the track. Rectal temperatures of horses from that barn are being checked twice a day to help detect any new cases as soon as possible. Usually, this type of outbreak response goes on for 21-28 days after the last identified case, but the planned time frame hasn’t been stated here.

Too often, we see one of two things happen when EHV-1 is identified. Traditionally, little was done in the hope that nothing bad would happen. More recently, the pendulum has swung the other direction and people often completely freak out over it, panicking and implementing measures that are over the top.

Like most things, a happy medium is needed, with enough attention (and common sense practices) to reduce the risk of further cases, while no causing undue hardship to those affected. It’s not always an easy balance to find. As someone who is frequently involved in these situations, it’s tough to figure out where to draw that line, especially when you have multiple different agendas, perceptions and degrees of risk tolerance. Taking a draconian approach (lock all the horses in the barn until further notice) is the easy way out, but it rarely makes sense. Being more balanced and less restrictive creates some risk for people making those decisions (because if something bad happens, they’re probably going to be blamed) but the easy-way-out is rarely the best-way-out.

The response at Aqueduct seems to be well balanced.

  • They’ve identified a potential problem.
  • They’re trying to determine if there are more cases (although I’d take temperatures of all horses on the track, not just that barn. You need to know if it’s escaped from the index barn.)
  • They’re communicating.
  • They are taking reasonable measures with the highest risk group (horses from the affected barn).
  • They’re not taking the easy, knee-jerk response of totally restricting horses in that barn, rather they are using common sense practices to limit the risk of further exposure should any other horses in the barn be affected.

Most often, these incidents end up being single cases. However, by the time you realize something is going on, it’s possible that multiple horses have already been infected and are getting ready to become sick and/or be able to transmit the virus further. A short period of relatively aggressive but reasonable precautions is usually the key in outbreak management, and hopefully nothing more will come from this.

The location of this outbreak can be seen on the Worms & Germs Map at

EHV-1 in the news

There have been a few reports of equine herpesvirus (EHV-1) neurological disease over the last couple of weeks and some other cases that have been less well publicized. Hopefully it’s all just been a blip on the radar and not a sign of things to come as equine events start to ramp up at this time of year. However, it would be good for racetracks to take these cases as reminders of the ever-present risk of EHV and the need to try to prevent problems.

Some tracks have taken this issue seriously and are working on infection control and outbreak response plans. In response to one outbreak, a Minnesota track is building an isolation area for infected horses and implementing a variety of infection control measures.

Too often, the response to EHV-1 is only reactive: when there's no immediate problem, people don’t do anything, and when there is a problem, people freak out (and it’s hard to do things right when people are freaking out).

We need a happy middle ground that includes a reasonable response plan (effective and realistic) and proactive measures to both reduce the risk of an outbreak and to facilitate response.

Racetracks are starting to understand the need, although the response is variable. The number of outbreaks and the potential implications of them (e.g. sick or dead horses, cancelled racing, horses banned from going to certain tracks) means that it is in the horse owners’ and tracks’ best interests to do things right. What constitutes "right" is a moving target, though, and some people just don’t want to bother.

You can virtually guarantee that there will be EHV-1 outbreaks at racetracks this summer. A limited number of horses will die but there will be massive disruption based on quarantines (sometimes reasonable, often excessive) and other fall-out.

While there’s no way to completely eliminate the risk of EHV in horses, there are many things that can be done to reduce the risk of an outbreak. Some are relatively cheap and easy, such as

  • Ensuring that horses with signs consistent with EHV-1 are promptly examined and isolated
  • Avoiding shipping horses from sales directly into racing barns
  • Cohorting groups on tracks as much as possible to contain incidents to individual barns
  • Fostering routine infection control practices by people who frequently move between barns like veterinarians, farriers and riders/drivers

Other measures may take more time, effort and planning, such as creation of isolation areas and development of clear outbreak response plans. One of the most important things that can be done, however, is improving communication and trust. Often the biggest challenges in outbreaks involve poor communications, such as unwillingness to report cases, egos and agendas that get in the way of effective and timely response, and various other related problems that can be fixed by people thinking and talking to each other.

Some tracks are doing a good job of thinking proactively. Many are taking the "head-in-the-sand" approach. Any track could run into a problem, but my money’s on bigger problems occurring at the tracks that don’t take this problem seriously.

Unfortunately, we’ll be talking more about EHV-1 outbreaks this summer.

Strangles and liability

Surprisingly (at least to me), I don't hear much about individuals suing other people because of infectious diseases in their horses (apart from sporadic situations involving veterinary hospitals). I'm not saying the increasingly litigious nature of society is a good thing, but I can see how lawsuits could happen given the costs associated with infectious diseases, the emotions that can be involved and the lack of a well-defined standard of care.

The potential for liability isn't necessarily a bad thing IF it motivates people to do what's right. While ideally it wouldn't take the threat of financial loss to properly motivate someone, it can be a useful argument. Our first strangles poster touched on social influences as a motivator (i.e. if you do something that causes other peoples' horses to get sick, you're not going to be popular). Our second poster (below) addresses the potential for liability, which I think is particularly real when people knowingly move horses from a farm with strangles, especially when they don't notify the new farm about the potential for strangles exposure and take appropriate precautions.

EHV-1 on Oregon farm

An outbreak of equine herpesvirus type 1 (EHV-1) neurological disease has occurred on an Oregon farm. At last report, five horses had tested positive for the virus (though it's not clear if all of them had neurological disease) and one had died.

EHV-1 outbreaks are not exactly rare these days. There's certainly more reporting of sporadic disease and outbreaks, but it also seems like there's been a true increase in outbreaks over the past 10-15 years. During my residency, we saw EHV-1 neuro cases not uncommonly, but almost always as single cases. Now, clusters like this are more common, for no clear reason.

Anyway, this outbreak appears to be contained, and it's good that there's been no movement on or off the farm in a while. This will likely end up being a sporadic, contained cluster on a farm with no broader implications. Since EHV-1 is very common, being found in the majority of horses, there's always some risk of disease occurring.  That's one of the main challenges we have in understanding and controlling this virus.

Tracking of EHV-1, and other equine (and dog and cat) diseases will soon be available on Worms & Germs MAP.  Stay tuned.

Strangles in the news

There's been a lot of press about strangles (Streptococcus equi) outbreaks in Ontario lately, including a biosecurity update from the Ontario Ministry of Agriculture and Food (OMAF). In some ways, it's surprising since this is an endemic disease and strangles is pretty much always causing trouble somewhere in the province. However, a little press is never a bad thing, if it can help get people to do what they need to do (but often don't do) to control this highly contagious equine disease.

A big problem with strangles control is the unwillingness of some people to admit they have cases and/or people knowingly taking exposed horses off the farm, thereby spreading the bacterium to other farms.

Along that line, here's our latest educational poster. As with all of our materials, feel free to print, copy, post or disseminate at will. A higher resolution version can be downloaded from the Worms & Germs Resources  - Horses page.

Animal Health Laboratory Zoonotic Diseases Report

The University of Guelph’s Animal Health Laboratory recently published a summary of selected zoonotic disease diagnoses in its monthly newsletter. It’s an interesting summary of what’s gone through the lab in the last year.  It also helps to remind us of the zoonotic potential of all of these pathogens, some of which are relatively common and can be found in a variety of species.

Equine neuro herpesvirus outbreak, New Zealand

An outbreak of equine herpesvirus type 1 (EHV-1) neurological disease (also known as equine herpes myeloencephalopathy (EHM)) is underway in a currently undisclosed location in New Zealand. It appears that at least 12 horses have been affected with 6 deaths, all on one farm.

This is being described as the first outbreak of the neurological form of EHV-1 in New Zealand. That's pretty surprising to me, since this virus in endemic in the horse population throughout the world, and although the neurological form of disease is sporadic it's certainly not a rare occurrence. I imagine there have been periodic cases and maybe small clusters, but perhaps they mean that this is the first large outbreak to be identified (but that’s a guess). We do seem to be seeing more large EHV-1 neurological outbreaks in recent years, and I don't think it’s just because we're recognizing them more.

Fortunately, there is now much more willingness amongst most sectors of the equine industry to take these outbreaks seriously and act much more quickly and comprehensively than in the past (when getting people to admit to an outbreak was a challenge, let alone getting any action).

Hopefully this one's been contained on the farm and no further spread will be encountered.

Stay tuned for the launch of WormsAndGermsMap, a real-time disease mapping site to track cases like this. Coming soon.

(click image for source)

Rabies in upstate New York horse

Rabies in horses is pretty rare but far from unheard of, and each case should be a reminder of the need for proper vaccination. The latest US case was a horse in Newport, New York, but I haven’t yet been able to track down more details. Presumably, human and animal contacts are being investigated, with assessment being made as to whether there was potential exposure to rabies virus. For people, that would mean a course of post-exposure prophylaxis. For animals, that would mean a quarantine, observation period or euthanasia, depending on the species and vaccination status.

The risk to people is quite low. The biggest human health risk is from being attacked or otherwise physically injured by a neurological horse, as opposed to getting rabies from an infected horse. But rabies is something with which we don’t play around, so anyone deemed to have been exposed will presumably be treated.

Rabies isn’t common in horses but it kills. Vaccinate your horses (and other animals).


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Equine Infectious Anemia: New info sheet

Although at times it may seem that winter is never-ending in parts of Canada, spring is actually only a couple of months away.  Along with spring comes insect season, and along with insects comes more than a few viruses.  One of these is the virus that causes equine infectious anemia (EIA).  This pathogen is a retrovirus like the human immunodeficiency virus (HIV), but EIA only affects equids (e.g. horses, donkeys, mules).  It's a very serious concern in the horse world, because horses become infected for life, and in Canada we have strict control measures to help prevent the spread of EIA into and within the country.  Nonetheless, in 2013 cases were detected on numerous premises in BC, Alberta and Saskatchewan.  Maps of the areas affected are available of the website of the Canadian Food Inspection Agency (CFIA).

To help horse owners understand more about this disease, the existing control program and the reasons behind it, as well as how they can help prevent the spread of EIA, we've created two new info sheets in collaboration with Equine Guelph and Equine Canada: a full-length version complete with references (9 pages) and a shorter summary version (4 pages).  Both versions are now freely available for download from the Worms & Germs Resources - Horses page, along with our many other equine infectious disease info sheets.

Rabid horse attacks owner

I've had the occasional debate with people about the public health risks of rabies in horses.

On one hand...

  • Rabies is rare in horses.
  • I've never seen a report of rabies transmission from a horse to a person.

On the other hand...

  • Rabid horses have attacked (and killed people).
  • It doesn't matter whether the horse gave you rabies or stomped on you. Dead is dead.

A Carroll County, Georgia horse owner learned the risk of rabid horses the hard way, but fortunately doesn't appear to have been seriously injured. .

One day, the owner was bitten while getting the horse out of the pasture.

The next day, the horse attacked him....and according to the owner, tried to kill him. That night, the horse was in the pasture chewing on its leg and periodically nosing the electric fence.

While rabies is rare, these are some of the hallmarks...aggression and strange behavior. The horse was euthanized and tested positive for rabies. Presumably, the owner is undergoing rabies post-exposure prophylaxis.

Rabies is nothing to play around with. It's very rare in horses but endemic in wildlife so there's always a chance for exposure in most regions. Rabies vaccination is a cheap and highly effective way to reduce the risk.

Eastern Equine Encephalitis alert: Ontario

'Tis the season...

Eastern equine encephalitis (EEE) is a very serious disease that's fortunately rare in Ontario, but when it happens, it's bad news. It's a viral disease transmitted by mosquitoes (similar to West Nile virus), and we often see a couple of horses affected every year, usually starting around now (late August) and extending into the fall.

The Ontario Ministry of Agriculture and Food has issued an alert after diagnosis of EEE in a 11 year old horse in Simcoe county (other cases have been reported in this area in previous years as well). They say the horse is recovering, which is a bit of a surprise because mortality rates with EEE are very high, and most affected horses die quickly.

What does this mean for horses in Ontario?

Not a lot, since we know EEE crops up every fall, and there's always some degree of risk, but it's a good reminder that this disease is a concern particularly at this time of year. The risk here isn't anywhere near the level it is in some US states, and with only a handful of cases every year (4 last year), the disease's overall impact in Ontario is low. However, infection is typically fatal and therefore not something to be ignored. A vaccine against EEE is available for horses, and it's been debated whether it should be a core vaccine for horses in Ontario. On one hand, the disease is typically deadly. On the other hand, it affects between 0 and a few horses every year, which is not many in the grand scheme of things (but if it's your horse, you don't really care about the "grand scheme" at that point).

What does it mean for people in Ontario?

Despite the name, EEE can affect people too. It's rare, but like in horses, it's devastating. There has never been a confirmed human case in the province, but they do happen  Earlier this month an elderly woman in Norfolk County, Massachusetts was diagnosed with and died from EEE (like Ontario, Massachusetts typically sees a few cases in horses every year as well). Humans and horses get infected the same way (a bite from an infected mosquito), so cases in horses mean there is EEE in mosquitoes in the area. There's no vaccine for people, so we're left with mosquito avoidance.

This is one of those "pay attention but don't panic" diseases.

Equine flu at Hastings BC racetrack

Hastings Racecourse cancelled racing last Saturday because of an outbreak of equine influenza in horses at the track. A recent CBC news report indicates that things started a week and a half earlier, with 150 horses affected when the race cancellations were announced. That's a pretty impressive outbreak.

There's no information about the response, beyond cancelling racing. In some ways, flu is quite easy to control because animals do not become long-term carriers of the virus and infected horses only shed the virus for a short period of time. This makes it easier to contain an outbreak with good infection control precautions, since you only need to implement them over a fairly short period of time. However, the downside is flu is highly infectious and can spread easily and quickly.

I have no first hand knowledge of this outbreak so I can't say anything about what was done or what was missed. However, from a generic standpoint, these are the main problems I see with this kind of outbreak.

There's no response.

  • This is too often the problem. This can occur because people don't realize something is happening or the snow-balling of issues that can result. Education is needed to help prevent this.
  • Lack of response can also occur because people don't want to tell anyone about an infectious case or don't trust the authorities. This sometimes happens if horsemen are worried about being stigmatized or prevented from racing or showing. Again, education is needed.
  • Sometimes, there's mistrust of track or regulatory personnel. If people are worried that the other group doesn't understand or care about their situation, or they don't realize the benefit of communicating, they might try to hide a problem.

There's a late response.

  • Another common problem. This usually occurs because people try the "I hope it will go away" approach to infection control first. This rarely works.
  • If you get infection control measures in place early, you can contain things much more easily. You're much more likely to contain an outbreak if you only have one horse, or a few horses, affected. It's also easier to contain the disease if you can keep it localized to one barn. Once it spreads to many horses and gets into multiple barns, it can be tough to stop.
  • This is why protocols that require reporting of fevers other other basic, early signs of infectious disease (and how to respond to them) should be commonplace.

The response is half-hearted.

  • Yet another common problem. Even when people get moving and try to contain an outbreak, it's often not done effectively.
  • One reason for this lack of efficacy is people often don't want to do what's recommended. Infection control measures always make life more difficult, and they take time, no doubt. They're important though. Skipping important measures and just trying to do the more convenient ones isn't a good response.
  • Another reason for an inffective response is not knowing what to do. Sometimes, I get involved in outbreaks after there's been an initial response and see lots of effort being put into relatively (or completely) useless activities, while the key control measures are ignored. Getting the input of experts as early as possible is critical.

There's inconsistent response.

  • This may be similar to 'half-hearted," but by this I mean an outbreak where some people do everything right, and some do little or nothing. Sometimes this is a result of poor communication, and therefore everyone doesn't understand what's happening. Better communication and education can help.
  • Other times, this can be caused by simple belligerence: "I don't want to do it so I'm not going to do it!" Sometimes good communication and education can help with this too, by showing people that it's to their own benefit. However, willful neglect is not uncommon and it's hard to handle.

The common themes to preventing these issues are communication and education.

More Ontario equine herpesvirus

An outbreak of equine herpesvirus type 1 (EHV-1) has resulted in implementation of a quarantine at Woodbine, a major Thoroughbred track in Toronto. This outbreak is unrelated to the recent outbreak at an Ontario Standardbred training facility.

The Ontario Racing Commission has issued the following release:

The Ontario Racing Commission (ORC) announced that there have been five confirmed reports of the neurotrophic form of EHV-1 in thoroughbreds residing in Barn 1 at Woodbine Racetrack. One horse was euthanized on June 10 after becoming recumbent with a fever. A second horse in the same barn (Barn 1) also had a fever and showed neurological signs. The second horse was transported to the Ontario Veterinary College for further evaluation and treatment.

Thoroughbred racing will continue at Woodbine. However, due to the infectious nature of this disease, the ORC has ordered the implementation of various infectious disease protocols to protect our equine athletes.

Effective immediately:

In order to determine any further spread of the disease to horses in other barns, no horses are to exit Woodbine Racetrack without ORC approval for the next 7 days (June 19). This restriction may be reviewed based on the progression of the disease.

In addition, no horse is allowed in or out of Barn 1 or Barn 3 for the next 7 days, including training. This restriction may be reviewed, based on the progression of the disease.

All horses stabled at Woodbine must have their temperatures taken and recorded visibly on the horse’s stall door for inspection. Trainers with horses that have clinical signs consistent with EHV-1 infection (including fever (101.5 F/38.5 C or above), respiratory signs (cough, nasal discharge and/or neurological signs) must report these findings to their veterinarian immediately.

Horse people who had horses at Woodbine Racetrack within the last 7 days should monitor their horses for any signs of illness. Standardbred horses are not stabled at Woodbine Racetrack. As well, the standardbred racing meet concluded at Woodbine on May 20, 2013 and moved to Mohawk Raceway on May 23. Therefore the June 15 North American Cup at Mohawk will not be impacted by these measures.

As with most outbreaks, the next few days are critical to see how far the virus has spread. Early on, you never know whether it's confined to a specific barn or group, or whether it's widely disseminated across the facility. An outbreak that just affects one barn is still a problem, but it's much easier to contain than one that's already moved beyond the initial group. Without knowing how the first horse was infected (something that's rarely identifiable), time and testing are needed to determine the extent of the spread and how hard it will be to contain it.

Bloodstream infections in horses from contaminated fluids

The latest edition of the University of Guelph Animal Health Laboratory's newsletter contains an interesting report about 4 horses that died over the past few years from what was suspected to be contaminated intravenous fluid solutions. These cases were dead horses that were submitted for post-mortem examination from three different farms, so if anything, this could be an underestimation of the problem.

The first two horses were from the same farm. They were young Thoroughbreds that were routinely treated with intravenous electrolytes, vitamins and minerals (whether by the trainer or veterinarian is unknown). The first horse was found with its head hanging low after treatment. It later developed seizures and died. The second horse showed similar signs. The bacterium Klebsiella pneumoniae was isolated from a few different tissues of the first horse, as well as one of the "jugs" used to administer the fluids. The second horse had the same general lesions as the first, but Klebsiella wasn't isolated; however, this may have been because the body wasn't in great shape by the time it was submitted to the lab, and various other bacteria had overgrown the Klebsiella, making it difficult to isolate.

Another case was a young Standardbred that died after receiving intravenous fluids with vitamins, and a glyceryl guaiacolate jug. It had signs of bloodstream infection (septicemia) and Klebsiella oxytoca was isolated from multiple organs. Various bacteria were isolated from remnants of fluid in treatment bottles.

The final case was a five-year-old Standardbred that died after receiving a home-mixed vitamin jug. It had lesions similar to the other horses and consistent with a bloodstream infection. Klebsiella oxytoca was isolated from multiple organs.

Contamination of multidose drug vials or fluid solutions can occur if bacteria are inoculated into the bottle with a needle when a dose if withdrawn. We've shown this happens with multidose vials in a hospital situation, and of the farm it's even more likely to occur because it's a dirtier environment and, in the case of farm personnel, individuals have less experience with sterile technique. Fluid solutions can be contaminated in the same manner or when something is added to the fluids (e.g. vitamins). Contamination of reused fluid administration sets (i.e. fluid jugs/bags and the IV tubing) is quite likely, and that's why use of sterlie, single-use administration sets is recommended. Adverse events from a little bit of contamination are uncommon, but as shown here, they can happen and they can be severe. There's no information about what contributed to the contamination in these cases, but it's almost certain that poor infection control practices were at the root of the problem. Trying to save money by skimping on sterilization, reusing items without proper care, and using poor hygiene practices in general can end up costing much more.

Protocols for contagious diseases at horse shows

Horse show season is upon us, and with it comes the questions from concerned horse owners who want to protect their animals from the infectious diseases they may encounter at these events.  In this case, the specific question is:

What protocol would go into place if a horse with a highly contagious disease such as EHV-1 were to be found at a competition in Canada?

The short answer (to the surprise of many) is that there is no pre-established nation-wide protocol for most equine disease outbreaks.  Every outbreak is managed differently, based on the disease, the types of horses, where exposure might have occurred and a range of other factors. Typically, a disease like EHV isn't going to be noted during the show, since it takes some time for illness to develop after exposure. Therefore, the response is more of an investigation of what happened at the show, why and how it can be prevented in the future, and of course trying to prevent further transmission in the community (e.g. identifying exposed horses, communicating with people who have been to the show with recommendations to quarantine and test exposed horses and potentially all horses, surveillance for ongoing transmission from horses that have left the show).

With horses, there's no regulatory body with a mandate to oversee (and fund) this type of investigation unless it's a federally reportable disease like rabies (and even then, assistance may not be forthcoming). Some provinces have more authority and interest (e.g. the Animal Health Act in Ontario gives the province a mandate and powers to intervene) but often investigation is not a priority for regulatory bodies and it's left to whoever is around and interested. There are some good outbreak management guidelines from different institutions or groups (e.g. the ACVIM consensus statements on EHV and strangles) but there is no standard approach. Because testing costs are placed on the owners, responses can be quite variable since getting people to test when indicated can be a challenge. Additionally, getting people to follow quarantine recommendations is a challenge because of inability to effectively quarantine on their farm or unwillingness to do so (usually more the latter). So, each outbreak ends up being managed quite differently.

In general, the key points to outbreak investigation and management are:

  • Identification of a problem
  • Diagnosis of the problem
  • Communication to let people know what's happening
  • Identify potentially exposed and infected horses
  • Quarantine, if appropriate (usually some form of quarantine is indicated, but not necessarily for all diseases)
  • Develop testing recommendations
  • Develop and communicate a plan to maximize compliance with quarantine and testing
  • Create a way to centralize data collection and communications, so that a clear picture of what is happening is obtained
  • Keep people in the loop as the investigation ensues to maximize compliance and decrease loss of compliance because of boredom or fatigue with the recommendations

Another Australian bat virus in horses

As if horse owners and veterinarians in Queensland need another infectious disease challenge.....

Recently, a horse in southwest Queensland was diagnosed with Australian bat lyssavirus infection. This virus, which is similar to rabies, is present in some bats in Australia. It can be transmitted to people from bats, causing fatal disease, but human infections are very rare. Even though it's rare, it warrants attention because the disease is so severe.

Finding an infected horse is surprising in some ways, because the virus has never been detected in this species before. However, a virus that's present in bats can certainly find its way into a horse, and we already knew that a closely related virus (rabies) can infect horses. So, maybe it's not that surprising afterall.

In this case, the horse was suspected of being infected with Hendra virus initially. While Australian bat lyssavirus can kill people, this diagnosis was actually much better than Hendra virus infection, because horse-human transmission of Hendra is a major concern. Hendra virus infections have high fatality rates and, perhaps most importantly, there are no effective preventative measures that can be taken after Hendra virus exposure. Since Australian bat lyssavirus is so closely related to rabies virus, rabies post-exposure treatment can be used in this case (and is probably effective).

It's unclear whether an infected horse poses much risk to people. The very small number of human Australian bat lyssavirus cases have occured in people who were bitten or scratched by bats. Since this is the first equine case, it's not known if affected horses shed large amounts of (or any) virus. People who had contact with the horse were identified and offered post-exposure treatment. It's reasonable to consider this situation like rabies exposure in the absence of more evidence, and treat people who were bitten or otherwise may have gotten virus-contaminated saliva into their tissues via broken skin or mucous membranes.

Is this the start of yet another new problem?

Most likely, this is just an example of the rare scenario of a virus infecting an atypical host, not the start of a new, common problem. However, it's worthy of attention in case the virus has changed or there is now a specific virus type that can more easily infect horses (both very unlikely). This case also shows the importance of thorough diagnostic testing, particularly when an animal has severe disease.

If you don't look, you don't find.

If you don't find, you can't act.

Equine herpesvirus in Ontario

I’ve received a lot of emails over the past 24 hours about the recent report of equine herpesvirus type 1 (EHV-1) neurological disease in an Ontario horse. The two main questions are whether there’s an outbreak and whether horse owners in Ontario should be concerned.

I don’t have any firsthand knowledge about this case (or any information beyond what’s been written elsewhere), but as far as I know, this is just a single sporadic case. That doesn’t mean an outbreak can’t occur, but most often, these just occur singly.

Whether there’s cause for concern is a tough question to answer. Yes, EHV-1 can be a serious problem, causing neurological disease in adult horses, abortion in pregnant mares, and severe disease in neonatal foals. Yet, at the same time, it’s an endemic disease that most often occurs as sporadic cases rather than large outbreaks (people just don’t hear about single cases as often, although they are now reported a lot more than they were a few years ago). The EHV-1 virus is very common and can be found in its dormant form in a large percentage of horses, so it’s not like some pathogens with which an unexposed population can suddenly be threatened when a single case is identified. In general I pay close attention to EHV-1 cases, but they are not a cause for panic. If a case occurs, we need to see if some broader issue is at play, and put steps in place to limit the problem, but we don’t need to cause massive disruption. In short, we want to ensure that good surveillance and infection control measures are in place, but not freak out in the process.

People have really taken a 180 degree turn in how they handle EHV-1 over the past 10 years or so. I don’t think we see EHV-1 neurological disease any more than when I was a resident. Back then, we saw sporadic cases and the odd small cluster, and people didn’t get too worked up about it in terms of the risk of transmission. Outbreaks, such as one I can remember associated with a large Ontario Standardbred yearling sale, certainly got lots of attention, but it was short-lived. Things changed (for good reason) based on some large, high-profile outbreaks in the last decade.  It’s not known why such outbreaks now seem to be more common.

Anyway, if you live in Ontario and have a horse, don’t panic. Your horse is probably at no greater risk today than it was last month, assuming it wasn't in contact with the affected horse (which was diagnosed in early April). Virtually every horse is at some degree of EHV risk every day, but the odds of disease occurring are very low.

Some key prevention tips include:

  • Use good general infection control practices to reduce exposure of horses to pathogens brought in by newly arrived horses.
  • Observe your horses regularly and if there are any problems, isolate the horse and have a veterinarian examine it ASAP.
  • When travelling to shows, races or other events, take measures to reduce direct and indirect contact between horses.


Antimicrobial stewardship: Time for change

A call to arms from guest blogger and University of Guelph professor, Dr. John Prescott:

Watching the global emergence and spread of multi-drug resistant bacteria is like seeing a train wreck in slow motion. There’s a sense of both inexorability and powerlessness. In the March 2013 issue of the Equine Veterinary Journal, Mark Bowen of the School of Veterinary Medicine and Science, University of Nottingham, writes that there is clear evidence of the need for change in our relationship with antimicrobials. Change is what many bacteria do for a living; of course the problem is not that bacteria change to resistance, but also that people are so resistant to change.

The excellent editorial (“Antimicrobial stewardship: Time for change”) describes the sensible steps taken by the British Equine Veterinary Association (BEVA) in 2012 to promote the stewardship of antimicrobial drugs in horses. These steps are summarized on the BEVA website: They provide an excellent approach to stewardship of antimicrobials in horses. BEVA has developed neat and simple promotional material to help equine veterinarians using these drugs do their part to help preserve them.

The BEVA project is summarized by the acronym PROTECT ME, which encompasses 9 steps to promote stewardship. PROTECT comes from for Practice policy; Reduce prophylaxis; Other options; Types of drugs and bacteria; Culture and sensitivity; Treat effectively, and ME come from Monitor and Educate. The brilliance and perhaps even contrariness of the BEVA approach is that it believes that policies should be created at the local level, and should be both dynamic and follow simple key concepts, rather than be national guidelines developed by people working in ivory towers.

The BEVA website provides the templates and forms for equine practitioners everywhere to develop simple and local policies that commit to stewardship. An important element in the PROTECT ME documents is to try to protect the drugs classified by the World Health Organization as the “Critically Important Antimicrobials” (3rd and 4th generation cephalosporins, fluoroquinolones). These drugs are categorized as “protected”. Drugs such as vancomycin and imipenem are categorized as “avoided”. The PROTECT ME approach promotes the use of “first line” antimicrobials as first choice for treatment of common conditions as part of the practice policy, and link this to the British “cascade” approach to antimicrobial drug choice. The BEVA approach is refreshing because it takes an intelligent, long-term approach that embraces the responsibility that users share to preserve the miracle while our scientists work feverishly to develop the next generation of antimicrobials. These are however going to be extremely expensive and perhaps also unavailable for animal use, except perhaps through the black market. 

The antimicrobial “miracle drugs” revolutionized medicine and came into widespread use long before there was any science behind their optimal use. We’re still discovering how best to use them but we need to continue to develop strategies and approaches that optimize their use and minimize resistance and other side effects. The easily followed BEVA approach encourages user engagement with and responsibility for stewardship. Change is painful, but we have no choice. Let’s embrace it.  


Equine MRSA in Israel - Different strain, same old tricks

It's been quite a while since the last post about MRSA in horses, but rest assured, it's still out there!  Not too surprisingly it's also spreading (or at least starting to be found) in new places.  A recent report in Veterinary Microbiology (Schwaber et al, 2013) describes an MRSA outbreak at a large animal teaching hospital in Israel.  It is the first report of MRSA colonization in horses in the Middle East, although it's possible (and quite likely) that there's more to be found.

The discovery of the problem had a pretty typical progression: there were two horses in the hospital with post-operative wound infections from which Staphylococcus aureus was cultured, and the isolates from both horses had similar antimicrobial resistance patterns, including resistance to all beta-lactam antimicrobials (= MRSA). Validly concerned about the potential for the MRSA to spread among horses and people in the hospital, an investigation ensued - in this case the National Center for Infection Control (NCIC) was actually called in to coordinate the operation.

  • They found MRSA in 12/84 (14.3%) horses, of which 11 were in the hospital at the time of sampling, and 1 had recently been discharged from the hospital.  Consider though that 44 of the horses sampled were simply from farms from which an MRSA-positive horse had come - so 11/40 horses in the hospital were positive - that's 27.5%!
  • 16/139 (11.5%) of personnel at the teaching hospital were positive for MRSA.  Fortunately there were no clinical MRSA infections reported in people.
  • The MRSA strain that was found in all the horses and most of the people was a very rare type - not the usual sequence type 8 (ST8) we're used to finding in horses in various other parts of the world.  This one was an ST5, spa-type t535, SCCmec type V, which is even rare in the human population.
  • The primary action taken to get the outbreak under control: increased infection control measures, including isolation of infected and colonized horses which were then handled with contact precautions (e.g. gloves, gowns), discharging horses from hospital as soon as medically possible to decrease transmission pressure, and having a nurse from the NCIC come in to instruct personnel on the measures to be taken, including emphasis on hand hygiene and increased use of alcohol-based hand sanitizer.
  • In this outbreak, decolonization therapy was prescribed for all colonized personnel.

The report does not mention whether or not personnel at the hospital were required to submit to being tested and undergoing decolonization therapy.  This can be a very tricky issue to handle, and it depends on what the local laws are.  In Canada, employees cannot be forced to undergo testing or treatment, but in some other countries MRSA-positive healthcare workers may not be allowed to even work until their carrier status is cleared.

Interestingly enough, just a year or two before this outbreak occurred a study (as yet unpublished) had been carried out in the same region, during which they found MRSA in 7.2% (6/83) of hospitalized horses and none in horses from local farms.  There is no mention regarding whether or not the hospital had taken measures to eradicate MRSA from the facility before the clinical infections that triggered the outbreak investigation occurred.

This was a typical MRSA "iceberg" - a couple of clinical cases were triggers for an investigation that found a lot more horses and people were actually carriers.  This is exactly why it's important to remain diligent about infection control measures like hand hygiene at all times, so that pathogens like MRSA don't move in "under the radar."  The authors of the paper summed it up nicely (although I'd leave out the part about decolonization):

"Strict implementation of hand hygiene, isolation of colonized and infected horses, decolonization
of colonized personnel and above all, constant education of veterinary students and personnel about the importance of infection control measures are required in order to decrease the risk for colonization and infection of both horses and personnel by MRSA and other pathogens."

More information about MRSA in horses is available on the Worms & Germs Resource - Horses page.

Equine herpesvirus in Michigan

Yes, the title's a bit misleading. Equine herpesvirus (EHV) is everywhere, since the virus circulates widely in the horse population internationally and lies dormant in the bodies of a large percentage of healthy horses. However, cases of EHV-1 neurological disease get attention because of the severity of disease and the potential for outbreaks (for reasons we really don't fully understand). Seeing a report of a new case isn't surprising, since they are always occurring somewhere, but it's worthy of note for horse owners in the area or those who might have visited the area recently.

The latest incident, reported by, involves a Standardbred horse that raced at Sports Creek Raceway, a small track in Michigan. The animal raced on December 22nd and started showing signs of neurological disease on December 23rd. It presumably didn't pick up the virus at the track, because 24 hours is on the very low end of the potential incubation period, so the main concern is that the horse might have been shedding the virus while at the track. It's possible that EHV could have been transmitted to other horses via aerosols (virus on small particles released when the horse was breathing, shorting or coughing), contaminated items that were used for multiple horses (e.g. buckets), or on the hands or clothes of people. That's why good general infection control practices are needed at tracks and other horse competitions at all times - to reduce the risk of transmission when an infectious but currently healthy animal is present (and there's room for a lot of improvement).

Typically, the incubation period of EHV-1 in a neurological disease outbreak isn't very long: about 4-6 days or so. If anyone had a horse at the track on the 22nd and it's still healthy today (January 4th), odds are it won't be affected. However, there are some instances when the incubation period can be longer, particularly with abortions in pregnant mares. Also, horses could have been infected and not gotten sick, but still be able to spread the virus to other horses with which they subsequently have contact. For this reason, several racetracks have imposed temporary entry restrictions on horses that were at Sports Creek in December. It's probably a low risk situation, but you can never put an outbreak "back in the bottle," and a little short term inconvenience is much better than the major hassles (and deaths) that can come with an outbreak.

The affected horse was in pretty rough shape neurologically but ultimately recovered, as can occur with EHV-1 neurological disease. If your horse has to have a neurological disease, this is probably one you want since full recovery is possible. EHV-1 will probably live within this horse's body for a while, if not lifelong, but that's true of a large percentage of other horses as well, so after a few weeks (when the likelihood of him shedding the virus decreases), he probably poses no more risk than any other horse.

MRSA in an alpaca

Following up on my recent post about MRSP in rats, here’s a story about MRSA in an alpaca (Stull et al, Can Vet J 2012). As far as we know, it’s the first report of MRSA in an alpaca (or any camelid).

The report relates to our large animal hospital, where we perform MRSA screening of all horses at admission, weekly during hospitalization and at the time of discharge. It's all part of our infection control program, and the screening is designed to help reduce the risk to horses and our hospital personnel, since this multidrug-resistant bacterium is endemic in the Ontario (and broader) horse population, and outbreaks can occur in equine hospitals.

While alpaca’s aren’t horses, and we don’t see that many of them here, they sometimes get screened anyway since screening is being done on most of the other patients.

This case involved a neonatal alpaca that was admitted with its mother because of severe respiratory disease. The cria (baby alpaca) was very sick and was ultimately euthanized about 36 hours after admission.

Surprisingly, the admission MRSA sample from the cria was positive. In this case, MRSA wasn’t involved in the animal's illness. The cria didn’t have any evidence of bacterial infection, so this was an incidental (but interesting) finding.

When the bacterium was tested further, it was classified as CMRSA-5 (Canadian epidemic MRSA-5), a human strain that also predominates in horses in North America. The mother alpaca was MRSA negative. Presumably, the cria picked up MRSA from the farm environment or a person shortly after birth. MRSA (especially CMRSA-5) carriage rates are high amongst horse owners and horse vets compared to the general public, and it would have been nice to have determined if there were any horses on the alpaca’s home farm, but we couldn’t get any follow-up information.

This single case is probably of limited concern in the grand scheme of things. It’s likely an "oddball" infection rather than an indication that MRSA is a serious threat to alpacas, or that alpacas are a relevant source of human MRSA infection. However, that’s largely what was said when MRSA was first found in horses in the late 1990's and early 2000's, and it has since become a significant issue in that species, so the potential for MRSA to become a problem in alpacas can’t be completely dismissed.

If nothing else, the occurrence of this case is an indication of the need think broadly when it comes to infectious diseases, since many pathogens don’t have species boundaries. CMRSA-5 is a human-origin MRSA strain, but it’s worked its way outside of its natural host. It’s not the first and certainly won't be the last bug to make its way from people to animals.


More equine herpesvirus, this time in Minnesota

I haven’t written much about equine herpesvirus type 1 (EHV-1) outbreaks lately because I have a hard time getting excited about them (from a blog writing standpoint… if one occurs here, that will be a different story). Outbreaks of neurological disease caused by this very common equine virus (one that doesn’t spread to people or non-equids) continue to occur, and it’s hard to say whether we've been seeing more of them over the past couple of years or whether we’re just hearing about them more often. It does seem like outbreaks have truly become more common and more virulent in the past 10 years or so, but I’m not sure it’s continuing to get worse.

The latest EHV-1 outbreak has affected 5 of 7 horses on a central Minnesota farm. At last report, one horse had been euthanized and one was hospitalized at the University of Minnesota. The hospitalized horse is presumably receiving supportive care, such as intravenous fluids and general nursing support. Affected horses may become very weak and sometimes they need to be managed in a sling (see photo), since horses don’t tolerate being unable to stand for long (laying down for prolonged periods of time can damage muscles and nerves, simply because they are crushed by the horse's own weight). Sometimes the bladder becomes paralysed and needs to be drained using a catheter. Numerous other problems can occur since the way this disease affects each horse can be quite variable. Fortunately, the prognosis tends to be reasonable (at least compared to other neurological disorders) if the horse is not severely infected and stays standing or is able to remain upright with the support of a sling. The clinical signs are the result of inflammation of the blood vessels in the brain and spinal cord, and the key is to get that inflammation down and keep the horse alive in the meantime.

In the past, we didn’t worry too much about these horses in equine hospitals. EHV-1 neurological disease tended to occur sporadically, not in the form of outbreaks, and dogma was that once the horse was sick, it wasn’t at much risk of shedding the virus. In fact, for a long time our best stall in the main hospital for neurological cases (which had padded walls, and a ceiling anchor for a sling) was right at the front of our main equine ward. A large outbreak in the US in the early 2000s changed that, and now we take much more aggressive measures to contain this virus, including housing affected horses in isolation and using strict infection control measures. With these precautions, the risk of spreading the virus in an equine hospital is low.

Image: A horse with neurological disease being managed in a sling (source:

Hendra vaccination now a reality

In a rather impressive effort - considering the issues inherent with working with a virus like Hendra virus, the nature of the disease and the low economic value of a vaccine that would only be used in a very restricted geographic area - a Hendra virus vaccine has been released for horses. Equivac HeV should provide a degree of relief to people in Queensland and neighbouring areas who have been battling this uncommon but devastating bat-borne viral infection.

As a virus that comes from wildlife, Hendra virus is tough to contain. Eradicating the virus in the bat population isn't really feasible, and while measures can be taken to reduce exposure, the risk cannot be eliminated in areas where the virus is present. So, finding a way to reduce the risk of a horse developing the disease after exposure is critical, and the logical approach is vaccination.

Vaccination of horses can also play a huge role in protecting people. All human Hendra virus infections (approximately 50% of which are fatal) have come from direct contact with infected horses, so reducing disease in horses should reduce the risk in humans.

As with most vaccines, it's safe to assume this one isn't 100% effective. It therefore may be a great tool, but people can't then ignore all other Hendra avoidance practices.  Individuals still need to take precautions when working around horses that might be infected, regardless of their vaccination status. So, while it's important to avoid complacency, this vaccine should provide a degree of comfort to people who have been living with this virus hanging over their heads (both figuratively and literally, as bats fly around) in recent years.

(click image for source)

Streptococcus zooepidemicus: Bar-coding the bad guys

Here is another equine update from guest blogger, Dr. John Prescott of the University of Guelph.

Research presented at the Ninth International Equine Infectious Disease conference last week in Lexington, Kentucky, highlighted the dramatic impact that the latest inexpensive genome sequencing techniques are having on understanding microbial disease. 

This is well illustrated by an epidemic of S. zooepidemicus upper respiratory tract infection in horses that occurred in Iceland in 2010, described by lead author Sigrídur Björnsdóttir of the Icelandic Food and Veterinary Authority. The infection itself was relatively mild but lasted about 4 weeks, and over the course of the summer affected a large proportion of Iceland’s horses. It caused a headline-stopping movement and export of horses. The disease presented as a laryngitis and persistent dry cough, with a serous [watery] nasal discharge. The infection started at a facility with a water treadmill, and was rapidly disseminated by horses moving from there to 18 other centres across the country, with a high transmission rate to horses within these stables. Since S. zooepidemicus was isolated from the nasal exudate only as the disease progressed, veterinarians investigating the outbreak thought at first that these isolates were opportunistic or secondary invaders, layered on top of an unknown virus infection.

This is where bacteriologists Andrew Waller and Carl Robinson from the United Kingdom’s Animal Health Trust in Newmarket and Matthew Holden from the Sanger Centre in Cambridge became involved. Incredibly, these researchers sequenced the genomes of 290 isolates from the outbreak as well as from an earlier national collection. They used this information to find, to their astonishment, that S. zooepidemicus Sequence Type 209 was responsible for the outbreak. This strain was isolated from the affected farms all over the country, as well as from a case of miscarriage in a person. It could clearly be linked epidemiologically to the outbreak; the date that the infection started was pinpointed to within 5 days. The epidemic occurred so quickly that the genomes of this strain showed almost trivial variation compared to S. zooepidemicus strains that were more established in Icelandic horses.

This is the best description ever of the impact of introduction of a more virulent S. zooepidemicus into a naïve horse population, and will change forever the way that equine veterinarians will think about this underrated pathogen. It illustrates the enormous power of genome sequencing in bar-coding the bad guy.

Andrew Waller also gave a really interesting talk about the diversity of S. zooepidemicus. Sequencing and “sequence typing”, based on multilocus sequence typing (MLST), has identified over 300 sequence types of this species. What is emerging from this is the recognition that difference types cluster with different diseases. For example, strains (sequence types) of S. zooepidemicus that cause abscessation of pharyngeal lymph nodes (“mild strangles”) belong to sequence types that have acquired a bacterial virus carrying a superantigen gene. These are, of course, outclassed by the true strangles organism, S. zooepidemicus subspecies equi, which possesses four bacteriophages with these virulence genes, as well as other nasty characteristics.

Andrew Waller told me that it cost him about $35 to sequence an entire streptococcal genome, which for Canadian veterinarians is now about the cost [Weese comment: or much less than the cost] of sending a swab to a diagnostic lab for culture and sensitivity testing. However, don’t start ringing up the lab to ask for a genome sequence just yet, since the real cost is for the analysis, which is still labour intensive. However, it points the way to the future, which has clearly now arrived, and is changing the way we think about S. zooepidemicus and infection in the horse.


Identifying the "right" parasite control program

Here is another guest blog, this time from the "worm-guy" Dr. Martin Nielsen of the Gluck Equine Research Center at the University of Kentucky.

At the recent 9th International Conference on Equine Infectious Diseases (EIDC) in Lexington, Kentucky several sessions were focused on parasite control of horses. Drug resistant parasites are a world-wide problem in equine establishments, and it has become a challenge to define a simple and useful set of guidelines to be used by horse owners. As many readers of the Worms & Germs Blog will be aware, there is no longer a “one size fits all” program, and parasitologists instead often talk about the complexity related to the different parasites that often infect the horses in concert, their interactions with their hosts, and how to interpret fecal egg counts. While this is all useful and important information, it can be frustrating when it does not readily come with some practical guidance.

Equine parasitology is rarely well-represented at parasitology conferences. Usually, there are less than a handful equine abstracts, and often not even enough for a separate session. The three or so participating equine parasitologists often have to create their own little scientific session over a cup of coffee during the breaks. The EIDC was much different. It had participation from leading equine parasitologists from Sweden, Denmark, Finland, Germany, United Kingdom, Canada, Brazil, and the USA. More than 30 parasitology abstracts were presented at the meeting, and a special session critically addressed the most pressing research needs for equine parasite control. During the conference, an international equine parasitology consortium was formed, and it will serve to coordinate future research efforts and to communicate consensus-based guidelines for parasite control.

So, what are these recommendations then?  New research presented at the EIDC illustrated very well that general recommendations are more straight-forward than often anticipated. Work performed by Kurt Pfister and colleagues in Germany illustrated that fecal egg counts are useful for monitoring and controlling parasite transmission by the means of selective therapy. Two Danish studies illustrated that one or two yearly strategic treatments applied to all horses are advisable to effectively break the life cycle of large strongyles, particularly the bloodworm, Strongylus vulgaris. In other words, a basic foundation of treatments can be defined, upon which the some of the more parasitized horses can be identified to receive additional treatments with a selective approach. Several presentations underlined the need for yearly routine evaluations of the efficacy of the anthelmintic drugs used on each farm. The fecal egg count reduction test is the most important use of the fecal egg counts. [Weese comment: that's when you do a fecal egg count before and after deworming, and compare the egg counts to see how much they dropped, as an indication of how well the dewormer worked] Perhaps most encouraging was the promising new diagnostic tools presented by several groups for detection of migrating or encysted parasite larvae. These will turn very useful for identifying horses at risk of disease and in need of deworming. One of these, developed by Jacqui Matthews and her group at Moredun Research Institute in Scotland shows great promise for measuring burdens of small strongyle larvae (cyathostomins), which can pose a threat for severe parasitic disease. With these new tools in hand, we will become able to further refine our recommendations in the future.

Will genomics eradicate strangles?

More from the International Conference on Equine Infectious Diseases, this time from guest blogger and bacteriologist-extraordinaire, Dr. John Prescott of the University of Guelph:

Stellar work on understanding strangles and Streptococcus equi subspecies equi was presented at the Ninth International Equine Infectious Disease conference in Lexington, Kentucky. Researchers at the Animal Health Trust in Newmarket, United Kingdom (Andrew and Carl Robinson) are working with Matthew Holden at the Sanger Centre in Cambridge to use NextGen sequencing to understand better the strangles bacterium, and the impact of the carrier state on the pathogen as it lurks in the guttural pouch. The abstracts of their work are freely available through the conference web site,

A novel quantitative PCR (qPCR) based on two unique genes of S. equi was was described that will identify S. equi within 2 hours, with a sensitivity of 93% and specificity of over 96%. Not only is it more sensitive than culture but it also overcomes the effects of non-S. equi contaminants which can interfere with culture. Another development reported was an ELISA based on two antigens unique to S. equi that together have a similar sensitivity and specificity to the qPCR. Current thoughts are that the ELISA could be used as a serological test in screening for carriers, with the qPCR then being used on guttural pouch aspirates to confirm the carrier state, which would then be treated.

The strangles (equi) subspecies of S. equi has been thought to be genetically and immunologically identical, but sequencing the M protein SeM gene has shown that there are over 100 strains. Holden and his colleagues have used high throughput sequencing to characterize the genomes of an astonishing 240 isolates from different countries, including one strain from Canada. They have found that genomic diversity is even higher than SeM sequencing had suggested. As a result of this work, they identified a “fitter” clone (ST151) now spreading through the UK population at the expense of an older clone (ST179).

Most interestingly, they have identified the genetic changes occurring as outbreak strains adapt to their different life in the guttural pouch, which is where the organism hangs out in carrier horses. The adaptation involves discarding some genes, stopping the expression of others, but also duplicating others. According to Holden, a Sanger Centre genome veteran, the S. equi genome is more dynamic than any of the other pathogens with which he has worked. The big question is of course the impact of this adaptation on virulence, and the extent and speed with which these genetic adaptations can be reversed if and when the “carrier“ strains revert to cause acute strangles. There is a horrible suspicion that some may be able to borrow back the deleted genes from other S. equi strains in the guttural pouch.

Because of both its species- and niche-adaptation, strangles has all the characteristics of a bacterial infection that can be eradicated. The superb work being done at the Animal Health Trust, all based on genomics, is drawing the noose ever tighter around this ancient scourge of the horse.

- John Prescott, Department of Pathobiology, University of Guelph


Equine coronarvirus...a new problem?

Two presentations at the International Conference on Equine Infectious Diseases yesterday discussed equine coronavirus and whether it might be a new or previously unrecognized cause of disease in adult horses. This follows a presentation the day before that mentioned coronavirus diarrhea in racing draft horses in Japan - a rather unique group, pictured at right.

Dr. Nicola Pusterla from the University of California Davis described five suspect outbreaks in boarding facilities from four US states. Seventy-three (73) horses were affected overall, with decreased appetite being the most common sign in affected horses, followed by lethargy, fever, soft manure and colic. Equine coronavirus was detected in the vast majority of sick horses but rarely from healthy horses at the same facilities. Most horses got better without specific treatment, but five horses died or were euthanized. Overall, the attack rate on farms was high but the death rate was low. Fortunately from an infection control standpoint, infected horses only shed the virus for a short period of time (a few days), making control easier.

Dr. Ron Vin followed this presentation with a description of coronavirus involvement in sporadic disease and outbreaks in adult horses from a variety of US states, most often with mild diarrhea and low white blood cell counts. As with the first report, disease severity was usually less than what we see with some other causes of diarrhea in adult horses, such as Salmonella and Clostridium difficile.

One thing that’s not clear is whether this virus is truly a cause of disease or something that’s just being found in horses that have some other undiagnosed disease. No other potential causes were identified in most of the suspected coronavirus infections, but a large percentage of cases of diarrhea that we see go undiagnosed because we don’t know all the possible causes. It’s certainly possible that there was another cause, but these results suggest that equine coronavirus is something for which we should be looking out when we see gastrointestinal (e.g. colic, diarrhea) or non-specific disease (e.g. off feed, lethargic with no other particular signs), especially during outbreaks. The story may be different in foals, since shedding of the virus by healthy foals isn’t uncommon.

Photo credit:

Canine flu: Risk to horses?

I’m at the International Conference on Equine Infectious Diseases in Lexington, Kentucky at the moment, and will try to write about some of the highlights. One interesting discussion yesterday was about canine and equine influenza. It’s well established that canine flu (A/H3N8) originated in horses and subsequently became established in dogs. Canine flu virus is closely related to, but different from, its equine flu virus parent. That raises questions about whether canine flu virus could be transmitted back to horses. The question has significant implications for what should be done with dogs that might have canine flu that may have contact with horses, and for canine-horse contact in general, especially with performance horses.

A study by Yamanaka et al. (Acta Vet Scand 2012) looked at dog-horse infectivity of canine flu by putting infected dogs in stalls with healthy horses for 15 days. All dogs were sick and shedding canine influenza virus, but none of the horses got sick, shed the virus or mounted an antibody response. This study only involved three horse-dog pairs, so we have to be careful that we don’t go too far with the conclusions, but it suggests that while canine flu started off as horse flu, it has changed enough that infected dogs aren’t much of a risk to horses.

But... (yes, there’s usually a "but" with infectious diseases) dogs are susceptible to "normal" equine influenza. It’s uncommon, but dogs can be directly infected from horses with the classical equine H3H8 flu virus. In such a situation, dogs might pose a risk to horses because they are carrying the  equine virus, not the adapted canine version.


  • If a dog has influenza that is known to be non-horse associated (i.e. typical canine flu) then there’s probably little concern for horses.
  • If a dog has influenza and there’s no clear dog link (or there’s a link with infected horses), it’s reasonable to assume that the dog could transmit the virus to horses.

However, why take the chance? It seems logical to ban any dog with a suspected respiratory infection from horse barns. It also makes sense to ban dogs from barns with equine flu cases. It’s an easy, cheap, minimally disruptive and potentially useful flu control measure that might help reduce transmission of this important virus in both directions.

Ontario restrictions on Illinois race horses

In response to an equine herpesvirus type I (EHV-1) outbreak at Hawthorne Racecourse in Illinois, the Ontario Racing Commission (ORC) announced movement restrictions on horses from Hawthorne, and Illinois in general.

Effective immediately:

  • Any horse that has been on the grounds at Hawthorne since Oct 4 is not allowed on any Ontario racetrack until 30 days after Hawthorne's quarantine is lifted
  • All horses from Illinois being shipped into the Woodbine or Fort Erie racetracks must come with a certificate that states "Horses represented on this Certificate of Veterinary Inspection have not originated from a barn or premises that is under quarantine for herpes virus, nor have been exposed to a confirmed or suspect case of herpes virus, nor have shown clinical signs suggestive of herpes virus, nor have been febrile within the previous three weeks."

All other tracks are also advised to be cautious about accepting horses from Illinois, but restrictions are at the discretion of individual facilities.  The ORC is also recommending that all horses from Illinois are examined and their temperatures are taken prior to being admitted to any track.

Basic physical examination and body temperature checking can be great infection control measures when used on a routine basis. Too many sick horses make it onto tracks, show grounds and into sales, and while checking temperature is by no means 100% protective, it's an easy, cheap and a quick way to identify potentially infectious horses. Yet, it doesn't happen. Considering the potential implications of a single infectious horse making it onto a track, it doesn't make sense that more effort isn't put into routine practices like these. Yes, it would take a couple minutes, but if it prevents one infection (let alone an entire outbreak), it's worth the minimal effort.

As an aside, I've always been baffled why places like yearling sales won't consider employing such measures -  well, maybe not baffled because sending sick horses home costs the sale money.  But considering how common infectious diseases are in horses after sales, it's hard to understand why buyers are not pushing sales to do what they can to make sure buyers aren't spending big money on damaged goods, i.e. sick horses. I'd like to think that a sale could make it a great marketing point by touting their strong infection control program to convince buyers to come and spend their money with less chance of getting a sick horse.

It's always hard to say what the best approach is for handling EHV infections. On one hand, it's a very common virus that is lying dormant in the bodies of a large percentage of healthy horses, everywhere. On the other hand, we certainly know outbreaks of serious disease happen and horse-horse contact and movement of horses helps outbreaks spread. These Ontario restrictions are pretty straightforward and common sense, but thought should be given to what other measures can be taken on a routine basis to help reduce the risk of EHV-1 outbreaks from developing in Ontario, and to control the numerous other infectious diseases that affect more horses every year.

2011 US Rabies recap

The annual US rabies surveillance report has been published in the latest edition of the Journal of the American Veterinary Medical Association (Blanton et al 2012). There's not really anything earth-shattering in it, but it's a good overview of the rabies diagnoses in the US from 2011. As always, it only provides a peek into rabies in wildlife (since only a small percentage of wildlife with rabies get diagnosed and reported) but numbers and trends in domestic animals, along with general wildlife data, provide useful information about the state of this virus in the US. Among the highlights:

  • Rabies was diagnosed is 6031 animals and 6 people, from 49 states and Puerto Rico (Hawaii remains rabies-free). This is a 2% drop in animal cases from 2010, but I don't put much stock in that because the numbers are weighted towards wlidlife cases, and it's hard to have confidence in year-to-year numbers of rabid wild animals (because it's so dependent on what actually gets tested).
  • The main wildlife species that are involved in maintaining the rabies virus in the US (reservoir species) continue to be raccoons, bats, skunks and foxes on the mainland, and mongooses in Puerto Rico. The relative importance of these species varies between regions.
  • Raccoons were the most commonly affected species, accounting for 33% of all rabid animals reported. Other leading species were skunks (27%), bats (23%) and foxes (7%). Less common species included coyotes, bobcats, javelinas, deer, otters, mongooses, wolf hybrids, groundhogs and beavers.
  • Cats were the leading domestic animal, with 303 diagnosed cases. Dogs came in next with 70, followed by cattle (65), horses (44), and goats and sheep (12). There were also single cases in a domestic bison and an alpaca.
  • The six human cases represent the highest annual number of cases since 1994, if you exclude 2004 where four cases were associated with transplantation of organs from a single infected person. In a review of the 24 domestically-acquired human cases from 2002-2011, 88% were linked to bats.
  • Three of the six 2011 human cases were acquired outside of the US; one each from Haiti, Afghanistan and Brazil - and all from dogs.
  • Two of the three domestically-acquired cases were associated with bat contact. The source of the remaining case, an eight-year-old girl, is unknown, but contact with cats from a feral colony near the girl's school is a possibility.
  • 5/6 people with rabies died. That's actually an impressive survival rate, since any survival is still a very noteworthy event when it comes to rabies. The survivor was the eight-year-old girl, and she apparently has suffered no longterm cognitive impairment.

 Interestingly, we get a good synopsis of Canadian rabies data in this report too:

  • 115 rabid animals were identified, with 92% being wild animals.
  • There were three rabid livestock (two of which were horses) and six dogs and cats.
  • No rabid raccoons were identified, continuing a trend started in 2009.

And regarding rabies in Mexico:

  • 148 rabid animals were identified, mainly cattle (82%).
  • Rabies was diagnosed in 20 dogs, with evidence that the canine rabies virus variant (which has been eliminated from Canada and the US) is circulating in some regions.
  • There were three humans cases: two acquired from vampire bats and one from a skunk.

Equine West Nile virus advisory: Ontario

The Ontario Ministry of Agriculture Food and Rural Affairs has issued a disease advisory to Ontario equine veterinarians about West Nile virus (WNV), but not in response to cases of WNV in Ontario horses. In fact, to date, there have been no reported cases in horses in the province this year. However, no reported cases only means no horses have become sick and WNV infection has been considered and WNV testing has been performed. It doesn't mean that no horses in the province have been infected, and as much as anything else, the advisory is a reminder to be aware of WNV and ensure that potential cases are properly tested.

While not anywhere near as bad as the situation in some US states, Ontario has had a larger than expected number of human WNV infections this year, and it's reasonable to assume that many equine infections have (and will) also occurred. Since the end of August is typically the start of the WNV season in horses in Ontario, the next few weeks will tell us a lot about the state of this disease in horses in the province this year.

Banner year for West Nile virus

After being a relatively rare problem in most regions over the past few years, West Nile virus (WNV) case numbers have boomed lately, with large outbreaks in some US states.


Forty-nine (49) confirmed or probable human cases have been reported in Ontario, the largest number in a decade. Considering we're just heading into the typical peak WNV season, it's quite concerning as the worst may be yet to come.  At this time last year, there were only 24 reported cases.

Human cases have been reported in at least four other provinces: Alberta, Manitoba, Saskatchewan and Quebec.

Two equine cases of WNV have been reported, one in Saskatchewan and one in Quebec. It's hard to have a lot of confidence in this number because of the poor surveillance and reporting for this disease in animals in Canada, given that the CFIA has largely washed their hands of dealing with it. Infection with West Nile virus has been pretty much a non-entity in most regions over the past few years, at least in terms of diagnosed cases, and it remains to be seen whether equine cases will mirror the spike in human cases this year. Typically the trends are similar each year, so the next few weeks will tell us a lot.

United States

The US is in the midst of its largest WNV outbreak ever. At least 1118 human cases have been reported so far in at least 37 states, with at least 41 deaths. Typically less than 300 cases are reported by this time of year.  Texas has experienced a huge outbreak, accounting for about half of the US cases.

There hasn't (apparently) been a surge in equine cases, with less than 100 cases of WNV reported in horses as of August 18. Whether that's because of infrequent testing, biological or geographic factors resulting in less equine exposure or vaccination of horses (remember that there is no WNV vaccine for people) isn't clear.

Concern is being raised about risks to pets, but the true risk is very limited. While WNV infections have been reported in dogs and cats, these are extremely rare and dogs and cats are failry resistant to the virus.


Often, when a new infectious disease emerges, the first year or two are the boom years, after which things settle down. That was the pattern with WNV in most areas; however, this year in on track to meet or surpass the numbers from those early years.

Why is this happening? No one knows for sure. Changing weather patterns, by chance or through the larger spectre of global warming, are probably playing a major role. Warmer temperatures let mosquitoes mature faster and allow the virus to grow quicker in the mosquitoes. Milder winters help mosquitoes survive. Any factor that fosters more mosquito numbers and growth, particularly the subset of mosquitoes that bites both birds (the reservoir of the virus) and people, can increase the risk of human and animal exposure. Changes in rainfall, wetland management, climate and human proximity to mosquito breeding sites can all play a role.

Transfusion-associated equine infectious anemia

A few years ago, I looked out my kitchen window one holiday morning and saw a newborn foal running outside of a fence line. The foal had been born to my neighbours' mare, a maiden mare, and they were out of town. The mare had rejected the foal and wasn't interested in any of my attempts to get them back together. She also had little colostrum (the first, antibody-rich milk that foals need to drink early in life to survive). To make a long story short, I ended up doing a field transfusion, collecting blood from another horse on the farm to give to the foal, to provide it with those much-needed antibodies. The donor horse was healthy and I didn't know of any disease issues in the area, so I was pretty confident that there wasn't a significant risk of disease transmission, but you never know. Ideally, equine blood donors are screened for infectious diseases, particularly equine infectious anemia (EIA), since EIA is a rare but nasty disease that can be spread by blood.

When I started to read a report the other day about a transfusion-associated EIA infection in a German foal, my first thoughts were "that's bad," followed by my ever-optimistic side thinking "well, maybe it was an emergency transfusion and it was a bad but unavoidable consequence" or "maybe it the donor was properly screened but was infected with the EIA virus after it's last test" (the latter situation is an ever-present risk when you are screening donors in advance (days, weeks or months) of collecting the blood for transfusion, since test results only tell you what their status was at the time of testing).

Unfortunately, it didn't take long to see that this wasn't an unfortunate or relatively unavoidable infection. Rather, I can only interpret this as stunning negligence.

Here's the story

  • On August 2, EIA was confirmed in a 3-month-old foal in North Rhine Westphalia. When the foal was two days old, it had a septic joint (and probably an overall deficiency in antibodies) and was treated with a plasma transfusion, which is a pretty standard procedure in such a case.
  • EIA antibodies were then detected in the donor.
  • Since 2009, 20 other horses had received plasma from this horse. Four have been confirmed as infected, and horses that live with these infected animals have been quarantined until test results are back. Positive horses are typically euthanized because they pose a lifelong risk of transmission of the virus to other horses.  The four positive horses in this case have been euthanized (and presumably the foal as well).

So, this wasn't some random emergency field transfusion, or a donor that got infected after testing. It appears that this donor has been used for years with no testing, despite the fact that it's well known that EIA transmission is a risk from blood transfusions and the virus is present (albeit rare) in Germany. While there are no standards of care for equine blood transfusions (as opposed to dogs), EIA testing is a standard recommendation in anything I've seen written about equine blood donor programs (click here for one example). Sometimes you get put into situations where testing can't be done in time for logistical reasons, but I can't see how anyone would not test horses that are to be used for a formal donation program or repeated transfusions. Failure to do low cost and easy EIA screening of that donor horse has resulted in the deaths of multiple horses, with the potential for even broader secondary transmission of this virus to additional animals.

Equine Infectious Anemia: Outbreak Out West

This week an article on discussed the current situation in the western provinces of Canada with regard to equine infectious anemia (EIA).  The prairies are seeing the highest number of EIA cases in years, with more than 70 horses affected on 22 different properties.

Also commonly called "swamp fever," EIA is caused by a retrovirus, similar to the human HIV.  There is currently no vaccine against virus, and once infected a horse carries the virus for the rest of its life.  Although EIA can cause severe clinical signs (including high fever, weakness, swelling of the lower limbs and along the ventral abdomen, and even sudden death) most horses that are diagnosed are not showing any signs of illness at the time, or may show milder, non-specific signs such as exercise intolerance and intermittent fever.  Affected horse of course also have varying degrees of anemia as the name suggests.  Episodes of more severe signs can occur even years after the initial infection, and during these episodes an infected animal poses the greatest threat to other horses because the viral load in the bloodstream is very high.  The virus cannot be transmitted directly between horses though - it is transmitted by blood, typically via blood-sucking insects like like deer flies, horse flies and stable flies (hence the association of the disease with swamps) or by reuse of needles for injections.  Fortunately EIA does not affect humans or any other animal species.  It has also not been shown to be transmitted by mosquitoes.

Because infection is life-long, in order to control the disease the only options for positive horses are euthanasia or life-long quarantine in a building with rigorous insect control to prevent spread.

The question is, why the sudden spike in the number of cases out west?  There are a few possibilities:

  • Possibility #1: There's been one, or a few, small local outbreaks that were initially caused by a very small number of positive horses that likely brought the virus back with them from somewhere to which they had traveled.  Hopefully this is the case, and testing has identified all the horses that were subsequently infected so that the virus won't spread further.  EIA testing is required prior to travel to many places and prior to participating in many competitions or shows.  Regular testing of animals that travel frequently helps to identify infected animals more quickly.
  • Possibility #2: For whatever reason, there are a bunch of horses being tested this year that have not been tested in the past, and they're coming up positive.  This would be much more concerning, because there's no way to tell how long a horse has been infected if it has not been tested in the past.  The longer an infected horse is around outside of a fly-proof quarantine, the greater the chance that an insect (or a needle) will transmit the virus to another horse.
  • Possibility #3: There are number of infected horses across the prairies that have not been tested, and the virus has been slowly spreading from these index cases and has finally reached part of the horse population that does get tested regularly.  This would be the worst case, as it would mean that there's a reservoir of infected horses that is still not being identified, and could continue to perpetuate the infection.

In the end, only time will tell which of these scenarios (or a combination of them) is playing out in western Canada.  Although a relatively low population density (of horses as well as people) in provinces like Saskatchewan helps to decrease the transmission pressure (simply by making it harder for an insect carrying the virus in its mouth parts from one horse to find another horse to bite), gatherings of horses for shows, trail rides and the like (particularly when EIA testing is not required) still create prime opportunities for transmission of the virus.

There are also a few things you can do to help decrease the chances of your horse contracting EIA:

  • Protect your horse from biting insects that transmit EIA (which will simultaneously help protect your horse from insects like mosquitoes that can transmit other viruses).  Use fly repellants, fly sheets, and avoid turnout during times of peak insect activity (dusk and dawn).
  • Never reuse needles, especially between different horses.  Also ensure that any other equipment that may be used on your horse (e.g. mouth gags) are always properly cleaned between animals and free from any blood contamination.
  • Avoid proximity to horses of unknown EIA status.  This can be tough to do if your horse goes to shows where EIA testing is not mandatory, but particularly with the current problems out west (or anywhere else that EIA may be circulating) testing for EIA prior to any event where there will be a gathering of horses should be strongly promoted.

Testing for EIA can be done with a simple blood test.  This used to be called a Coggins test, but now a more accurate ELISA-type test is used to test for the disease instead.

Image: Cross-section of the EIA retrovirus (source: USDA Animal and Plant Health Inspection Service)

Eastern Equine encephalitis alert: Ontario

If I was reincarnated as a mosquito, I'd want to live where I do now (convenient, eh?). I live in the country surrounded by areas of "protected wetland," which, in many cases, is a fancy word for swamp. I try to avoid mosquitoes, but getting bitten is a regular (daily) event. As I was getting swarmed last night, I was thinking that the mosquito-borne disease I'm really concerned about is Eastern equine encephalitis (EEE). While quite rare in Ontario, with only a handful or no cases in horses every year, it's a worry because it's almost always fatal. It also affects people, not via transmission from horses but from being bitten by mosquitoes that pick up the virus from birds. It's very rare in people, but it's highly fatal.

This is the time of year that we start seeing mosquito-borne infections in Ontario, and a Disease Alert from the province re-inforces concerns about EEE. The alert was issued in response to a case of EEE in a horse in New York state, not far from the Canadian border. The horse, from the Ogdensburg, NY area, showed signs of illness on July 23 and died the next day (a pretty typical progression for this disease). Since mosquitoes don't respect borders, cases in this neighbouring region suggest that infected mosquitoes might also be active in Ontario.

EEE isn't the only mosquito-borne virus that we worry about - West Nile virus being the other main issue around here - so mosquito control and avoidance are important. While you can never guarantee that you or your animal will not encounter a mosquito, various things can be done to reduce mosquito numbers (e.g. eliminating sites of standing water (which are mosquito breeding sites) wherever possible... swamps being a logical exception) and to reduce the risk of being bitten (e.g. avoiding high risk areas and times, long clothing, mosquito repellants). Vaccines are available for EEE and West Nile virus in horses (but not people), and the risk of these diseases should be considered when designing a horse's vaccination program.

Vesciular stomatitis in Colorado

Vesicular stomatitis (VS) has been reported in a horse in Las Animas County, Colorado. It's the first diagnosed case in the state since 2006, but it's not particularly surprising since this viral disease is periodically identified in horses in various parts of the US, and this case may be associated with northward movement of the virus from the Rio Grande River valley in New Mexico. However, it's noteworthy because VS is a potentially nasty disease and since it's also reportable, diagnosis of a case is accompanied by quarantine and other other control measures.

Vesicular stomatitis typically results in vesicles (small blisters) and ulcers in the mouth, on the tongue and lips, as well as on the udder (udder lesions are more common in cattle compared to other affected species). Lesions around the coronary band of the foot can also develop. Because of these blisters, infected animals may stop eating or drinking, and may be lame. It's a self-limiting disease, meaning it will typically resolve on its own, but animals can develop secondary problems like bacterial infections or severe foot damage, or in some situations the consequences of decreased drinking and eating may be severe, resulting in bigger or longer-term problems. A major concern is that this virus can also infect cattle and produce signs that are similar to the dreaded foot and mouth disease.

The source of infection in this case is not known, but the horse has no history of travel to areas where the disease is active, so insect-borne infection is suspected. That means that the virus must be present in other animals in the region, since blood feeding insects simply spread the virus around, they don't act as reservoirs or amplifiers of the virus. The farm is under quarantine and presumably surveillance is underway to identify other horses that have had contact with the animals on this farm, as well as to monitor for any more cases in the area.

When something like this occurs, travel restrictions for horses (and/or other species) are typically put in place by various governments, ranging from travel bans to requiring animals from areas where the disease is present to be accompanied by a health certificate saying that the horse has no signs of disease and hasn't be on a farm with the disease. Anyone planning travel to, from, or through, involved areas needs to be aware of this and check into transportation rules, including potential import restrictions if they want to enter Canada with a horse.

If you are in an infected region (or nearby), you can do some things to reduce the risk of your horse becoming infected by VS:

  • Restrict travel and avoid areas where the disease is active.
  • Avoid direct contact between horses as much as possible when visiting farms, shows or other places where horses mix.
  • Take basic insect control measures to reduce exposure to biting flies (e.g. black flies).
  • Avoid sharing/trading/selling tack and other items that have close contact with your (or any other) horse.

Vesicular stomatitis is zoonotic but it's of limited concern. Human infections are rare and usually just result in flu-like illness.

Horse shipping infections...are drugs the answer?

Sometimes, I get a little concerned when research papers get picked up by the press. It's not necessarily because the research is weak, it's just that results sometimes get overstated or misinterpreted when they work their way outside of scientific forums.

A paper published in the latest edition of the American Journal of Veterinary Research is one of those. The paper (Tsuchiya et al. 2012) describes a study that looked at the impact of interferon-alpha (used to stimulate the immune system) and enrofloxacin (an antibiotic) on body temperature and lung fluid white blood cell counts in 32 horses that were shipped for approximately 26 hours in commercial vans. Horses either received just interferon or interferon and enrofloxacin before being shipped.

  • After shipping, 3 antibiotic-treated and 9 untreated horses developed fevers. That's actually not statistically significant, by my calculations, and it's quite strange that the authors didn't do that analysis (and that the reviewers didn't pick that up).
  • Two antibiotic-treated and 7 untreated horses were treated with antibiotics after arrival because of concerns about infections. Again, that's not statistically significant and it's surprising (and concerning) no one pointed that out.
  • Overall, the average temperature of horses in the treatment group was significantly lower after arrival, but the clinical relevance of that is questionable since it was only a 0.4 C difference. Further, it's hard to say what a temperature immediately after arrival really means, since that's pretty early for a bacterial infection to have developed.
  • There were significant differences in tracheobroncial fluid (fluid collected from the airways) between the groups, with lower white blood cell counts in the treated group. That's an interesting finding and is consistent with less inflammation. What that means in terms of disease prevention is harder to say, but it's something worth investigating further.
  • There does not appear to have been any difference between the two groups in the ultimate health status of the horses.

This study provides some interesting information to help us think about how, when and why infections and inflammation develop after shipping. Results suggest that antibiotics might be useful in certain situations, but many questions remain. Any antibiotic use runs some risk of complications such as antibiotic-associated diarrhea. It also increases the risk of antibiotic resistance (and ultimately more problems trying to treat disease). We have to remember these issues when considering these results. Further, while it is typically much better to prevent disease than treat it, in situations like this, it's hard to say whether mass prophylactic treatment is actually preferable to early treatment, since horses can be observed closely after arrival and treated when early signs of disease develop. Ultimately, it's still not even clear from these data whether pre-treatment with antibiotics actually does have a positive clinical effect.

It's important to remember what this study tells us, and what it doesn't. Despite what some lay articles that have picked up the story say, it doesn't mean that antibiotics are broadly useful for keeping shipped horses healthy. The authors address this by stating "The use of enrofloxacin raises concerns regarding the emergence of antimicrobial-resistant bacteria, and it is important that antimicrobials such as enrofloxacin are not used inappropriately. The guidelines for enrofloxacin use in the Japan Racing Association’s medical office require that it is only administered as prophylaxis against transportation-associated fever when the duration of transportation is expected to be ≥ 20 hours and the horse has had clinical signs of transportation-associated fever before or is considered to be at risk for developing transportation-associated fever (eg, if the horse has undergone laryngoplasty or has a history of pneumonia)."

Regarding the big picture, however, this should make us think again about how we manage horses. Antibiotics should never be used as a crutch in place of good management. In a situation like this, where 19% of horses treated with interferon and enrofloxacin and 56% of horses treated with interferon alone get sick, something's wrong. Antibiotics may be an easy way to try to reduce the likelihood of disease in some situations, but that doesn't mean it's a good idea. Considering the number of horses that get sick (and die) every year from shipping-associated illness, maybe we need to rethink how they are transported. Is lack of antibiotics the problem, or is it how (and how long) horses are shipped? Maybe long, interrupted trips aren't a good idea, antibiotics or not.

Eastern equine encephalitis in South Carolina

'Tis the season...

As summer progresses, mosquito-borne infections become more common. While West Nile virus typically peaks later in the summer or early fall, Eastern equine encephalitis (EEE), a much more deadly viral neurological disease, tends to start cropping up earlier in the season.

Recently, EEE was diagnosed in two horses in Horry and Marion Counties in South Carolina, where the virus is mainly transmitted by a type of swamp mosquito, commonly known as the blacktailed mosquito. The outcome isn't stated in the report, but most likely the horses died, since mortality rates for EEE are extremely high.

Finding EEE in a region indicates that the virus is circulating in the bird and mosquito populations. Knowing this is important for a couple of reasons:

  • It means that horses might be exposed to the virus by mosquito bites. Therefore, it's a good idea to reduce mosquito exposure by a variety of methods. Vaccination also needs to be considered, but given the fact that vaccines don't protect horses immediately, waiting until the first cases of the year are diagnosed may be too late. Ideally vaccination should be performed a month or so before the time when exposure is likely.
  • It also means that humans may be exposed to the virus in the same way - by mosquito bites. EEE in humans is rare but devastating. If EEE is in an area, people need to take proper mosquito bite prevention measures. There's currently no vaccine against this virus for people. People cannot get EEE directly from horses or birds.

Horse owners need to be aware of infectious disease risks for their area (and anywhere they may take their horses), and they need to talk to their veterinarian about the risks and risk mitigation. Not every horse in North America requires EEE vaccination, but in some regions it's very important and should be a core vaccine.

More Queensland Hendra virus cases

While I guess it's getting beyond the point where Hendra virus infections in horses in Queensland, Australia are considered "news," it's still a highly concerning situation. Infections caused by this fruit bat-associated virus continue to occur in the region and there's no sign that this problem is going to go away any time soon.

In the latest report, two horses from a farm where a horse recently died of Hendra tested positive for the virus. In another location, a dog is being re-tested after a weak positive test. This situation brings back memories of the debate that occurred last year after a healthy dog that tested positive was euthanized as a precautionary measure, despite no information about whether the dog could actually be a source of infection.

Hendra is resulting in profound changes in the horse industry in Queensland. Beyond being a major problem in horses, this virus can be passed from horses to people, resulting is tremendous concerns amongst horse owners and veterinarians. Many veterinarians are refusing to work with horses because of the risk and I assume that some people are selling horses for similar reasons.

Infection control practices can presumably reduce the risk of transmission of Hendra virus between horses and from horses to people, but there's no way to completely eliminate the risk. Fruit bat control strategies get discussed, ranging from removal of fruit trees from horse pasture to reduce fruit bat exposure (logical) to fruit bat culls (highly unlikely to have any longterm effect). At a minimum areas under fruit trees should be fenced off from horses, and it has also been recommended to keep water troughs covered to prevent contamination with excrement from the flying foxes. Ultimately, everyone's holding out for an effective vaccine, which has yet to appear, but work on the vaccine is well underway and the hope is that a commercial vaccine could be released as early as next year.

(click image for source)

Horse smuggling

I’ve written before about infectious disease concerns associated with animal smuggling. It’s usually focused on the large-scale smuggling of reptiles, birds and other small critters, but it can happen in larger animals as well.

Some parts of the US/Mexico border appear to be rather popular smuggling routes for cattle and horses.  US Border Patrol agents recently seized 14 horses that were being smuggled into the US across the Rio Grande River, south of El Paso, Texas. USDA officials tested them for a range of diseases and found that all 10 adult horses were positive for equine piroplasmosis, a potentially fatal bloodborne parasitic disease. This is an important disease that’s common in Mexico but has been considered a foreign disease in the US (although recent recurrent outbreaks make it clear that it is established in some parts of the country). Regardless, smuggled horses come in with no testing, no documentation, not contact tracing and no controls, so they represent a great way to either bring in new diseases or spread existing ones around.

In 2011, approximately 280 cattle and around 160 horses (including donkeys and mules) were seized along the Rio Grande. I’m not sure what percentage of smuggled animals get caught. However, it’s probably a minority, so it’s likely safe to assume that lots of horses and cattle make their way into the US as illegal aliens and potential disease vectors every year.


Horse flu concerns at French show

Two horses have been removed from the showgrounds after testing positive for equine influenza virus at the FEI show jumping event in La Baule, France. The horses were not showing any signs of illness but were positive on PCR testing (presumably from a nasal or nasopharyngeal swab) and were sent home, along with four other horses taken care of by grooms of the two test-positive horses. Organizers are also planning to isolate all the horses that were in the same stable block as the positive horses, but they will stay on the showgrounds.

Authorities were monitoring horses at this show after a confirmed case of equine influenza was identified at a horse in another recent horse show in France. The article states that "precautionary testing on some horse was undertaken" but it's unclear how horses were selected for testing.  Was it random? Were horses that had been to the other show tested?  Had the horses tested been in contact with those other infected horses?

Testing of all horses is an aggressive (and expensive) approach, but equine influenza is an ever-present risk at shows and it's highly transmissible, so it may have been decided that the time and effort was worth it to test at least some of the animals.

The two positive horses were healthy and may not develop influenza. The test that was used is highly sensitive and detects viral RNA. That means if the test is positive there is actually flu virus present in the horse, as opposed to blood tests that detect antibodies to the virus, which simply determine whether the horse has been exposed. Viral PCR tests can also pick up dead virus, but it's unlikely that a horse would have RNA from dead influenza in its nose in the absence of an infection. 

Since these horses are currently healthy, there are a few possible explanations:

  • They are incubating flu and will get sick soon. Horses can start shedding the virus before they get sick, which complicates influenza control.
  • They could have had flu and recovered. However, since horses only shed the virus for a short time and it would be very unlikely for the horses to have been sick and recovered, and still be shedding the virus.
  • The horses might be infected but developed a very mild or clinically unapparent infection. They might have had enough inherent or vaccine-induced immunity to prevent disease from occurring but not enough to prevent the virus from growing. Flu vaccines are designed to reduce the incidence and severity of disease, not viral shedding,
  • It could have been a false positive lab test.

Is testing and exclusion of healthy test-positive horses overkill?

  • No, I don't think so. It's certainly aggressive, but it is a reasonable approach to dealing with a concerning and highly transmissible infectious disease, although even so it won't eliminate all infectious disease concerns. People whose horses are excluded probably don't like it, but hopefully they see the greater good, meaning "what goes around comes around" (or more specifically when dealing with disease control "what doesn't go around doesn't come around," and hopefully their horses will have a lower chance of being infected in the future because of similar measures taken by other people).

Vesicular stomatitis and Canadian horse import restrictions

The Canadian Food Inspection Agency has implemented import restrictions in response to diagnosis of vesicular stomatitis (VS) in a horse in Otero County, New Mexico.

Why the fuss?

VS is a viral infection that can affect a range of animals species. In addition to horses, it can infect cattle, pigs and sheep (and a few others). It produces painful blisters in the mouth and other areas that can result in decreased eating and drinking, lameness, severe weight loss and secondary infections. In food animals, it can cause severe economic losses. Another issue is that in cattle and sheep, it looks like the dreaded food and mouth disease. Lab tests can distinguish the two, but there can be a lot of angst when sorting out what causes vesicular diseases in cattle.

VS is a reportable disease in Canada and was last identified in the country in 1949. Import restrictions are a routine measure in response to the periodic US cases that occur.

In this case, the following restrictions have been implemented:

  • Horses cannot be imported from New Mexico.
  • Canadian horses that are in New Mexico must either get an import permit and supplemental USDA health certificate, or must be moved to another state for at least 21 days prior to returning to Canada. The supplemental certification indicates they've been evaluated by a veterinarian, have not been on a farm where VS was present over the past 60 days, and have a negative VS blood test. Horses that are moved to another state require a USDA certificate indicating that they've lived in that state for at least 21 days. (This may be complicated by restrictions implemented by other states on accepting horses from New Mexico.)
  • All other horses coming from the US must be certified by the USDA as not having been in New Mexico in the past 21 days.

Image: Ulcers on the tongue of a horse infected by vesicular stomatitis (VS) virus.  Image source: Colorado State University Extension

Botulism outbreak kills 23 horses

Botulism has been in the news lately, with numerous outbreaks involving different species and some human food recalls. Botulism outbreaks are often pretty dramatic because of the number of individuals that can be involved, the severity of disease and the fact that it's often difficult to do much beyond damage control once the problem is recognized. Recently, there have been reports of widespread duck deaths along with a couple of different recalls and warnings in Ontario about potentially contaminated smoked salmon and improperly eviscerated salted fish.

On the equine front, there's also been a large botulism outbreak that is believed to have killed 23 horses in Maine (USA). The outbreak occurred over the last month and, as is typical, has been devastating because of the profound susceptibility of horses to botulinum toxin and the inability to do much to save the animals once it was realized that botulism was present.

In adult horses, botulism is caused by ingestion of food that's been contaminated with toxins produced by the bacterium Clostridium botulinum, as it grows. This relatively widespread bacterium doesn't normally grow and produce toxins in horse feed since it requires an oxygen-free environment and other specific conditions, but when these occur, the incredibly potent neurotoxin can be produced. Equine outbreaks are often associated with haylage or silage (which if improperly fermented allow for C. bolulinum to grow) or contamination of round bales (e.g. an smaller animal that died of botulism gets accidentally incorporated into the bale, where the toxins can persist and/or the bacterium can grow if the right environment is present deep within the bale). In this outbreak, silage is suspected to be the cause. The silage is being tested to confirm this suspicion.

You can never 100% prevent botulism, since strange sources are sometimes found, but avoiding high risk feeds (e.g. silage, haylage, moldy round bales), trying to ensure that dead animals do not get caught up in hay bales during the baling process and taking exceptional care when baling if botulism is present in wildlife in the area can help greatly. A vaccine is available but it only protects against certain types of botulism. If those types are the main types that cause disease in a given area,  vaccination can be useful, but good feeding practices are the most important preventive measure.

Image: Horses at a round bale feeder (source:

Early West Nile virus case in Pennsylvania horse?

Local media are reporting an apparent case of West Nile virus infection in a horse in Northampton County, Pennsylvania. This is surprising since, while I know there are certainly mosquitoes emerging early with this mild weather, seeing active mosquito-borne infections at this time of year would be very unusual. That's particularly the case with West Nile virus, since it tends to be a late summer and fall disease based on the mosquito types that are predominant at that time of the year.

Information about this West Nile virus case is pretty sparse.  The report simply says the horse was euthanized because it was "suffering from the virus." Knowing if and how it was actually diagnosed is important to determine whether it was truly an active infection or a false-alarm, like this winter's report of West Nile virus in British Columbia.

Regardless, it's still a good reminder that we are now heading into the time of year when we have to think about mosquito-borne diseases in various species (including people). Measures to reduce mosquito populations, such as eliminating standing water (see picture), and mosquito bite avoidance are always good, regardless of what diseases are currently being diagnosed.

Image source:

Strangles outbreak at Saratoga

An outbreak of strangles (Streptococcus equi infection) has led to cancellation of the racing program at Saratoga Raceway in New York State. In a ripple effect, other racetracks in the region have taken measures to protect their horses, including banning horses from Saratoga, banning horses from surrounding tracks, not allowing horses that leave the grounds to come back and/or requiring that horses have a health certificate before entering the grounds.

As with most outbreaks, details are sketchy, including information about the number of exposed horses and specific outbreak response measures. Strangles is a highly infectious disease but it's also one that we know a lot about, and one for which containment of an outbreak is certainly possible with good infection control practices, screening to find carriers and a big dose of patience. Unfortunately, the latter is often the limiting factor, especially when money is on the line. The fact that Saratoga has initiated a quarantine and other tracks are taking precautionary measures is a good sign. Not long ago, most of these situations were met with silence and the hope that concealing the problem would make it go away (not usually an effective approach). We've come a long way in both our knowledge of strangles control and the industry's willingness to take control, so hopefully Saratoga (including officials and horsemen) is taking a good, evidence-based and patient approach to this outbreak.

Hitch-hiking mosquitoes and emerging diseases

Authorities in Hawaii are advising people in Oahu to eliminate standing water as a mosquito control measure. While it's always a good idea, it's of particular concern in this case bacause a rare type of mosquito, Aedes aegypti, was found around the Honolulu International Airport. This mosquito species is a highly effective vector for various infectious diseases, including dengue fever and yellow fever.

What does this have to do with companion animal disease? Well, nothing directly, but it's a good reminder of how infectious diseases can easily reach a distant area (even Hawaii) in a short period of time.

There are a plethora of mosquito-borne diseases out there, and presumably we don't even know about many of them. Mosquitoes don't fly very far, which helps contain these diseases to certain areas. However, mosquito-borne diseases can still spread over wide ranges if either the pathogen or the mosquitoes are hitch-hiking.

A common way for pathogens to travel is in various kinds of animals (especially birds) that can harbour the pathogen (usually a virus) and infect mosquitoes in distant areas.

Modern transportation can be an effective vehicle for pathogen-laden mosquitoes. Theoretically, all it takes is for a single infected mosquito to hop onto a plane and survive the flight to a new region. If the mosquito bites a susceptible host, it can cause a rare disease - that's of particular concern since it's unlikely that an exotic foreign disease in someone who has not left the country would be promptly diagnosed (and therefore promptly treated). Even worse, the disease could establish itself in the new region if a series of things happen:

  • The mosquito has to bite something or someone.
  • That something or someone has to be susceptible to the pathogen and that pathogen needs to grow inside the host's body to high enough levels that it can infect another mosquito.
  • Another mosquito that can carry the pathogen must come along, bite the infected individual and acquire the pathogen.
  • The new mosquito must then find another susceptible host to bite.
  • The above needs to be repeated enough times that the pathogen establishes a foot hold in the area and starts causing disease.

Is this common? No.

Is it possible? Yes.

West Nile virus is an example of what can happen. This mosquito-borne virus came out of nowhere in North America in the early 2000's and caused widespread illness and death in humans, horses and various other species. Did it arrive via a mosquito on a plane? No one knows, but it's certainly a possibility.

Botulism outbreak in horses

Botulism outbreaks in horses are usually bad news. Horses are very susceptible to botulism, and outbreaks in horses caused by contamination of food often end up killing multiple horses on a farm. The recent botulism outbreak in Reddington, IN is another reminder of how deadly it can be.

The outbreak involved a family that lost five horses to suspected botulism. "Suspected" because this disease can be hard to confirm sometimes, although it's usually possible to make a pretty solid presumptive diagnosis based on how the horses look and by ruling out the few other possible causes. The details are pretty sketchy. Apparently there are some other sick horses, but how sick they are and how many isn't clear.

Botulism occurs in two ways. In adult horses, it almost invariable occurs after ingestion of the extremely potent botulinum toxin produced by the Clostridium botulinum bacterium. In foals, it usually occurs after ingestion of the bacterium, which then produces toxin in the foal's intestinal tract.

In adults, outbreaks are usually associated with contaminated feed.  There are some high-risk feeds like haylage and silage (see photo) that we usually focus on first, but sometimes botulism toxin can be found in hay or other common feeds. Haylage, silage and other fermented feeds become a problem with they are improperly fermented, allowing the Clostridium botulinum to grow and produce its toxins. Sometimes, contamination of feeds can occur when an animal that has died of botulism (and has the bacterium and its toxins in its body) gets incorporated into hay or other feedstuffs.

When an outbreak is suspected, a key step is removing any potentially contaminated feeds to reduce further exposure, although often it's too late by the time the disease is recognized. Antitoxin (which is pre-formed antibodies that help neutralize the botulinum toxin) can be given to exposed horses, but it's extremely expensive and does not reverse any damage that's already been done. That's why these outbreaks are often so disasterous, because when the diagnosis is made the only thing left to do may be damage control to try to save some of the less affected horses. That's tough because botulism has a very high mortality rate in horses.

The farm owners in Reddington are urging local horse owners to be on the lookout for botulism. It's reasonable, but rarely do we see multi-farm outbreaks from botulism. They also state that botulism doesn't affect cattle, which is wrong. Cattle are more resistant than horses, but they certainly can get botulism.

A botulism outbreak in horses poses little risk to people. People are susceptible to this horrible disease as well, but to get it someone would have to ingest the same contaminated feed that the horse did. There's no risk of transmission of botulism from an infected horse to a person or another animal.

California equine event biosecurity document

In response to the large and high-profile equine herpesvirus outbreak that occurred last summer, the California Department of Food and Agriculture has published a Biosecurity Toolkit for Equine Events. It's a nice, comprehensive document that goes over a wide range of things that can be done to reduce the risk of disease transmission at horse shows and similar events, and is one of the better resources available on the subject.

As I've said before, I don't use the term "biosecurity" for equine events since I think it's a fallacy. Biosecurity involves keeping infectious agents away from a group of animals. You can do that on a chicken farm, where you bring in a bunch of chicks at the same time, house them under tightly controlled conditions, keep people away, don't let them near any other birds, send them to slaughter all at once, and then disinfect the place before starting again. With horse events, we create absolutely beautiful conditions for infectious diseases to be introduced and transmitted. For example:

  • Many horses from many different areas with different health statuses are mixed together.
  • Vaccination requirements are often sparse to non-existent.
  • Horses have a high likelihood of direct and indirect contact with each other.
  • Healthy horses can carry a variety of infectious agents.
  • People often bring horses that they know are or have recently been sick, and there's little scrutiny of arrivals to detect any infectious horses.

So, for me, we instead deal with infection control when horses are involved, whereby we try to reduce (but know we can never eliminate) the risk of infectious diseases and outbreaks.

Is it just a matter of semantics? To a degree, yes, and maybe it's just the Professor side of me coming out. At the same time, I think it's important to consider the difference since we have to acknowledge the inherent risks that come with showing horses, think about the risks involved with different situations and come up with practical ways to reduce those risks as much as possible.

Good infection control practices for equine events, with measures taken by both organizers and attendees, are a good start.

Photo credit: John Goetzinger (click for source)

Rabid horses in Tennessee

Rabies is pretty rare in horses in North America, with only 37 reported cases in the US in 2010 and 1 in Canada in 2011 (the latest years for which data are available). So, finding two apparently unrelated cases of rabies in horses in the same area in the same month is pretty unusual and concerning. Yet, that's what's happened in Tennessee, where rabid horses were identified in both Rutherford and Marshall counties in January.

Little information is available about the cases, but both were identified as having the skunk rabies virus variant. That doesn't necessarily mean they were infected by skunks (since other species can be infected by this virus variant) but it is suggestive, and indicates that rabies must be active in the skunk population in that region.

Regardless of the source, these cases are a reminder of why rabies vaccination of horses is important, and why rabies vaccination is considered a "core" equine vaccine by the American Association of Equine Practitioners. Rabies is invariably fatal in horses and it's also a major public health risk. While I've been unable to find confirmed cases of horse-to-human rabies transmission, it's a possibility, and additionally, rabid horses have killed people because of their unpredictable and aggressive behaviour.

Vaccination is cheap insurance against rabies - it's never a 100% guarantee, but it's a whole lot better than without vaccination.

(click image for source)

Tropical Rhodococcus equi outbreak? has reported on an outbreak of Rhodococcus equi that has claimed the lives of seven ponies at an equestrian facility on the island on Mayotte (a French protectorate off the coast of Madagascar). Local agriculture officials report that two other horses are also affected, but recovering, and the facility has been quarantined

There are a few strange aspects of this report. Rhodococcus equi is an important cause of respiratory disease in foals, in which it can cause serious abscesses in the lungs. However, it's extremely rare in mature horses, and it seems that the horses affected in Mayotte were adults. It's not impossible, but an outbreak of Rhodococcus in adults would be incredibly surprising, indicating either something that made these horses remarkably susceptible to the bacterium, or the presence of a strain of Rhodococcus more able to cause disease in adults. A more likely explanation is that it's not actually Rhodococcus. There's no mention of what type of disease the horses had or for what other infectious agents tests were done. A Department of Agriculture official stated that the diagnosis was made by blood tests, but blood testing is pretty useless for diagnosis of Rhodococcus. So, I'd consider the diagnosis highly questionable without further information.

Whatever the cause, something that kills seven horses on a farm is remarkable and thorough testing is needed to determine exactly what's happening. In the unlikely event that this was caused by Rhodococcus, more work needs to be done to explain why the outbreak occurred and why it was so severe. If (as is likely) it wasn't Rodococcus, knowing the actual cause is important for controlling further spread and preventing problems in the future.

Fortunately, the remote nature of this location makes it rather unlikely that whatever's happening there will spread to another region soon.

Image: Location of Mayotte (click image for source)

Ontario equine biosecurity seminars

Equine Guelph has announced a series of equine biosecurity workshops across Ontario which will take place during the month of March 2012. The sessions are free to attend and will focus on how to apply basic and practical concepts of infection control to reduce the risk of disease exposure and outbreaks in horses of all types. The workshops are part of a broader Beat the Bugs biosecurity program being organized by Equine Guelph, which also includes a two-week e-session being offered in April 2012.

More information about the workshops (including dates and locations, and to register), e-session and the Beat the Bugs program can be found on the Equine Guelph website.

Methicillin-resistant staph...What's in a name?

I've written about this topic before, but it's an important (and increasingly common) issue to understand, so bear with me while I address the subject again.

I typically get multiple case consults in person, by phone or by email about methicillin-resistant (MR) staphylococci every day. A lot of these start with "I have a case with an MRSA infection..." While trying not to be rude, I tend to interrupt the conversation at that point with "Is this actually Staph aureus or another staph?"

I do this for a few reasons:

  • A few years ago, the vast majority of "MRSA" infections in dogs, cats, horses and other companion animals were actually MRSA - that is methicillin-resistant Staphylococcus aureus. However, in the past few years, there's been a tremendous upsurge in other MR-staph, particularly booming numbers of MR-Staphylococcus pseudintermedius (MRSP) infections in dogs. These days, if it's a dog or cat, when I ask the "What staph is it?" question it's usually not actually MRSA. We're  starting to see more MRSP in horses too, complicating things in that species as well.
  • Staph are divided into two groups, coagulase positive species (which include S. aureus and S. pseudintermedius) and coagulase negative species. The coagulase negative species are commonly found in or on healthy animals and are often methicillin-resistant, but they are not very virulent and don't usually cause disease outside of very high risk populations (e.g. very sick animals in a veterinary hospital). If a MR coag-negative staph is isolated, I am far from convinced it's the culprit, and typically the real cause of the problem still needs to be found.
  • MRSA is much more of a concern from a public health standpoint, as it can move between animals and people. While MRSP can cause human infections, these are extremely rare.
  • MRSA is not really adapted to live in dogs, cats, horses and many other animals. It can, for a while, but doesn't do so longterm, and the vast majority of MRSA carriers will get rid of it on their own. In contrast, it appears that MRSP (at least in dogs) can stay with the animal for a very long period of time. Therefore, an animal that has had an MRSP infection has a reasonable chance of shedding the bacterium for a long period of time, which might be of relevance for its health in the future.
  • The two main MR-staph of concern in companion animals are MRSA and MRSP. Some diagnostic labs still don't try to differentiate the two, despite the fact that there are different guidelines for determining whether they are methicillin-resistant. If someone has a result that doesn't differentiate MRSA from other staph, I tell them their lab isn't doing things right and they need to talk to them so they can have confidence in the results.

More information about MRSA and MRSP can be found on the Worms & Germs Resources page.

BC's not-so-West Nile case

Following reports of a veterinarian warning colleagues and horse owners about West Nile infection in a British Columbia horse, Dr Brian Radke, a Public Health Veterinarian at the BC Ministry of Agriculture, has clarified the situation.

"The BCCDC co-ordinates WNV surveillance for the province of BC including monitoring of mosquitoes, birds, horses and humans. The BC Ministry of Agriculture supplies information to BCCDC on horse cases. In Canada, equine cases of WNV are reportable the Canadian Food Inspection Agency (CFIA).

The CFIA has no reports of WNV consistent with the Prince George horse. Discussions with the veterinary practitioner have clarified that the horse's illness, which occurred in November, was not due to WNV.

The testing discussed in the article was not conducted at the provincial government animal health laboratory. The BC Ministry of Agriculture is following up to determine the nature of the WNV testing and the appropriate interpretation of the test results.

BCCDC WNV surveillance indicates the following:

  • In 2011 no humans, mosquitoes, or birds were detected with WNV infection in BC. One horse in the Central Okanagan was reported as positive and that report is under review.
  • There have been no positive WNV indicators in the Prince George area.
  • In BC, WNV has been detected in southern parts of the province, all below N50 latitude. (By comparison, Prince George is N54 latitude.)
  • Risk modelling by BCCDC suggests that Northern BC, including Prince George, experience insufficient sustained heat during the short summer for WNV to amplify and be transmissible by the low density of vector mosquito species.
  • The risk modelling also suggests that even in the warmest (that is, southern interior) areas of the province, the risk of WNV infection decreases significantly in September as the vector typically ceases seeking blood meals.

The BC Ministry of Agriculture and BCCDC look forward to working with the province's equine practitioners to interpret WNV testing results and epidemiology to assess the risk of WNV to horses in the various regions of BC. The assessment of risk could then inform decisions about the appropriate interventions for WNV infection in horses in the various regions."

We thank Dr. Radke for the information.

West Nile warning for BC horses

A Prince George, British Columbia veterinarian is warning other veterinarians and horse owners about West Nile in the province. Little information is available at this point, but the warning is in response to a diagnosis of West Nile infection in a horse from the area. The report calls it a "deadly disease" but it would be more appropriate to call it a "potentially deadly disease," since most horses that are exposed don't get sick, and many sick horses recover. I don't want to downplay the seriousness of West Nile, but it's important to keep it in perspective and make people panic.

The BC CDC has an ongoing West Nile surveillance program because of the obvious concern as this virus has worked its way across North America over the last decade. While it's taken it's time getting to BC, West Nile virus has been identified in the province, and only time will tell whether it becomes a serious health concern for horses or people. The latest update of the BC CDC surveillance data indicates one positive horse, but no positive humans (of 415 tested) or mosquito pools (2282 tested). The one equine case that was documented was from Central Okanagan. The horse had clinical signs consistent with infection, although the severity and outcome are not reported.

It's unclear to me whether this Prince George case is something that's happened just recently or whether the horse was sick. It's pretty late in the year for a mosquito-borne virus, but not impossible in some areas.

Does this report mean that horse owners in BC should be concerned?  Maybe. "Aware" might be a better term.

Horse owners and veterinarians always need to be aware of the infectious disease risks in their area, and areas to where a given horse may travel. Keeping apprised of ongoing West Nile virus surveillance can help determine the likelihood of exposure, but that doesn't mean you can wait until there's a case next door before you do anything. (Someone has to have the first case in an area, and you don't want that to be you.)

Whether or not to vaccinate against this virus depends on the likelihood of exposure and risk aversity. Available vaccines are rather safe and effective (not 100% on either account, like any vaccine, but quite good overall), and vaccination decisions should be made based on a well-reasoned discussion between veterinarian and owner, considering a variety of factors such as where the virus has been found and how much risk everyone is willing to take.

The news report has a quote recommending vaccination in the spring. That's the typical time people vaccinate against mosquito borne diseases, but that's not my recommendation. For me, the goal is to vaccinate so that peak immunity is present at the time when exposure is most likely. West Nile virus is classically a late summer/fall disease, based on mosquito types and their biting patterns. For that reason, I like to see horses vaccinated a little later in the year - closer to the high risk period. Again, it's important to know disease trends in each region to make the most informed decision.

So, horse owners in BC should be aware but not panic. A good discussion about vaccination and about general mosquito avoidance practices should be the first thing that happens.

Murray Valley Encephalitis down-under - Help from the chickens

Although the weather in Southwestern Ontario seems quite confused lately regarding whether it wants to be winter or spring, at least we're still a few months off from having to worry about mosquitoes and the viruses they carry once again.  Warmer parts of the world, however, are in the midst of their mosquito season, and some chickens are lending a hand to give people in the area a "heads up" about what's around.

The Health Department of Western Australia has detected Murray Valley encephalitis virus (MVEV)  in chicken flocks in East Kimberley.  The department has also tested and found the virus in its sentinel chickens in Wyndham and Kununurra.  These sentinel birds play an important role as an early warning system when viruses like MVEV are circulating in the area.  Just like West Nile virus, MVEV typically circulates between birds and the mosquitoes that like to feed on them, but problems occur when the same mosquitoes start to bite people (or other susceptible animals such as horses), particularly when there are a lot of mosquitoes, like when the weather is very wet or when there's been flooding.  Although most people who are infected with MVEV or WNV fight off the virus with no difficulty, or may simply develop short-term, non-specific signs of illness like mild fever and malaise, in some people these viruses can cause severe infection of the brain (encephalitis) and may even be fatal.

Knowing that MVEV has been found in these "guardian" chickens lets people know (via warnings issued by the health department) to take extra precautions against mosquito bites, such as:

  • Staying indoors during peak mosquito activity - dusk and dawn
  • Wearing protective clothing including long-sleeves and long pants
  • Applying insect repellent

In North America, you can pretty much substitute West Nile for Murray Valley in a case like this.  Sentinel chickens have been used to provide early warnings of circulating WNV here, before cases are detected in people or horses.  Another means of early detection that is also used is testing pools of mosquitoes directly.

It just goes to show you can still be an important part of the country's defenses, even if you're a little chicken :p

(click image for source)

Headshaking and equine herpesvirus

Headshaking is a frustrating problem in horses. It's often hard to identify a cause and treatments are frequently unrewarding. Many different possible causes of headshaking have been proposed, including equine herpesvirus type 1 (EHV-1) infection.

As is common with herpesviruses, EHV can lie dormant in the body, and it may be re-activated during times of stress. There's ample evidence that other herpesviruses can cause nerve pain with reactivation. In humans, re-activation of the varicella-zoster virus (the herpesvirus that causes chickenpox) causes shingles, which is a very painful disorder. Since dormant EHV-1 can be found in nerves in a horse's head, it has been suggested that pain caused by reactivation of dormant virus could be a trigger for headshaking.

A recent study published in the Journal of Veterinary Internal Medicine (Aleman et al 2011) investigates this theory. The researchers looked for the presence of EHV-1 in trigeminal ganglia (a group of nerve "nodes" in the head) in headshaking horses and healthy controls. While it was only a small study, there was no evidence indicating a role of EHV-1 in headshaking, since the virus was only detected in 1/8 headshakers compared to 0/11 controls.

This study doesn't absolutely rule out EHV-1 as a cause a headshaking, since it still could be one of many potential causes that is involved in only a minority of cases. However, this study suggests that EHV-1 is not a particularly common cause of headshaking, if it causes it at all.

Bat slaughter = Hendra virus control?

Bob Katter, an Australian Member of Parliament and leader of the Australian Party, has proposed culling flying foxes (fruit bats) as a way to control Hendra virus, which is spread by these large Australian bats. He's not the first person to make such a proposal, but it's a knee-jerk reaction that in reality doesn't make a lot of sense.

It's not completely clear whether Mr. Katter is proposing a plan to completely eradicate the flying foxes altogether, or to simply let people kill any such bats they find on their property, but neither approach is likely to be effective in terms of decreasing the risk of Hendra virus transmission.

If people kill flying foxes on their property, they'll just be replaced in short order by bats from neighbouring areas.

Trying to eradicate the entire species is a bad idea for a variety of reasons:

  • Tinkering with a complex ecosystem doesn't often turn out the way you want it to. Australians certainly know from past experiences that bad things can happen when new species are introduced (rabbits are just one example). The same might happen when a species is removed.
  • Eradication of the species is probably impossible or at least very difficult. I don't know much about the reproductive rate of flying foxes, but if the species can reproduce at a reasonable rate, they can probably replace the culled animals unless people are really aggressive and seek out all remote breeding sites. The limitations of culling have been clearly shown in rabies control, where it doesn't do much because culled dogs are quickly replaced by new dogs.
  • Eradicating flying foxes would be very expensive. What could that money do if put into research on vaccination, treatment, and other worthwhile ventures? What if efforts were focused on eliminating flying fox roosting sites in horse pastures? Overall, the impact would probably be much greater.

Why stop with flying foxes? Australia has lots of nasty critters, ranging from spiders to saltwater crocodiles. Should we kill all of those too? Dog bites kill more people than Hendra every year. Should we kill all dogs?

Hendra virus is not something to ignore. While infections in horses are rare, they are usually fatal and there's the risk of transmission to people. Human infections are very rare but often fatal. So, ways to reduce infection of horses as a means of reducing both human and horse disease are important, but the slaughter of flying foxes doesn't make a lot of sense.

Bad 2012 for Hendra virus in Australia

While you don't want to read too much into a single case, 2012 has started off in a bad way for Queensland horses. Hendra virus was identified in a Townsville area horses that died.  This zoonotic viral disease is  largely restricted to Queensland, Australia, but it has a high fatality rate in horses (and people). Hendra virus is spread by fruit bats and is an ever-present concern to Queensland horse owners and veterinarians, but a mid-summer infection is quite unusual (remember that it's currently mid-summer in Australia). Most cases tend to occur from July to September - this case is a reminder that seasonal trends are just that: trends, not absolute rules.

Fortunately, the attending veterinarian used proper precautions when handling the horse to limit the risk of zoonotic transmission of Hendra virus. However, there will presumably be an investigation to determine who had contact with the horse and their potential for exposure. There is currently no way to prevent or specifically treat Hendra virus infection. An experimental antiviral treatment has been tried in the past, but it's effectiveness if far from clear.

Last year was quite bad in terms of the number of Hendra cases that were detected in Australia. Let's hope this early 2012 case isn't a sign of things to come.

Horse rabies in Florida

Marion County (Florida) public health personnel recently issued a rabies alert after a horse in the area tested positive for the virus. It’s a standard alert, emphasizing avoiding contact with wildlife, reducing things that attract wildlife to houses (e.g. accessible pet food or garbage) and recommending vaccination. Interestingly, while this alert was prompted by a case of rabies in a horse, it only mentions vaccination of dogs, cats and ferrets. That may have been because it was an off-the-shelf alert, not really tailored to this situation, but it shows how horses can be overlooked when it comes to rabies.

Fortunately, rabies is a rare disease in horses. In 2010, there were 37 reported cases of equine rabies in the US and only one in Canada (two Canadian cases have been identified so far this year). That’s a very low rate, especially considering the number of horses out there, but it’s still more cases than there should be for a very serious yet highly preventable disease.

Unfortunately, rarity sometimes breeds complacency, so despite the fact that rabies is invariably fatal in horses and rabid horses pose a risk to people, vaccination of horses is often overlooked. While rabies is rare in horses, rabies vaccination shouldn’t be rare. Every horse in a rabies endemic region (or that might be traveling to such a region) should be vaccinated against rabies. It’s cheap insurance against a very dangerous and deadly disease.

Pigeon fever in Louisiana horses

Pigeon fever is an equine disease that doesn't have anything to do with pigeons. It's an infection caused by the bacterium Corynebacterium pseudotuberculosis which results in the formation of abscesses, usually along the chest (pectoral region) and lowest part of the abdomen. The name "pigeon fever" comes from the swelling in the chest region that vaguely resembles a pigeon-breast. A recent report describes and outbreak of pigeon fever involving at least 30 horses in Louisiana, bringing the estimated number of cases in the state in 2011 to over 100.

Pigeon fever is a regionally (and to a lesser degree seasonally) variable disease. It predominantly occurs in California, but over recent years it has expanded its range in the western US, and from this report, it's obvious that it has a good foothold in some other areas in the south east as well.

Corynebacterium pseudotuberculosis lives in the soil, and causes infections in horses when it gets inoculated under the skin via wounds and perhaps sometimes through fly bites. Once it gets into the tissues, it starts to grow and causes painful (and potentially large) abscesses that often need to be surgically incised in order to drain them.

Infection control practices on farms can help reduce transmission of the bacterium between horses and to reduce the risk of injuries. These include:

  • Quarantine of new arrivals and careful inspection for sign of infection.
  • Isolation of known infected horses.
  • Use of "contact precautions" when dealing with infected horses to prevent transmission of the bacterium via peoples' bodies or clothing. This involves the use of protective outwear (e.g. coveralls and boots that are only used for the infected horse(s)) and gloves.
  • Proper use of handwashing / hand sanitizer by people handling infected horses (or any horses, really, from a broader standpoint).
  • Prevention of cross-use of items like buckets between infected/quarantined horses and the general horse population.
  • Use of fly repellent, especially on horses with open wounds or draining abscesses.
  • Careful cleaning and disinfection of areas potentially contaminated by pus from draining abscesses.
  • Inspection of stalls, paddocks and fields for things that could cause wounds that might subsequently become infected.

Pigeon fever is a good example of why it's important to know disease patterns in your region (and those to where your horses travel). Being aware of the possibility of a specific disease is an important step in diagnosis, and knowing there is disease activity in any area in which your horse may have been is a key part of that. This disease is also an example of why we need ongoing disease surveillance and reporting, because if a disease makes it into new regions, veterinarians and horse owners need to know about that as soon as possible to allow for quicker diagnosis and use of control measures. Unfortunately, organized disease surveillance and communication is sorely lacking in horses.

Photo: A Jiennense Pouter Pigeon, which has a very pronounced breast compared to other breeds.  The swelling of a horse's pectoral region due to abscesses caused by C. pseudotuberculosis is the reason the disease is sometimes called "pigeon fever." (click image for source)

equIDblog has moved to Worms & Germs!

Unfortunately, because of funding challenges (translation... there was no more money), we were no longer able to maintain our equine infectious disease blog (equIDblog) as a separate site. However, based on the positive feedback we had and the amount of traffic on the original site, we still think it serves a role and are dedicated to maintaining equIDblog in some form. So, we are going to merge equIDblog with the Worms & Germs Blog. We have already moved the equIDblog Resources page, which can be accessed through the link in the title bar.  We will also gradually move all of the current archived blog posts from the site and place them under the equIDblog topic category which can be found in the left index bar.  Here we will maintain all of the site's current content and continue to provide information and commentary on equine infectious disease issues. Thanks to all of our loyal equIDblog readers for making the blog such a success, and we hope you'll continue to follow us here on the Worms & Germs Blog!

Beat The Bugs: New Biosecurity Venture For Equine Guelph

Equine Guelph has received funding for Beat the Bugs, a new equine biosecurity venture. The program has been funded by the Agricultural Biosecurity Program, a Canadian federal-provincial-territorial initiative.

From ongoing cases of strangles to large outbreaks of EHV, it's abundantly clear that infection control is a critical area for the equine industry, and one that typically receives little attention in the absence of an outbreak. The new Beat the Bugs program will be launched in March 2012, and will facilitate development of farm-specific biosecurity programs through workshops and a two-week online program. The program is being developed by Equine Guelph with the cooperation of various academic and industry partners. More information can be found on the Equine Guelph website.

Study Seeking "Superbugs" In Horses

A two-part study (Maddox et al. 2011) was recently published online in the Equine Veterinary Journal looking at antimicrobial resistant "superbugs" in horses in the UK.  The first part of the study had the simple objective of estimating the prevalence of both MRSA nasal colonization and fecal shedding of antimicrobial resistant E. coli in the UK horse population. The reason they were looking at E. coli is because this bacterium is part of the normal intestinal flora of most animals (including horses), so it's easy to find, and it is frequently exposed to antimicrobials whenever a horse is treated systemically (i.e. with either oral or injectable antibiotics), so researchers use it as an "indicator" for resistance that may develop in other bacteria as well.  E. coli doesn't typically cause gastrointestinal disease in horses like it can in people, nonetheless E. coli is a common cause of uterine, urinary and wound infections in horses, as well as septicemia in foals, and antimicrobial resistant infections in these situations can certainly be a big problem.

Out of 678 nasal swabs (taken from horses on over 500 premises), only 4 (0.6%) were positive for MRSA.  That's good to see, as it's very easy for MRSA to spread in a horse population "under the radar," because colonized horses do not have any outward signs that they are carrying the pathogen.  The overall low prevalence in the community setting is similar to previous community studies in the UK and other areas.  Out of 650 fecal samples, 452 (72.2%) were positive for an E. coli that was resistant to at least one antimicrobial.  That's not too surprising.  The bigger concern is that 233 (37.6% - over one third of all horses tested) samples contained multidrug-resistant E.coli (defined in this study as resistance to more than three antimicrobial classes) and 42 (6.3%) samples contained an E. coli that produced an extended-spectrum beta-lactamase (ESBL).  ESBLs are particularly problematic because they can be relatively easily transferred between bacteria, they confer resistance to a large number of commonly used antimicrobials in the beta-lactam class (which includes penicillins and cephalosporins), and are frequently associated with genes that confer resistance to other antimicrobial classes as well.  Bacteria that produce ESBLs are a significant problem in human medicine and have been reported to cause infection in horses as well.

The second part of the study used information collected from questionnaires filled out by the horse owners to try to determine risk factors that affected the odds of a particular horse shedding antimicrobial-resistant E. coli.  They used some pretty heavy-duty statistical analysis because they were looking at so many factors and different outcomes, and any time that happens you have to take the final numbers with a grain of salt. Nonetheless, the results can help point the way for future studies to help determine which factors may have the biggest impact on the risk. The authors found recent hospitalization and veterinary treatment for various conditions over the last six months were associated with higher odds of shedding multidrug-resistant strains of E. coli, and the type of farm/facility also affected the odds.  In addition, having a recently hospitalized horse on the premises (among other things) increased the odds of a horse shedding ESBL E.coli.

What does all this mean for the average horse owner?  The results really aren't new or startling.  We already know that antimicrobial resistance is a growing problem in equine medicine, as it is in veterinary and human medicine in general, and this is one more set of studies that provides evidence to that effect.  I have no doubt that if a similar study was performed in North America the same kinds of resistant bacteria would be detected, although the numbers may vary somewhat one way or another.  The second part of the study also re-emphasize the role that antimicrobial use plays in promoting development of and selection for resistant bacteria, and the potential for the treatment of certain horses to affect the microbes being carried and shed by the animals around them.  In the end, it comes down to being responsible about how we use antimicrobials in order to curb the development of resistance, so that these important drugs remain effective for treating serious infections in the future.  This applies equally to their use in people and animals of all kinds.

Botulism Suspected In Aussie Outbreak

A couple of days ago, I reported about a deadly outbreak on a Queensland farm that had killed a significant number of horses. A definitive diagnosis has still not been made, but it is starting to look like botulism might be the cause. In my previous assessment, I said botulism was a potential cause of an outbreak like this, but that this particular disease has a pretty consistent clinical presentation so it was probably unlikely if no one was talking about it as a leading option. It looks like now they are, with the owner stating "I've been talking to vets all over Queensland and they're saying the symptoms are spot-on for botulism." It's unclear whether the first vet(s) didn't consider it or whether there wasn't much veterinary involvement at all initially. Regardless, botulism makes sense, particularly with the description of the type of illness that's now being provided.

Botulism testing is underway, but it's often hard to get a positive lab test for this disease in horses. Often, it's a presumptive diagnosis made based on the clinical appearance and lack of any other identifiable cause. Botulism outbreaks on horse farms can be devastating, as in this case. They are often associated with feeding improperly fermented silage or haylage, but there are a variety of ways horses can ingest feed (or water) contaminated with the toxins produced Clostridium botulinum.

The good thing that comes out of this, if botulism is diagnosed, is that there's not much risk to other horses in the region, or at least not any higher risk than is always present. Whenever a large number of horses die from an unknown cause, it's always a concern that a new disease might be involved, something that fortunately does not seem to be likely here.

Image: Poor tongue tone is one of the classic signs of botulism in horses, which results in difficulty eating and drinking (click image for source).

Who's Better At Biosecurity?

There are a lot of recommendations out there for establishing or improving sound infection control practices on horse farms, many of which can be found on this very blog.  Some refer to such practices as "biosecurity," but what's done on horse farms compared to the often very strict biosecurity protocols at facilities such as swine or poultry operations (e.g. all-in all-out management, closed barns, shower in) is very different, so we prefer to call it an infection control program, rather than "biosecurity."  Regardless, one of the biggest challenges with regard to infection control, in almost any setting, is getting people to comply with all the various policies and recommendations.  Unfortunately, it's not enough to just tell people what needs to be done (that'd be too easy!) - knowledge by itself usually won't change people's behaviour.  They also need to be motivated to change their behaviour, for example by the potential for a positive reward (e.g. they get to take their horses to shows) or the potential to avoid a negative outcome (e.g. their horses don't get sick).  Furthermore, individuals need to really believe they are capable (physically and mentally) of performing the required tasks - if they don't think they can do it or be effective at it, they're unlikely to try.  In reality, getting people to change their behaviour to adopt sound infection control practices can be quite complex.

A study soon to be published in Preventative Veterinary Medicine (Schemann et al. in press) looked at some of the factors that affect horse owners' biosecurity practices and perceptions.  The study was performed in Australia one year after the devastating equine influenza outbreak that occurred in 2007, using an online questionnaire to which 759 horse owners responded.  Each owner's biosecurity compliance was rated as low (30%), medium (20%) or high (50%) based on how often they reported using 16 different infection control measures.

Factors that were associated with low compliance or poor biosecurity practices included people who:

  • were younger in age
  • had two or more children
  • were not involved with horses commercially
  • had no long-term business impact from the 2007 equine flu outbreak
  • were not fearful of a future outbreak of equine flu in Australia
  • thought their current hygiene and access control practices were not very effective in protecting their horses

Now, studies based on surveys of this kind always need to be taken with a grain of salt, as the study population itself was difficult to define and the information was all self-reported by owners, which can lead to confounding and misclassification bias.  Nonetheless, the results are still interesting and on the whole are consistent with behaviour theory.  Those whose income and livelihood were not dependent on the horse industry, and those who were not fearful of another outbreak, would be less motivated to put the effort into infection control measures.  Furthermore, those who felt that what they were doing already wasn't really effective (for whatever reason) would be less motivated to try harder because they can't see the benefit.  It's quite possible (as the authors speculate) that having two or more children results in less compliance with infection control simply due to the time constraints associated with having kids.  Lack of time to properly perform infection control procedures is a major barrier to compliance, even in human hospitals, particularly with understaffing issues. The lower compliance among young people is also common to studies looking at protective behaviour in human health, possibly because young people have a sense of certain degree of invulnerability that results in riskier behaviour overall.

When it comes to infection control, the old adage "a chain is only as strong as its weakest link" is very important to remember.  Although 50% of the horse owners in this study reported having high biosecurity compliance, the 30% with low compliance could ruin all their efforts should another outbreak occur, by contributing to the transmission and propagation of the disease on their own farms as well as to others.  Hopefully this study will help the horse industry and government identify specific groups (i.e. young people, those not financially dependent on horses) at which educational and motivational campaigns can be targeted in the future.

Another EHV-1 Equine Hospital Quarantine

Once again, an equine hospital is under quarantine because of equine herpesvirus type 1 (EHV-1). There have been a number of such incidents this year, highlighting both the increasing concern with this important pathogen and perhaps more transparency and willingness on the part of hospitals to take aggressive infection control measures when it is detected.

The latest incident involves the University of Tennessee Equine Hospital. The entire situation is related to identification of EHV-1 infection in one horse that was admitted on September 15 and euthanized a few hours later because of severe and progressive neurological disease. The next day, the Tennessee state veterinarian implemented a seven-day quarantine, while the hospital voluntarily implemented a 14-day quarantine. Seven days is pretty short and if you're concerned enough that you think quarantine is needed - if it's going to be done at all, it should be done right (i.e. for longer than a week).

At last report, there was no evidence of transmission to other horses.  Presumably university personnel are closely watching horses in the hospital and are hopefully  in contact with people who had horses they after the EHV-1 horse was admitted but before quarantine was implemented.

The need for facility closure or quarantine is always something of debate. EHV-1 should be a containable problem with prompt recognition of affected horses, proper isolation facilities and compliance with infection control procedures. Identifying infectious horses is a key aspect, as they are not always screaming "I have EHV!" when you see them. If a horse with EHV isn't identified as a potentially infectious animal and isolated from the start, the risk of transmission goes up. In this case, it was stated that the horse was kept in a "separate area of the equine hospital." It's not clear whether this was in an isolation unit or not. If it was admitted directly to isolation and was handled with appropriate protocols, the risk of other horses being infected should be very low. Given the time frame involved (it was only in the hospital for a few hours), even if it was in the main hospital, the likelihood of transmission to other horses is probably still relatively low, but it's certainly possible.

From a disease control standpoint, it's much better to be overly aggressive at the start while you are sorting out what's going on rather than sitting back and hoping for the best. While this often results in negative publicity, it's better than ending up with an outbreak which results in even worse publicity, as well as more sick animals.

EPM Testing

Equine protozoal myeloencephalitis (EPM) is a frustrating disease. It's been referred to as one of the most overdiagnosed, underdiagnosed and misdiagnosed equine diseases - an apt description. In some areas, every horse (particularly every racehorse) that has any real or perceived abnormality (such as not running fast enough) gets treated, usually without any attempt to make a true diagnosis. Most of these animals don't have EPM, but some might, along with horses displaying a range of sometimes vague neurological signs. When an effort is made to really establish a diagnosis, unfortunately it's not straightforward, which leads to more confusion about the disease and how to manage it.

The Animal Health Diagnostic Center at Cornell University have released a document on EPM testing and diagnosis. This document discusses when and why to test, along with important information about the available, recommended tests. It's a nice, comprehensive overview of the subject and worth a look for equine veterinarians as well as horse owners wondering whether their horse may have this enigmatic disease.

Equine Infectious Neurological Disease Update: Ontario

The latest update on equine infecious neurological diseases in Ontario (Eastern equine encephalitis (EEE), West Nile virus (WNV), rabies and neuropathic equine herpevirus type 1 (EHV-1)) is available from the Ontario Ministry of Agriculture, Food and Rural Affairs.

There aren't a lot of surprises, and it's good to see the numbers of cases have remained relatively low. Most notably, there have been three EEE and five WNV cases confirmed, from different regions of the province. This shows that these diseases are still occurring in Ontario horses, albeit at a very low rate.

You always have to consider the limitations of surveillance data like this. To make the list, a horse has to get infected, get sick enough for someone to notice, a veterinarian has to be called and proper samples have to be taken for diagnostic testing. There's certainly no guarantee that this happens in all instances, and it's reasonable to assume that a few more cases of these diseases have occurred in Ontario this year.

In Ontario, August and September tend to be the months of highest activity for EEE and WNV, and as we move into cooler weather (and decreased mosquito activity) the risk of EEE and WNV will start to plummet. I wouldn't be surprised if the numbers increase slightly by the time the final tally is made, but there are no indications that we have major disease activity at the moment.

Surveillance data such as this, including total numbers of cases in the province and an indication of areas where case occur, are important for horse owners and veterinarians to consider when determining their vaccination programs.

Equine Biosecurity Risk Calculator

After an extensive development and review process, an Equine Biosecurity Risk Calculator (click here) is now available online on the Equine Guelph website. This joint venture of Equine Guelph and Colorado State University, with support from the AAEP Foundation and Vetoquinol, is designed to offer practical advice on equine infectious disease risk and control.

While no one can really give an exact number regarding "risk" of infectious diseases on any particular equine facility, it is possible to identify areas in need of improvement. That's what this "calculator" is designed to do. Horse owners can complete the online questionnaire and get a general assessment of risk, plus detailed information about areas of concern. The calculator is free to use and no identifying information is collected.

Every horse owner should try this and see what areas are identified that could be improved. While facilities are quite variable in their application of infection control practices, I've yet to encounter a "perfect" facility - undoubtedly everyone will get at least a few ideas to consider to help reduce the risk of infectious disease in their animals.

MRSA from foal to girl

A case report highlighted by and presented at the ASM/ESCMID MRSA conference in Washington DC last week described a horse-associated methicillin-resistant Staphylococcus aureus (MRSA) infection in Dutch girl.

The girl, a 16-year-old with a severe neuromuscular disease who was wheelchair-bound and on a ventilator, developed an infection following an insect bite. When the infection didn't respond to initial treatment, a sample was taken for culture and MRSA was identified. The girl didn't have any known risk factors for MRSA infection but had had close contact with a foal. The Friesian foal had been at a veterinary hospital prior to the girl's infection. It had a wound infection that was successfully treated with antibiotics, but no culture was taken at the time. The foal was considered a possible source of the MRSA, particularly since the strain that was recovered was ST398, which is widely found in livestock and which is regularly seen in horses in the Netherlands. After the girl's infection was identified, the foal was tested and was also found to be carrying MRSA. The girl's infection was successfully treated and the foal eliminated MRSA carriage without treatment (which is expected in horses because long-term carriage of MRSA seems to be rare to non-existent in this species).

The source of the infection could not be definitively proven, but given the fact that the horse was at a facility that regularly sees MRSA cases, that the strain involved is typically associated with livestock, and that the girl had no other livestock contact, it's a reasonable to assume it came from the foal.

We've known for a few years that MRSA is an issue in horses, and that it can be passed between horses and people - in both directions. Equine veterinarians and horse owners have abnormally high MRSA carriage rates. MRSA carriers are people who have MRSA living in or on them (most often in the nose) without any signs of infection. Most carriers never have a problem, but disease can develop in some situations. The incidence of human MRSA infections transmitted from horses is low, although it's almost certain that many horse-associated MRSA infections are not reported because the link with horses isn't made or people don't mention the horse contact. article is incorrect in stating that this is only the third case of horse-to-human MRSA infection, since we've already published two such reports, one of which included multiple cases. Regardless, it's an uncommon problem but it is probably also under-recognized. Horse owners shouldn't panic about MRSA, but they should realize that MRSA is circulating in the horse population and that by nature of their frequent and close contact with horses, they are at higher risk for MRSA carriage, and likely also infection.

More information about MRSA in horses can be found on the Worms & Germs Resources - Horses page.

(click image for source)

Safe Sex For Horses

The recent (or, I guess, not so recent, since it seems to have been lingering in the background for a while) contagious equine metritis (CEM) outbreak in the US was a good demonstration of the potential impact venereally transmitted diseases can have on the horse industry. Concerns about such things are greatest in breeds that only allow live cover, since an individual stallion may be exposed to a large number of mares every year, and with the mobile nature of the horse population, it's possible for one infected horse to disseminate an infection widely across or between countries.

While CEM is probably the highest profile venereal disease in horses, it's not the only one. Other pathogens like equine arteritis virus and equine herpesvirus type-3 (equine coital exanthema virus) are also of concern, along with various opportunistic bacteria.

Proper management and infection control practices can greatly reduce, but not eliminate, the risk of sexually transmitted infections in horses. Unfortunately, such practices aren't always used. Sometimes it's because of lack of consideration or laziness. Sometimes it's because of lack of awareness. To help improve awareness and make it easier for people to take appropriate precautions, the American Association of Equine Practitioners (AAEP) has recently released Biosecurity Guidelines for Control of Venereally Transmitted Diseases. It's an excellent resource for veterinarians and horse owners, and should be part of the infection control program for anyone breeding horses.

Economic Impact Of Aussie Horse Flu

A huge equine influenza virus outbreak occurred in Australia in 2007 - a classic example of what can happen when a virus gets into an area where it's never been before. There were huge numbers of affected horses and a massive disruption to the industry due to quarantines and other control measures.

A special edition of the Australian Veterinary Journal (July 2011) includes a series of papers covering different aspects of this outbreak. In one paper (Smyth et al) the authors look at the economic consequences and tried to determine the financial costs of the outbreak. Such estimates are always tough to make and can never be 100% accurate, but they can give a general idea of the scope and impact of an outbreak. Not surprisingly, the costs were pretty astounding.

Australian Government

A series of measures were implemented to assist individuals and organization that were impacted. The total cost of those packages was over $263 million AusD.

State/Territory Governments

New South Wales and Queensland were most seriously affected, but all states and territories were impacted. These governments provided support in addition to the federal funds. For example, Queensland allocated over $27 million to various efforts, while New South Wales contributed more than $46 million.

Racing and Wagering Western Australia

This is the government body that regulates racing in Western Australia. The outbreak cost this agency around $500 000, a figure that does not include lost employee time and approximately $15 million in lost wagering revenue. Some of this was recovered through insurance, but it's now unlikely that they will be able to get further insurance to cover outbreaks.

Harness Racing Industry

It's always hard to figure out the true costs to an industry after a major disaster because the trickle down effect goes so far, affecting people who provide support and services (e.g. hay suppliers) to various businesses that are affected directly because people in those groups don't have money to spend. The total identifiable costs were calculated to be over $23 million, about half of which was to owners and trainers. The authors acknowledge the true costs were probably much higher.


A large inquiry was commissioned after the outbreak. This cost over $5 million.

Animal Health Australia

This group coordinated the emergency response and had to divert tremendous personnel time and resources. This included the vaccination program that distributed 670 000 doses of vaccine.

Households and businesses

Overall, it was estimated that horse associations lost $281 million, horse businesses $65 million and households $34 million.

Horse deaths

The value of horses that were reported to have died was close to $1 million, despite the fact that equine flu is uncommonly fatal. This number doesn't include intangible costs associated with losing a horse. However, reported deaths may be a minority and it was estimated that true horse death costs may have been $44 million. (However, I suspect the death rate estimate used for this value is high.)

Veterinary treatment

Estimated costs...$35.7 million.

Do the exact numbers matter? No. They simply show that an infectious disease outbreak can cost a lot. In many areas, horses receive little government attention because they are not food animals, despite the fact that the highly mobile horse population is probably at much higher risk of importing a new disease, and despite the fact that the economic impact of the industry is huge (and often overlooked by governments and groups that fund agricultural research).

If nothing else, this should serve as a reminder to government and industry groups that attention needs to be paid to infection control and emergency planning. While groups are often reluctant to put  much or any time, effort and funds into these areas, the amount of money that would be spent is inconsequential compared to the potential impact of even a small outbreak.

Image source:

Ontario Equine Influenza Activity

Like human influenza, equine influenza can be a seasonal disease with periods of particularly high activity. It's possible that we are in a period of high flu activity in horses in Ontario, based on cases we've seen and anecdotal information from the general population. We've seen a couple of confirmed cases of influenza over the past week (which is rather unusual), and unconfirmed rumours suggest that there may be many influenza cases in horses in the province, particularly at racetracks. Given the non-reportable nature of influenza, the often tight-lipped nature of horse owners when it comes to disease, and the typical lack of diagnostic testing to confirm flu in horses with flu-like disease, it's hard to say what's really happening.

Regardless, people should be on the lookout for influenza. Horses that develop a fever and/or signs of respiratory disease should be evaluated and isolated unless a non-infectious cause is identified. Facilities with affected horses should implement effective infection control practices to reduce the spread both on the farm and to other farms. People should discuss the risk of influenza exposure in their horses and talk to their veterinarian about whether influenza vaccination is indicated. Veterinarians can also use this situation as a reminder to owners of the ever-present risk of various infectious diseases, and as a lead-in to an assessment of the regular farm infection control plan (and if the farm doesn't have one, get started on it).

MRSA In Aussie Horses

In the early 2000s, we took a lot of bad publicity in Ontario (particularly at the Ontario Veterinary College) because of MRSA in horses. While MRSA had been found in horses before and there were anecdotal reports of MRSA infections and outbreaks in different areas, the fact that we intensively investigated the issue and published a lot of our findings made it look like we were the hotbed of MRSA internationally. We suspected at the time that MRSA was widespread in horses and that the limited reports were because few people were looking or publishing their observations. That suspicion has been supported by reports over the past few years of MRSA in horses in many countries, and it appears that MRSA is present in horses around the world.

A recent study from Australia (Axon et al, Australian Veterinary Journal 2011) provides more support for this conclusion. In the study, horses that were admitted to a veterinary hospital's intensive care unit over a 30 day period in 2008 were tested for MRSA carriage by culturing swabs from their noses. MRSA was isolated from 3.7% of horses, which is similar to the prevalence here based on data we've gathered over the years.

For the second part of the study, the authors looked at medical records from horses at the hospital from 2004-2009 and collected data on MRSA infections. During that time, MRSA was isolated from 75 horses.

  • That number (75) surprises me a little, since it's much higher than what we see here. Even though we see approximately 2% of horses carrying MRSA when they arrive at the hospital, we have a very low MRSA infection rate in our patient population. A few of those 75 horses probably didn't really have MRSA infections, since nine horses only had positive nasal samples which is more likely to be from subclinical colonization rather than infection of the nasal passages. A few others had MRSA isolated from catheter sites, and it's hard to say whether those are truly infection or just contamination of the skin. So, the number of true infections might be lower, but it's still a significant issue. It would be interesting to know how many of those horses came in with MRSA infections versus how many picked up MRSA in hospital.

Wound infections were most common, accounting for 43 (57%) of the cases. Five horses were euthanized because of the MRSA infection, all of which had joint infections that did not respond to intensive treatment.

One farm accounted for 18 MRSA-positive results in the second part of the study, as well as two positive horses in the surveillance part of the study. This farm would seem to have a pretty big MRSA problem, which we've seen occasionally on a few biohazardous breeding farms that we've found over the years.  MRSA can be controlled on farms like that but it takes effort. We've had some farms address the issue properly and eliminate MRSA, while others essentially ignored the problem and continued to have widespread MRSA for years. 

Not surprisingly, most of the MRSA isolates in the Australian study belonged to sequence type 8 (ST8), the group of MRSA that we find in horses here in Ontario and internationally. This is a recognized human strain that seems to have become adapted to horses. It's also found in a disproportionately high percentage of horse owners and horse vets, likely indicating movement of teh strain between horses and people.

Overall, the results of this study are not surprising, but are very useful in that they support the notion that MRSA is present in horses around the world, and the situation with MRSA in horses is probably quite similar in many different countries. 

More information about MRSA in horses can be found in on the Worms & Germs Resources - Horses  page.

More Mosquito-Borne Mayhem

The mosquito-borne diseases eastern equine encephalitis (EEE) and West Nile (WNV) continue to rear their ugly heads in the northeast as we get further into the late summer season during which they are most common.

On August 13 there was an unconfirmed report of a case of West Nile in a horse at Woodbine Racetrack, just north of Toronto.  No additional details have been forthcoming regarding the severity of the infection or the status of the horse, if WNV infection has in fact been diagnosed.  Nonetheless, the Ontario HBPA is urging horse owners to ensure the vaccination status of their animals for West Nile is up-to-date.  Unfortunately, if horses are not already vaccinated at this point, even vaccinating them immediately may still leave them susceptible to virus for the next few weeks until they are able to fully respond to the vaccine.  This news follows close on the heels of news reports regarding increased numbers of WNV-positive mosquito pools in various regions north of Toronto, and thus is not altogether surprising.

The first case of West Nile in a human in New Jersey was recently diagnosed in a man from Mercer County.  Again, no additional details about the severity of the infection or the man's condition are available, but the public is once again being urged to protect themselves against mosquitoes by wearing long sleeves and pants, using insect repellant, and eliminating standing water in which mosquitoes may breed on their property.  Elsewhere the death on August 14 of a four-year-old girl in New York from infection with EEE has been reported.  She is the fifth person in New York state to die from the disease in 40 years.  The girl first began showing signs of infection earlier this month, but the diagnosis of EEE infection was only reached last week.  EEE has a high mortality rate in humans as well as horses.  Just as infection in animals can act as sentinel indicators for disease risk in humans, these human cases indicate that WNV and EEE are active in these respective areas, and humans and horses alike are at risk of infection.  Mosquito avoidance can help protect both, and in addition timely vaccination of horses can help decrease the risk of disease.

West Nile Warnings

Following on the heels of the beginning of the start eastern equine encephalitis (EEE) season, warnings are going out about another mosquito-borne disease in parts of North America, West Nile virus (WNV) encephalitis. While mosquitoes have been swarming around here for months, WNV only becomes a real concern in southwestern Ontario starting in mid-to-late August. This time of year, the virus starts increasing in the mosquito population, and the types of mosquitoes that bite both birds and mammals (and therefore act as a bridge between the bird reservoirs and susceptible mammals like horses and people) become more common and more active.

Reminders about WNV have been issued in Ontario over the past few days because of increasing numbers of mosquito pools testing positive for the virus. Mosquito pools are groups of mosquitoes that are caught and tested together to see if the virus is present. The more pools that are positive, the more mosquitoes that are positive and the greater the WNV activity in the area.

People are being reminded to take measures to reduce mosquito breeding grounds on their property, which mainly means getting rid of standing water. Avoiding mosquito bites through basic measures, such as staying away from mosquito-infested areas (particularly at dawn and dusk), wearing light coloured clothing with long sleeves and long pants, using insect repellent containing DEET and making sure windows have intact screens, is also emphasized.

Recommendations are similar for horse owners; reduce mosquito breeding sites and reduce mosquito exposure of your horses (although this can be easier said than done). Vaccinating horses against WNV should also be considered. The dramatic decline of WNV infection in both people and horses after it first emerged back in 2001/2002 was quite impressive, and WNV hasn't ended up being the major problem it could have been. In 2011, there was only 1 confirmed case in a horse in Ontario. Presumably, there were more undiagnosed cases but this shows how the disease has leveled off to be an uncommon but still present issue.

Despite disease due to WNV being rare in Ontario (remember that the virus itself is not rare because the mosquito pools are still testing positive), WNV shouldn't be ignored because it still has the potential to cause severe illness in horses and people. When deciding whether or not to vaccinate your horse, consider carefully the risk of mosquito exposure, WNV activity in your local area, WNV history in horses and people in the area and your own level of risk aversion.

Bat cull for Hendra virus prevention?

As Australia faces a particularly bad year for Hendra virus, with possible expansion of the range of this serious disease, there have been calls for a mass cull of flying foxes (fruit bats).  These bats are the reservoir of the virus but also a protected species. The virus lives in the bats and is spread mainly through their urine. Horses that are exposed to bat urine or feces (e.g. grazing under a tree where bats are roosting) can become infected and then serve as a source of human infection. Being a highly fatal disease for which there is no available vaccine, looking at ways to reduce exposure to the virus is critical.  When you have a wildlife-associated disease, questions about trying to eliminate the wildlife source often arise.  Any discussion of culling wildlife leads to intense debate, and this situation is no different. Some people support culling bats in areas around people and horses, while others are opposed on various grounds, including a lack of evidence that it will be effective.

Can fruit bat numbers really be decreased? A lot of bats would have to be killed to have a significant impact on the population. Bats can reproduce quickly and migrate readily, therefore a single cull may have only a limited and short-term effect. A good understanding of the dynamics of the bat population is required to determine how many would need to be killed in a given area to have any significant impact. As Biosecurity Queensland's chief veterinarian RIck Symons stated "Culling is against government policy. I believe in terms of biosecurity it's counterproductive, because it does stress flying foxes and they're more likely to excrete (the virus). It could be filled by another bat colony the next day and if you're moving them on, you're moving it on to somebody else and it's somebody else's problem, so that is not the solution."

Will a cull actually achieve anything? Even if effective at reducing bat numbers (probably just in the short term), culls don't necessarily have an impact on disease rates. All bats would not be eliminated, and it's unclear whether there is a critical mass of bats that is required to transmit infection or whether a small number of bats distributed across the same region would be as likely to result in infections. Small or temporary decreases in bat numbers may have no effect.

What unintended consequences might occur if a cull is effective at reducing bat numbers? Removing an animal from any ecosystem has an effect, and it's important to be confident that that effect isn't accompanied by problems of its own. I don't know enough about fruit bat ecology to say much here, but if this species is greatly reduced, are there other species that will come and occupy that ecological niche, and might they be associated with problems of their own? Careful scientific study can help to figure this out in theory, but you can never be certain.

Are other control measures, such as removing roosting sites from pastures and other bat avoidance measures, being adequately used? Culls should only be considered when other measures have failed, but it can be difficult to ensure or enforce compliance with these other measures. Certainly, people in endemic areas should remove trees in which bats roost from pastures. However, not all Hendra cases are associated with identifiable roosting sites.  For example, one affected Queensland farm does not have any fruit bats residing on the property, but it lies along a common flight path for the bats.

It's easy to talk about avoiding a cull when you're not in the heart of the Hendra epidemic, and I understand the reasoning behind the calls for a cull. Hendra is a devastating disease that's a threat to both horse and human health, and it's unpredictable - and that's scarey for a lot of folks. People that have been exposed face an incredibly stressful period while they wait and see if they've been infected with a virus that kills in ~50% of cases. A vaccine is probably still a couple of years away, leaving a period of continued risk and stress. With such a serious disease, considering culling is reasonable. However, it can't be a knee-jerk reaction to public outcry. It needs to be based on sound science to ensure that if it's used, it will be effective. The impact on this protected species also can't be ignored.

This Worms & Germs blog entry was originally posted on equIDblog on 19-Jul-11.

Animal first aid kit recall

Earlier this year, there was a large recall of pre-packaged alcohol wipes made by Triad Group because of bacterial contamination and implication of the wipes in a large number of human infections. While alcohol is used as an antiseptic, bacterial spores are inherently resistant to the effects of alcohol and contamination with spore-forming bacteria can turn wipes into disease vectors. In the latest outbreak, alcohol wipes were contaminated with Bacillus cereus and implicated in the deaths of 7 people.

As an extension of the earlier recall, Creative Pet Products and MAI/Genesis (Veterinary Concepts) have recalled first aid kits marketed for use in pets and horses. In addition to the potential for contaminated alcohol wipes there is concern that the "sterile" lubricant jelly may not be so sterile, and could also be contaminated with Bacillus cereus. Additionally there is mention that the iodine pads could be contaminated with another bacterium, Elizabethkingia meningoseptica. (It sounds like they have some pretty major quality control issues. Not surprisingly, production at the plant has been suspended pending an ongoing FDA investigation.)

Anyway, anyone with one of these first aid kits should check to see if their kit is involved in the recall:

Alcohol prep pads – Kits affected:
10140 Horse Aid™ Kit
10145 Sporting Dog Kit
10148 Sporting Dog II Kit
10151 K9 First Aid Police & Military Kit
Brands: Triad or NovaPlus
All Lot Numbers

Iodine prep pads – Kits affected:
10140 Horse Aid™ Kit
10145 Sporting Dog Kit
10148 Sporting Dog II Kit
Brands: Triad or H&P Industries
Lot Numbers starting with 8, 9, 0, 1

The kits were distributed in the United States, Australia, the United Kingdom, Taiwan and Costa Rica.

If you have one of these kits, you should get rid of the affected items. For further details (and presumably how to get a refund) click here.

This Worms & Germs blog entry was originally posted on equIDblog on 09-May-11.

More on vets and MRSA

There are a number of published studies regarding methicillin-resistant Staphylococcus aureus (MRSA) carriage by veterinarians, most reporting high rates compared to the general population. This is a concern because MRSA is an important cause of disease in both people and animals. Just having MRSA living in your nose doesn't mean you're going to get sick. Indeed, around 2-3% of normal, healthy people are likely carrying MRSA at this moment. However, if you are carrying MRSA, you are at increased risk of developing an infection under certain circumstances. In veterinarians MRSA carriage is also a concern because of the potential for transmission to patients (and potentially from those patients back to people).

A recent Australian study in the Australian Veterinary Journal (Jordan et al 2011) looked at MRSA carriage in different types of veterinarians. The rates were:

  • 0.9% in industry and government veterinarians (who have limited contact with animals)
  • 4.9% in small animals veterinarians
  • 11.8% in veterinarians with horses as a major component of their caseload
  • 21.5% in equine veterinarians

These results are similar to some of our earlier studies, with carriage rates in small animal veterinarians being  higher than would be expected for the general population, and carriage rates in equine veterinarians being very high.

Why do veterinarians have high rates of MRSA carriage?

There's no definitive answer but there are some likely causes. Veterinarians have contact with large numbers of pets and horses, and we know these animals can carry MRSA. Even if the percentage of dogs, cats or horses carrying MRSA is very low, when you multiply that by the number of animals a veterinarian touches every week, you can see how contact with an MRSA-carrier is pretty likely. Veterinarians also tend to have close contact with sites where MRSA can be found, such as the nose. This makes the chance of having contact with the bacterium itself more likely. An additional issue the often sub-optimal use of routine infection control and hygiene practices (especially hand hygiene), which may also increase the risk of MRSA transmission. Put all these together, and it makes sense that veterinary personnel are at increased risk.

Why do carriage rates tend to be higher in equine veterinarians?

It could be because MRSA is more common in horses than small companion animals. Another plausible explanation is the fact that the horse's nose (the most likely site for MRSA to be living) is commonly touched during examination and restraint, and horses have pretty big noses to start. Additionally, good hygiene can take more effort on some farms, as sinks and often even hand sanitizer are not as readily available as they are in a clinic.

More information about MRSA in companion animals can be found on the Worms & Germs Resources page.  More information about MRSA in horses can be found on our sister site, on the equIDblog Resources page.

(click image for source)

This Worms & Germs blog entry was originally posted on equIDblog on 19-Apr-11.

Murray Valley encephalitis suspected in Aussie man and horses

Yesterday, I wrote an equIDblog post about an outbreak of unexplained neurological disease in horses in the Murray River region of Australia.  Today, a ProMed report indicates that Murray Valley encephalitis is now being considered as a possible cause of death in a man from the area.

Murray Valley encephalitis (MVE) is one of the possible causes of the equine neurological disease outbreak, and it's quite likely that if it caused disease in one species in the region, it did the same to another. This rare mosquito-borne disease hasn't been seen in decades in the region, but it's possible that high mosquito numbers following heavy rainfall and flooding have increased the risk of transmission.

While this virus poses a risk to both humans and horses, humans and horses pose no risk to each other.  Both acquire the disease the same way - from mosquitoes - and neither can pass it on to the other.  This is also true of other insect-borne viruses such as West Nile virus and Eastern Equine Encephalitis (EEE) virus.

This is a good example of why human and animal disease surveillance need to be linked, and why governments need to put resources into testing of animals beyond food animals. Rapidly identifying a disease in horses or other animal species can help determine whether there is any risk to humans, and hopefully lead to preventive measures being taken earlier.

Prevention of this disease is focused predominantly on mosquito avoidance. It's impossible to completely prevent mosquito exposure, but some basic practices can help reduce the risk.  Click here for some practical tips on protecting yourself and your horses from mosquitoes.

Image: Location of the Murray River in Australia (click for source)

This Worms & Germs blog entry was originally posted on equIDblog on 13-Mar-11.

2010 Animal Rabies Summary

In Canada, rabies testing and surveillance is performed by the Canadian Food Inspection Agency (CFIA). National data for 2010 are now available and indicate there were a small number of cases in domestic animals, with more in wildlife, for a total of 123 cases.

Dogs: There were three cases, all in Saskatchewan.

Cats: Four cases, three in Manitoba and one in Alberta.

Horses: One rabid horse in Manitoba.

Cattle: One, from Manitoba.

Skunks: 60 cases, 33 in Manitoba, 17 in Saskatchewan and 10 in Ontario.

Bats: 48 rabid bats, most in Ontario (29) but also in BC, Alberta, Saskatchewan, Manitoba, Quebec, New Brunswick and Nova Scotia.

Foxes: Six from the Northwest Territories or Nunavut.

No rabid sheep, goats, raccoons (down from 58 in 2007), wolves or other species.

Manitoba seems to win the 2010 rabies prize, while Newfoundland and Labrador, Prince Edward Island and the Yukon had no cases.

As with any disease surveillance, these numbers underestimate the scope of rabies. For an animal to appear on the list, rabies had to be considered and testing performed. So, for  wildlife, it's a massive underestimation of the number of cases, since most affected wildlife don't get tested. Wildlife testing (and testing in general) is typically only done when there has been the potential for human exposure. Domestic animal cases are probably a fairly close representation of the status of rabies in pet and farm animals, since it's reasonably likely that a domestic animal with rabies would be identified as such and tested (although certainly cases can be missed or neglected). As with wildlife, there is probably an under-identification of rabies in feral/stray dogs and cats, since testing would only be done on these animals if they are caught and if there was potential human exposure.

Lions and tigers and glanders

Glanders, a very serious disease of horses, donkeys and mules caused by infection with the bacterium Burkholderia mallei, has made the news again in a rather unusual manner – it has been reported as the cause of an outbreak in lions and a tiger at an Iranian zoo in Tehran.

The story goes that two Amur tigers arrived at the Tehran zoo from Eastern Russia in April 2010 as part of an exchange program between the two countries. The tigers were supposed to be used to help restore the tiger population in northern Iran on the Miankaleh nature reserve, but their living quarters there were apparently still not ready, and thus they were being kept at the zoo. One of the tigers died in December 2010.

And that’s were the story starts to get a little dicey. The Iranians claim the tigers were imported already carrying the disease, and that the last case of glanders at the zoo was 50 years ago. The tigers had already been at the zoo for eight months - although the incubation period for glanders can be months in some cases, it is normally only weeks. The Russians of course insist that the tigers were completely healthy when they were transferred – they’d been thoroughly examined and quarantined prior to being moved. (This makes the most sense to me, since transporting an animal such a long distance is a major stress and increases the risk of illness, and transporting an animal that is already sick would be even more risky. Not a chance I would take with two members of a species of which there are fewer than 900 individuals left in the world.) They also pointed out that a sick tiger from the cold regions of Russia would be much more likely to succumb to illness during the very hot Iranian summer, not during the winter.

Another report said that three lions at the zoo also died from glanders in the last two months, and subsequently another 14 lions were diagnosed with the disease, all of which were put down by the authorities. The main concern seemed to be the spread of the disease from the big cats to the feral cat population, and then to the human population. This second report states that “the tiger died after being fed contaminated meat, though it is possible it could also be related to the glanders.”  Yet another report said that the tiger was infected with feline immunodeficiency virus (FIV - the feline equivalent of HIV).

Facts to keep in mind:

  • Glanders is an highly contagious disease, and highly fatal (B. mallei is even classified as a Class B bioterrorism agent).
  • Animals that do recover from the disease can become long-term carriers of B. mallei, and are a risk to other animals (and people). Prompt euthanasia of affected animals is therefore often the primary means of controlling outbreaks (but the bacterium is susceptible to antibiotics).
  • The infection can be transmitted to other animals (and people), usually through close direct contact or contact with oral and nasal secretions and discharge from skin ulcers. It can also be transmitted by eating tissues from infected animals.
  • The bacterium is killed by most disinfectants, and UV radiation (sunlight).

Glanders can affect species other than equids, including people and cats, however there is very little information available about glanders in any felids, let alone lions and tigers. Theoretically it might be possible for the disease to spread from the zoo animals to feral cats and then to people, but I don’t know how many feral cats are brave (or stupid) enough to wander into a lion enclosure. There’s also a possibility that a glanders-positive feral cat may have infected the zoo cats (but again, it would have to be very brave, or very stupid). It is also unclear what tests were used to confirm that the big cats were infected with glanders, and it is unknown if other animals at the zoo have been tested. Since this is typically a disease of equids (and has also been found in goats and camels), I would certainly be checking these animals first.

The big question is, where did the glanders come from in the first place? It seems unlikely that the tigers brought it from Russia, when the disease is actually endemic in Iran (even though they’d had no diagnosed cases at the zoo for many years). Is there a carrier animal in the zoo? Were the animals infected by eating contaminated meat? Was it brought in by feral cats?  The source needs to be identified and addressed or animals will continue to be infected, which is particularly bad news for the kinds of rare species that may be found in a zoological collection. Some more details about the testing would also be appreciated – given the severity of this disease, and the severity of the consequences for positive animals (euthanasia), one needs to be as sure as possible that these animals are infected with B. mallei and not something else.

Photo: Amur Tiger (Panthera tigris ssp. altaica) (click image for source)

Probiotic safety

The November edition of Emerging Infectious Diseases contains a commentary about probiotic safety. The paper, entitled "Regulatory Oversight and Safety of Probiotic Use" (Venugopalan et al. 2010), focuses on a probiotic yeast, Saccharomyces boulardii, which is increasingly being used for treatment or prevention of Clostridium difficile infection in people. Because it is marketed as a dietary supplement, this yeast doesn't have the same requirements for demonstration of safety and effectiveness as a "drug" would. Systemic Saccharomyces infections have been reported, predominantly in people who are critically ill or who have other risk factors for an infection caused by a microorganism that is typically harmless.

The lack of regulatory oversight limits the identification and reporting of problems associated with probiotic administration, and means that safety testing is not required, even if the product will be used by high risk individuals. Often people consider probiotics completely innocuous, and they don't think about the potential for complications. While very low, the risk of infection caused by the probiotic organism itself needs to be considered, especially when dealing with high risk patients and situations for which there is little proof that probiotics might be effective. 

Are probiotics safe for use in animals such as pets and horses? Probably.  For the vast majority of animals, the majority of probiotics are likely safe. Given the very lax nature of licensing and poor reporting of complications, it's hard to be definitive, but the likelihood of a significant problem occurring from giving an animal a probiotic is pretty limited. The fact that most commercial products actually contain few live organisms, a fraction of what is claimed on the label, probably increases safety (while also decreasing the chance that they work).

My general line is that probiotics are unlikely to do any harm for your average healthy animal. I have no problem with people trying probiotics in those cases, with the understanding that we really have little evidence that they work, but that they might. I am hesitant to use them (or recommend them) in very young animals, very old animals and animals with compromised immune systems. These types of animals are at increased risk of infection by even rather innocuous organisms that would not likely cause disease in other animals. Since the evidence that probiotics might work is lacking, I'm more careful when dealing with such high-risk groups. What we really need is sound research to provide the required evidence of probiotic safety and effectiveness.

Image: Coloured scanning electron micrograph of Saccharomyces boulardii (source:

Horse bite leads to meningitis

You never want to be the subject of a medical case report. A 37-year-old British woman was featured in a recent edition of Lancet (Brouwer et al 2010), in a paper entitled "A horse bite to remember."

The woman was admitted to hospital with a fever, headache, neck stiffness, confusion, difficulty speaking and nausea. These signs are suggestive of meningitis and a spinal tap was supportive of that presumptive diagnosis. Blood samples were also taken, and the same bacterium, Streptococcus zooepidemicus, was isolated from both blood and spinal fluid, confirming a diagnosis of S. zooepidemicus meningitis. She was treated and improved, but did not fully recover.

Streptococcus zooepidemicus is primarily associated with horses, although it can occasionally be found in other species such as dogs. After the diagnosis, the woman's family was questioned about her hobbies and it was revealed that she was an avid horsewoman. Further, she had been bitten by her horse the previous week. That was the presumed source of infection, but it doesn't appear that any further investigation was undertaken.

Associating the meningitis with the bite is reasonable, but it's not definitive. Streptococcus zooepidemicus infections in people have occurred in the absence of bites or other clear sources of exposure to horses, so the bite wasn't necessarily the problem. Regardless, it indicates the need to be proactive and properly treat any horse-associated wound, be it a bite or any another wound that gets contaminated with bacteria from the horse or its environment.

This was a very unusual case. People shouldn't be overly concerned about getting S. zooepidemicus meningitis from their horse. However, it should serve as a reminder that bad things can happen periodically and that proper attention to general hygiene practices and bite wound care is always important.

On a side-note, I thought the title "A horse bite to remember" was a bit crass, since the woman is now unable to live independently because of severe amnesia (memory problems) as a result of the infection. Maybe they were trying to be ironic, but it seems below a journal such as Lancet.

This Worms & Germs blog entry was originally posted on equIDblog on 10-Oct-10.

Vaccine reactions: Real and imagined.

The other night, my daughter woke up yelling that she was "scratchy." She was quite upset and it continued for a while, despite my best attempts to calm her down. She had a bit of a fever and shortly after broke out in a good case of hives all over her body.

How is this relevant to this blog? Well, earlier that day, she was at the doctor's for her 3-year checkup. She wasn't vaccinated, but Heather made the observation that had she been vaccinated at that appointment, we would have wondered whether this was a vaccine reaction.

Determining whether something is a vaccine reaction can be tough. Too often, people blame a wide range of abnormalities on vaccination, without realizing that they occur at other times too.

The post I wrote a couple of days ago about rabies vaccination mentioned people not vaccinating their horses because of fear of vaccine reactions. I think it's fair to say that there are many more people that think their horse has a problem with vaccines than there are horses that truly have vaccine reactions. Sometimes, people are looking for an excuse not to vaccinate. Often, however, they are really convinced that a vaccine reaction occurred, even though the evidence may be weak.

A good example of this is West Nile virus vaccination. When West Nile virus vaccine first became available, there were rumours that it caused stillborn and deformed foals. There were internet sites reporting cases and publishing pictures of aborted fetuses. However, just because a mare was vaccinated and later aborts, that does not mean that the vaccine caused the problem. Lots of mares that aren't vaccinated have problems. That's why we do research - to see if problems like that are more common in vaccinated horses versus unvaccinated horses. Despite the internet paranoia, there is no evidence that West Nile virus vaccination produces dead or deformed foals, and fortunately this rumour seems to have died down. (I have to wonder how many horses died from West Nile because they weren't vaccinated as a result of this rumour. When some people stopped vaccinating children for measles because of false concerns about autism, there were tremendous increases in measles cases in many areas.)

Vaccine reactions can and do happen. There's no disputing that. Most are mild but some can be severe. However, lots of animals can develop identical-looking of problems at any given time. Just because they were vaccinated recently does not mean that the vaccine caused the problem. A vaccine reaction should be considered when abnormalities develop around the time of vaccination, but automatically blaming the vaccine must be avoided.

Some things to consider:

  • Has the horse had this specific vaccine before? A reaction is probably less likely if the horse has had this specific vaccine multiple times in the past with no problems.
  • Is the problem something that is typically observed with a vaccine reaction? Development of hives after vaccination is pretty suggestive, although it's not definitive. Other problems may be hard to link to vaccination.
  • Was a single or combination vaccine used, or were multiple vaccines given at the same time? If a combination vaccine was used and the potential reaction wasn't severe, giving the specific components of the vaccine individually next time might help determine if it is a vaccine reaction and which component caused the reaction. There's no use stopping all vaccinations if the horse might only be reacting to one specific component. Sometimes, avoiding combinations is all that is needed (although whether that's because it decreases the risk of reactions or whether there wasn't actually a vaccine reaction in the first place is debatable). If there is a problem with one component, then that single component can potentially be skipped but the other vaccines still given.
  • Was it a severe reaction? If not, then not having the vaccine may be a bigger risk than vaccinating. It depends on the disease and the risk of exposure. Also, pre-treatment of the horse with an anti-inflammatory may be enough to prevent a mild reaction or decrease the severity of a more significant reaction.
  • Are there some horses that have severe reactions and can't be vaccinated safely? Yes, but there are very few. Vaccination decisions need to take into account the cost-benefit, in terms of protection and adverse effects. Sometimes, the risks are greater with vaccination, but usually they are not. If you think your horse has a problem with vaccines, work with your veterinarian to determine the best approach. Don't let a knee-jerk reaction automatically prevent you from vaccinating.

Image: A horse with hives along its neck (click image for source)

This Worms & Germs blog entry was originally posted on equIDblog on 16-Sep-10.

Equine rabies vaccination poll's latest reader poll asked the question "If you knew rabies had been found in wildlife in your area, would you vaccinate your horse for it?"

  • 79% of respondents said they already vaccinate against rabies annually.
  • 16.5% said they don't currently vaccinate but would if it was found in wildlife in the area.
  • 4% still wouldn't vaccinate.

The high vaccination rate is very encouraging and is a good sign, considering that rabies, while rare, is 100% fatal in horses and is preventable with early vaccination.

Here are some reader comments (with some additional commentary from me):

Develop a strong immune system instead try to avoid all the drugs

  • Keeping your horse healthy is a good disease prevention measure, but it is not good enough for prevention of rabies. This is a foolish approach to rabies prevention.

Used to yrly. vaccinate in MI, but vets here in KY don't recommend it/My Vet keeps telling me it is not necessary, same with my daughter horses. I disagree.

  • This, and a few other comments about veterinarians not recommending vaccination is very surprising and concerning. Rabies vaccination is considered a "core" vaccine in North America and it makes no sense for veterinarians to be actively discouraging vaccination.

Too many adverse reactions...bad outbreak, might reconsider/There have been too many adverse reactions to the vaccine, I won't take the risk of vaccinating.

  • Adverse reactions can occur with any vaccine, but they are quite rare with rabies vaccine. Sometimes, horses react when they are given a variety of vaccines at the same time, and it might not be rabies vaccine with that caused the problem. Often, the risk of adverse reactions is just used as an excuse not to vaccinate, even if the horse has never had a problem. 

Vaccination is necessary when horses are turned out nearly 24/7

  • Yes. It's also necessary when horses are inside 24/7. Wildlife (especially bats) easily and often get into barns.

I don't vaccinate yearly because I test titers and they remain high for many years.

  • Titre testing is not useful because we don't know what a protective titre is. You can take a titre and get a result, but that doesn't mean the horse is protected. Also, if your horse is exposed, it would be considered unvaccinated by government officials if it had not been recently vaccinated, regardless of titres.

I would be especially diligent to vaccinate if aware of a wildlife outbreak of rabies/I have only vaccinated when there have been cases of rabies, otherwise, I don't.

  • I have a couple of problems with this type of approach. Firstly, you only recognize an outbreak AFTER a large number of animals get sick. Waiting until someone reports an outbreak doesn't help you if your horses are among the first ones affected. Also, rabies isn't a disease that mainly occurs in outbreaks. It is a sporadic disease, where single cases or small numbers of cases pop up all the time. Only worrying about it during an outbreak doesn't help.

I would vaccinate my dogs and cats, but not my horse.

  • Why? If there is a risk of the dogs and cats being exposed, there's a risk of the horse being exposed. (Maybe they like their dogs and cats more!)

I can't buy rabies vaccine only vets can get it so I don't give rabies shots.

  • So, if I can't do it myself (translation, if I can't do it very cheaply), I won't do it. Not a good infection control program.

NEED ANOTHER CHOICE! I run titers. Vac. is indicated every 3-5 years

  • Nope. Vaccination is safe and effective. Standard recommendations are for yearly vaccination. Could we extend that, as is now done with dogs and cats (in which 3 year vaccines are now widely used)? Probably, but we don't have the data to guide us. We can make some reasonable guesses, but do you really want to use a vaccination program designed to protect against a fatal disease to be based on guesses?

The chances of my horses being bit by a rabid critter are slim to none. I don't believe in vaccines

  • I don't think anyone can say that the chance of their horse encountering a rabid critter is slim to none. People encounter rabid critters inside their houses, while walking down the street and in various other situations. I certainly didn't plan on catching a rabid bat in my house, but it happened.
  • Not believing in vaccines is just ignorance. Vaccination is critical for protection against a wide range of diseases. Can adverse reactions occur? Sure, but they are very uncommon (internet rumour mills aren't facts). Do vaccines prevent infections and save lives? Undoubtedly. What happened when people started avoiding MMR vaccines in kids because of now-discredited autism concerns? Lots of people got sick.

Live in UK, no rabies here generally

  • Good reason. Rabies vaccination isn't needed in rabies-free countries.

Fortunately, there were also a lot of logical comments like:

  • I never go without this vaccination. it's way to risky!!!
  • With all the wildlife around, it's not worth risking an unintended encounter causing big problems.
  • Why would you take a chance and not vaccinate...
  • Ever since my uncle's horse died of rabies, I have vaccinated all my horses annually.
  • Are you kidding? Who'd take a chance with rabies?

And as one person so eloquently put it "DUH!"

Apart from the extremely small small number of horses with known and potentially severe reactions to rabies vaccine (not just any vaccine, specifically rabies vaccine), and those living in rabies-free countries, all horses should be vaccinated.

Image: A Little Brown Bat (Myotis lucifugus) roosting under the eaves of a house (click image for source)

This Worms & Germs blog entry was originally posted on equIDblog on 15-Sep-10.

Sequence type 398 MRSA infection from horse to human

Methicillin-resistant Staphylococcus aureus (MRSA) is a huge problem in people and is an emerging pathogen in horses. Most earlier reports of MRSA in horses involved one strain, called CMRSA-5 in Canada, USA500 in the US, and sequence type 8 (ST8) as a more general term. This human-origin strain seems to be adapted for survival in horses, and in North America, this strain has accounted for most MRSA infections in horses and MRSA infections in people linked to horse contact.

Another MRSA strain, ST398, has recently emerged as a big problem associated with livestock (particularly pigs). This strain is very common in pigs internationally, and is a major cause of infections in people in some European countries. There are also a few reports of ST398 in horses. Most are from Europe, although we have found this strain in one horse in North America. At last week's ASM Conference on Antimicrobial Resistance in Zoonotic and Foodborne Pathogens in Toronto, Dr. Engeline van Duijkeren from the Netherlands presented a case of human ST398 infection linked to a horse.

In the reported case, a 16-year-old girl had a lesion on her foot that was initial diagnosed as a spider bite infection (a common misdiagnosis of early MRSA skin infections). It didn't respond to initial treatment and MRSA was isolated on culture. The girl didn't have any history of contact with pigs or cattle, but had close contact with a foal. That foal had previously been in an equine hospital because of a wound infection, but the wound was not cultured. The same MRSA strain that caused the infection in the girl, however, was found in the foal's nose (the prime site for MRSA carriage by healthy horses). Fortunately, the girl's infection responded to treatment once treatment was adjusted for MRSA.

In some ways, this case is not too surprising, since we know ST398 MRSA can cause disease in people, and since it is found in horses, transmission from horses to people was likely inevitable. However, it's the first report of human infection with this strain associated with horse contact. MRSA exposure is a potential risk for anyone working with horses, since we know that this organism can be found in a small percentage of healthy horses. We don't have great information about how to prevent horse-human transmission, but simple things like only using antibiotics when needed and attention to hygiene (especially hand washing) when working with horses are presumably important factors.

More information about MRSA in horses can be found on the equIDblog Resources page.

This Worms & Germs blog entry was originally posted on equIDblog on 14-Jun-10.

Strep zoo infections in people

Streptococcus zooepidemicus is an important cause of infections in horses. This bacterium can also be found in healthy horses. When you consider the large number of horses that are infected and the larger number of healthy horses that are carriers, along with the close contact that people have with horses, it's pretty obvious that people are regularly exposed to "Strep zoo". This bacterium is not well-adapted to survive in people and cause infections, so human infections are quite uncommon, but they can occur. There are periodic reports of S. zooepidemicus infections in people, with varying degrees of association with horse-contact.

An upcoming edition of journal Epidemiology and Infection contains a report of S. zooepidemicus meningitis in a 51-year-old woman (Minces et al, 2010). This person had a mild upper respiratory tract infection, then developed signs of meningitis (including fever, unresponsiveness, respiratory distress). A spinal tap was performed and S. zooepidemicus was isolated. The woman fortunately responded to treatment and recovered.

Upon initial questioning of the patient's mother, no animal contact or ingestion of unpasteurized dairy products (another risk factor) was reported. However, it was later revealed that the woman's daughter had started horseback riding at a friend's farm approximately one month earlier. The type of contact that the woman had with horses (if any) at the farm was not reported, nor was there any investigation of S. zooepidemicus shedding by horses on the farm.

Based on the fact that this is typically an equine-associated bacterium and the history of contact (albeit potentially limited or indirect) with horses, horse contact was blamed for the infection. It's a reasonable conclusion but it's far from certain because of the nature of the contact, the lack of any proof of the same strain of S. zooepidemicus in horses on the farm, and previous reports of infections occurring in people with no contact with horses.

Exposure to S. zooepidemicus is an inherent risk of having contact with horses. It's nothing to lose sleep over and is probably relatively low on the list of potential health problems associated with horse contact. The risk is probably greatest in people with compromised immune systems and other general risk factors for disease such as advancing age and pregnancy. Good general hygiene measures, avoiding contact with sick horses and close attention to hand hygiene probably minimize these already low risks.

(click image for source)

This Worms & Germs blog entry was originally posted on equIDblog on 25-May-10.

Dogs also affected in 2007 Australian equine flu outbreak

In 2007, there was a massive equine influenza outbreak in Australia. A large number of horses were infected in this country that was previously equine influenza-free, and there was tremendous economic disruption caused by containment measures. It turns out horses weren't the only animals infected. A report in the April edition of Emerging Infectious Diseases describes influenza infections in dogs associated with the equine outbreak.

In some ways, it's not too surprising. Canine influenza in North America is caused by H3N8 influenza that moved from horses to dogs. Similarly, H3N8 influenza of equine origin has been identified in dogs in the UK. So, while it's an uncommon event, we know that in some situations, the "standard" equine H3N8 influenza virus can infect dogs.

The first dog that was diagnosed lived near a large horse stable. The dog developed typical signs of influenza: decreased appetite, lethargy, nasal discharge and cough. After the first dog was identified, other dogs were noted to have similar signs, including dogs whose owners had contact with infected horses and dogs that had contact with other sick dogs. Some dogs had severe infections. Influenza was diagnosed through detection of antibodies in their blood, and the influenza virus was isolated from one dog. The virus that was isolated was the same as the one present in horses (and different from that in US dogs).

For influenza to jump between species a few things have to happen.

  • First, the virus has to be able to infect the other (non-natural) species. This can happen because the virus is inherently able to infect different species or because of a random viral mutation that allows for infection of the new species.
  • Second, the virus must encounter that host (in this case, dogs). It must then be able to multiply within the new host.

All this can happen with or without development of disease. For the virus to truly establish itself in the new species and spread (like canine flu did in the US):

  • The virus must be able to multiply well in the new host, and adequate virus levels must be produced for the new host to be a source of infection to other individuals.
  • The new host must come into contact with other susceptible individuals.
  • The virus must be able to infect new hosts readily enough to maintain infection in the population, instead of dying out after a couple transmission cycles.

In these Australian cases, while it is apparent that equine flu was able to infect dogs, there was no clear evidence that perpetual dog-to-dog transmission occurred. Influenza virus was rarely detected in nasal secretions from infected dogs, making it unlikely that the virus would spread between dogs.  Therefore, the virus was not able to establish itself in the dog population. This means it ended up being only an interesting situation that affected a limited number of animals, instead of the creation of a new, self-propagating infection that could continue to circulate in dogs in the country.

(Click image for source.)

Cause of Bahraini horse outbreak identified

A recently reported outbreak affecting horses in Bahrain has been diagnosed as glanders, a very serious bacterial infection caused by the highly contagious bacterium Burkholderia mallei. So far, it has been reported that 8 horses were euthanized over the past 3 weeks because of the infection.

Bahrain's cabinet has allocated BD150 000 to fight the outbreak. Authorities have apparently stated that the outbreak can be "easily" managed, "We have sent samples from nearly 400 horses to a specialist laboratory in the UAE and the 10 results we have got so far give us the all-clear. We now know we can manage this quite easily and are taking appropriate action."

That's a pretty dangerous sentiment to be expressing (and believing) early in an outbreak, but hopefully it's true. "Easily" and "outbreak" aren't often uttered in the same sentence, and it's far from unusual to be fooled by an allegedly contained or controlled outbreak. I'd be very surprised if all of the positive horses have already been identified. Control of glanders involves widespread testing of horses, typically with euthanasia of any infected animals. It sounds like testing is underway and results of this will give a good indication of the extent of the problem. Ten negative samples don't mean that much to me. As more results come in (and if they continue to be negative), more confidence can be had in the assessment that this outbreak is truly contained.

Glanders is not solely a concern for horses. It's a zoonotic disease that can cause rare but serious infection in humans, with a high mortality rate (almost 100% if proper treatment is not administered). People can become infected by direct contact with infected horses, with the bacterium gaining entry through skin abrasions, inhalation or contact with tissues of the mouth and nose. Pneumonia, bloodstream infections and other problems can develop. Burkholderia mallei is a Class B bioterrorism agent. Hopefully, people working around infected horses are using appropriate infection control precautions to reduce the risk of infection.

Hopefully, more information will be available soon about this outbreak and results of ongoing testing.

Image: A horse with glanders (Burkholderia mallei infection), exhibiting the characteristic infectious nasal discharge.  Glanders is a reportable disease which has been eradicated from North America, Australia and most of Europe.

This Worms & Germs blog entry was originally posted on equIDblog on 26-Apr-10.

West Nile virus from pony to vet student

The latest edition of the journal Emerging Infectious Diseases contains an article about a South African vet student that acquired West Nile virus from a pony while performing a necropsy. Occupational exposure to infectious diseases is an inherent risk in veterinary medicine. Veterinarians know that they are at higher risk of encountering various infectious diseases and take (or should take) precautions to reduce those risks. Sometimes infections occur despite the best precautions. Sometimes infections occur because of bad practices. This report highlights the latter.

In this case, a 4-month-old pony began showing vague signs of illness, then developed neurological abnormalities and was euthanized. A necropsy (post-mortem exam) was then performed by a veterinary pathologist with the assistance of two veterinary students. As part of the necropsy, the student removed the brain and spinal cord for testing, but gloves were the only protective gear that were used. No face or eye protection was used, which is quite astounding.

The pony was eventually diagnosed with West Nile virus. Six days after performing the necropsy, the veterinary student developed a fever, malaise, sore muscles, stiff neck and severe headache. West Nile virus infection in the student was confirmed, and the viruses from the pony and person were the same type based on testing. Fortunately, the signs of infection in the student subsided after approximately ten days.

Horses are considered "dead-end" hosts for West Nile virus, meaning they cannot naturally transmit the virus. This is because horses (even severely affected ones) only have very low levels of virus in their blood, so a biting mosquito can't pick up the virus and transmit it to other individuals. However, the brain and spinal cord, particularly in a clinically affected horse, may contain very large amounts of the virus. It's astounding that a veterinary school would have a student removing the brain and spinal cord of an animal that died from a neurological condition, especially without proper protective gear, since the procedure carries a risk of splashing or aerosol exposure to the virus. Anyone performing necropsies needs to be aware of the potential risks and take appropriate precautions. The paper states that after the incident, biosafety practices were improved to include the wearing of masks and eye protection during necropsies. Well, I guess it's better late than never...

Click image for source.

This Worms & Germs entry was originally posted on our sister site, equIDblog, on 11-Mar-10.

2008 Australian Hendra virus recap

The latest edition of the journal Emerging Infectious Diseases contains a paper describing the 2008  Australian Hendra virus outbreak in horses and people.

In this outbreak, there were five horses infected and two humans infected. The horses predominantly had signs of neurological disease, not respiratory disease like some other reports describing this disease. Four horses died. One recovered but was euthanized for public health reasons.

Two people became infected after working with the sick horses, which represents 10% of the total veterinary staff that were exposed to the infected horses.  Both people started off with influenza-like illness, which seemed to improve initially, but then signs of severe neurological disease developed. They were treated with ribavirin, an antiviral drug, as part of an experimental treatment. One of them died after 40 days of illness, the other person survived.

The authors stressed that the effectiveness of ribavirin could not be determined, but they recommend it nonetheless because of the severity of Hendra virus infection and lack of other options. Ribavirin was also used in the 2009 outbreak, but it is clearly not 100% effective since one person died there also.

A number of concerning activities occurred that put people at risk of infection, including a "percutaneous blood exposure while euthanizing an infected horses" (they didn't explain exactly what this was, but it could have been a needlestick), low use of personal protective equipment, and contact with potentially infectious body fluids. This is unfortunately not surprising since the approach to infection control (particularly in terms of zoonotic infections) is often lax in equine medicine. That certainly has to change, particularly in areas where Hendra virus may be present.

Much more information about how to control this potentially devastating virus is needed. Fortunately, infections are uncommon and it is restricted to a fairly small geographic range in Queensland, Australia.

Image source:

This Worms & Germs blog entry was originally posted on equIDblog on 27-Jan-10.

Bare feet and horse bugs

I assume that people wouldn't voluntarily and regularly walk around barefoot on dog feces (or feces of any type), yet it's perplexing that some people regularly clean out horse stalls in bare feet (I've seen it done!). While horse manure may not be as inherently gross as dog poop, it's still feces, and like all feces contains a huge population of various bacteria, some of which can be harmful. The risks of barefoot mucking may also extend to bare feet inside boots, although I don't think sock-averse people need to panic.

An article in the International Journal of Infectious Diseases (Friederichs et al) describes infectious arthritis of the shoulder of a horse owner that was caused by Streptococcus zooepidemicus, a bacterium commonly found in horses but rarely associated with disease in people. The person didn't have a wound in the shoulder area or any other obvious route for the bacterium to get to the shoulder joint. They searched for a source of the infection and all they found was a chronic lesion on the person's foot. This, combined with the patient's history of taking care of his horses in "bare feet in boots", led them to implicate the foot as the source of infection.

The idea, I guess, is that socks would be a barrier to help prevent contamination of the foot wound. That makes sense to a degree - the person could contaminate his foot with S. zooepidemicus from his hands (probably acquired from touching the horse's nose) while removing the boots, or manure could work its way into boots and directly contaminate the wound. Both are possible, but we have to be a little cautious in interpreting these conclusions. However, this is a bacterium that is associated with horses and the foot lesion is certainly a possible route of entry.

Overall, this should be considered an interesting report of a very rare problem, not something that indicates a major concern. However, there are a few good points to take away from this story:

  • If you have a wound or chronic lesion of any sort, make sure you take measures to reduce the risk of bacterial contamination when working around horses. This might be as simple as making sure it's covered by clothing, or something more involved like using an impermeable bandage.
  • Hands are probably the major source of infection transmission, and good hand hygiene is important after horse or stall contact, particularly if you have an underlying disease.

Handling rabies exposure in horses

I received newsletter today from Intervet (a pharmaceutical company) that is targeted at equine veterinarians. One article discussed rabies in horses. It wasn't bad overall, but I thought the section on what to do when a horse might have been exposed to rabies was worth discussing.

The article asks, "If your client suspects that a horse has been bitten by a rabies-infected animal, what should be done?"

Answer: "Contacting you as the veterinarian is always the first step."

Great first step.  A second step that wasn't mentioned should be, "Try to identify and (safely) capture the animal that bit the horse." This is often impossible but certainly worthwhile if it can be done.  However, if you're trying to catch the offending animal, make sure you don't put yourself at risk of exposure to rabies in the process.  If the animal can be caught, it's rabies status at the time of the bite can be determined (either through testing or quarantine). If it can be shown that the animal wasn't rabid, a lot of stress, hassle and expense can be saved.

"If the horse was previously vaccinated... Then isolate and observe the animal for 45 to 90 days (your clinical evaluation will involve gait analysis, radiography and a spinal tap)."

Boosting the rabies vaccine is also a good idea. The next step, however, needs to be contacting local regulatory officials to find out what you have to do. They determine if, how and how long an animal needs to be quarantined - this is NOT the decision of the local veterinarian nor the animal's owner. Most likely, they will recommend a 45 day quarantine for a vaccinated horse, since this is what is recommended in the NASPHV Compendium on Rabies. The discussion of diagnostic testing makes no sense. There is absolutely no indication to perform diagnostic tests on a horse that has been bitten by a rabies suspect. None. There are no tests that can be used to diagnose rabies in live horses (also exposed horses don't instantly develop signs of rabies). Horses should be monitored closely for signs of rabies during the quarantine period, but that's it.

"...and have the client make a list of all people who had contact with the horse."

This is often done when horses have or are suspected of having rabies, but not horses that are potentially exposed. It is done to help public health personnel contact people that may have been exposed to rabies. A horse that was just bitten by an animal is not a risk for transmission of rabies.  (However, keeping a list of people who have contact with the horse after it's been bitten (i.e. durng the quarantine period) - which should be as short a list as possible - is a reasonable precaution in the unlikely event that the horse does develop rabies.)

"If the animal was not vaccinated, your options are to euthanize and perform a postmortem examination of the brain (the only way to definitely confirm rabies)..."

Euthanasia is one of the options that needs to be considered in an unvaccinated horse that has been exposed, which is one of the reasons that identifying the biting animal and testing it is critical, if it can be done. The last part of the above sentence (from the atricle) is complete nonsense. Why would you test the brain of a normal horse that has been euthanized because it's just been bitten by a potentially rabid animal? The horse isn't being euthanized because it has rabies, it's being euthanized because of the likelihood  of it developing rabies weeks to months later. Testing of the brain will tell you absolutely nothing if the animal was only bitten recently.

"...or isolate and observe the horse for six months and develop the human contact list."

Again, this needs to be decided based on discussions with regulatory personnel who are responsible for dictating what is to be done. A six-month quarantine is a pretty standard recommendation for an unvaccinated animal. Creating a human contact list should not be necessary, since quarantine involves severely restricting contact of people with the horse and only a few (ideally one) person would have any type of contact.

The article wraps up with the very true emphasis on vaccinating horses. It's a cheap measure to prevent a relatively rare but invariably fatal disease.

Click image for source.

This Worms & Germs blog entry was originally posted on equIDblog on 05-Jan-10.

Probiotics and obesity

A recent editorial in Nature Microbiology Reviews by Dr. Didier Raoult raised questions about the potential role of probiotics in obesity.  It is based both on studies indicating weight gain in humans and farm animals in probiotic trials as well as some laboratory animal data. The conclusions based on clinical trials for treatment of disease are pretty weak, since while animals or people may have gained weight, that does not mean they gained fat (if you get better because of a probiotic, you gain weight, but that is probably a healthy response and not obesity). There is some interesting lab animal work that shows changes in fat deposition in response to some probiotics, but it's rather preliminary.

It's way too early to declare that consuming probiotics is a risk factor for obesity. Several letters to the Editor were submited by leading probiotic researchers in response to Dr. Raoult's editorial, contradicting some of the statements that were made. Personally, I don't see convincing evidence of a risk but Dr. Raoult's comments should serve as a reminder that probiotics can have broad and poorly understood effects on the intestinal bacterial population, and correspondingly broad and poorly understood effects on the body. That's why probiotics should be scrutinized like drugs, in terms of safety, effectiveness and quality control. If someone is using a probiotic for themselves or their pet for a defined reason and it seems to be working, I wouldn't recommend stopping because of these largely theoretical concerns about obesity. However, we should perhaps think about why we are using probiotics and the potential costs versus benefits. I doubt this is really going to be a major issue but it's a good one to think about.

Horse Strep in a person via a dog

Streptococcus equi subspecies zooepidemicus (usually just called Strep zooepidemicus) is a common cause of infection in horses. It is an "opportunist" that is often found in healthy horses, but which can cause disease in certain situations. While horses are the natural host of this bacterium, sporadic infections and outbreaks are occasionally reported in dogs at cats, particularly in shelters or other crowded situations. Severe (including fatal) pneumonia can occur, as was reported in a recent outbreak in a humane society in Ottawa. Rarely, S. zooepidemicus can also cause infections in people.

A report in the Journal of Medical Microbiology (Abbott et al) describes a serious S. zooepidemicus infection in a person, that was traced back to a dog. The dog lived on a farm that also had horses. It developed pneumonia and S. zooepidemicus was isolated from its respiratory tract. The dog was treated and recovered. However, the dog owner also became ill with fever, headache, a stiff neck and general malaise. Penicillin was prescribed, but the person's condition did not improve and he/she ended up in the hospital. Streptococcus zooepidemicus was also isolated from this person's nose and throat.  When the dog and human strains were compared using molecular tests, they were related. An investigation of the farm was performed, and while all the horses present at the time were negative for S. zooepidemicus, the bacterium was isolated from a healthy dog.

This is a rare situation and one that shouldn't result in too much concern. It does highlight a couple points that are good to remember:

  • Getting cultures is very important for obtaining a diagnosis.
  • Animal contact and pet health should be considered whenever someone is sick with a potential infectious disease. Physicians need to know whether their patients have contact with animals. They need to be told if a sick animal is present so they can consider whether the pet and human illness might be related. Knowing to what someone may have been exposed might speed up diagnosis and appropriate treatment.
  • Rare things are rare, but they happen. We shouldn't focus on rare events but we have to keep our minds open and recognize that strange things happen with infectious diseases.

Who should pay for Hendra virus research?

A proposed levy on horse owners to fund Hendra virus research has been met with opposition in Queensland. It has been suggested that a $25/horse levy in Queensland would provide needed funding for research into this rare but deadly disease, but this has been opposed by some vets and horse owners. One comment in response to the suggestion of a Hendra virus research levy is that the disease kills humans, so it should be publicly funded. However, Hendra only affects humans who have very close contact with horses, so that's a questionable argument. Also, medical research funding is certainly not overflowing, and the odds of a study such as this getting funded this way may be limited because it is so horse-oriented. I run into the same problem all the time with zoonotic disease research grants. Medical agencies don't want to fund it because it's too animal related, while animal agencies don't want to fund it because it deals more with human health.

Who should fund equine research? Should the government (i.e. all taxpayers) be solely responsible, or should some of the responsibility fall on horse owners, who stand to benefit the most from equine research? This is particularly true for a disease like Hendra that is very rare, currently restricted to one region, and only affects horses and people associated with horses. The rarity of the disease means that industry (e.g. vaccine companies) is probably not eager to fund research (because it would not be profitable). The focal nature of the problem geographically may limit interest from national or international groups. These factors could result in failure to do the necessary research to try to control this deadly disease.

This raises broader questions about funding for equine research. Many people and governments make lots of money from horses, directly or indirectly. You'd like to think that since so much money is made off the backs of horses (both figuratively and in some cases literally), that some of the profits would be put back into helping ensure the health and welfare of these animals. A fraction of a percent of the money generated by horses would be a tremendous asset for equine research, and help make great strides in improving the health and welfare of horses.  Unfortunately, such funding is rarely available, and equine researchers are often very limited in terms of the research that can be done with the available dollars. As a researcher, I know the difficulties of finding enough research funding to pay laboratory personnel and grad students, plus perform high quality research. The limited funding that is available is one reason that equine research is now only a fraction of my overall research program. The equine industry as a whole needs to think about its role in research, even if it's from a self-serving standpoint whereby research is funded to help boost performance and profits.

This Worms & Germs blog entry was originally posted on equIDblog on 14-Oct-09.

MRSA outbreak in Dutch horses

At the ongoing ASM-ESCMID conference on methicillin resistant staphylococci in animals, Dr. Engeline van Duijkeren of Utrecht University (The Netherlands) presented a study on an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) in their equine hospital.

From 2006-2008, several horses that underwent surgery at their hospital developed MRSA infections.  MRSA was also isolated from some healthy horses and personnel at the clinic. Early in the process, the hospital was closed for a thorough disinfection and the outbreak stopped, however another outbreak occurred later.  Further study again found people in the clinic that were MRSA carriers. Close to 15% of people in the hospital who handled equine patients were MRSA carriers, which is really astounding when you consider that less than 0.1% of the general population in the Netherlands carries MRSA. When they started testing horses coming into the clinic, they found that 9.3% of horses were carriers when they arrived. Weekly sampling of all hospitalized horses over a five-week period determined that 43% of all horses in the hospital carried MRSA at one point or another during their stay. Additionally, 53% of environmental surface samples were positive for MRSA, which is really not surprising if that many people and horses are carriers.

If horses keep coming into a facility carrying MRSA and people keep getting colonized, MRSA is hard to control. These experiences led the equine hospital at Utrecht to implement more stringent infection control practices to try to contain the problem, but the high MRSA rate in their referral population is going to pose a continual risk.

MRSA outbreaks in horses aren’t new. They’ve been reported by a few hospitals (including ours) and occur in many, many, (many!) more without ever being published. Since MRSA is present in the horse population, equine hospitals are at continual risk of MRSA outbreaks. If a large percentage of horses in the general population are carriers, the risk of outbreaks is higher.

MRSA is clearly a problem in horses in many areas. It’s important to realize that it’s a problem in the general population, not just horses in hospitals. Equine hospitals can amplify the spread of MRSA, but ultimately a lot (if not most) MRSA-positive horses originate from farms, not clinics or hospitals. Equine hospitals need solid infection control programs to reduce  the risk of outbreaks, but the risk will never be completely eliminated. Farms need good infection control programs to reduce the risk of spread of MRSA between horses and between farms, as well as from horses to people (and back). Antibiotics need to be used prudently since antibiotic use is a risk factor for MRSA carriage and infection.

More information about MRSA in horses can be found on the equIDblog Resources page.

This Worms & Germs blog entry was originally posted on equIDblog on 26-Sep-09.

Hendra virus vaccine: For horses or people?

In the wake of the death of Dr. Alister Rodgers from Hendra virus, there have been increasing calls for the Australian government to put significant resources into Hendra virus research. Various areas need to be investigated, including how this virus is maintained in the bat population, how it is transmitted from bats to horses, ways to treat infection and ways to prevent infection. Vaccination is an obvious topic, and creation of a vaccine appears to be possible. However, as I wrote the other day, there's a question about whether a company would put millions of dollars into development of a Hendra virus vaccine for people, given that the disease is very rare, is currently limited to one region, and only appears to be a risk for people in close contact with sick horses.

One thing that needs to be considered is whether it may be better to develop a vaccine for horses rather than people. Think about it:

  • All reported human Hendra virus infections have come from people in close contact with sick horses.
  • Human vaccines are very expensive to develop, test, get approved and market.
  • Vaccines for animals are much cheaper to make because testing and regulatory requirements are not as strict. (This can lead to marketing of vaccines for animals with limited evidence of effectiveness, but the upside is that vaccines can get to market quicker and with less expense.)
  • People are often more willing to get their horses vaccinated than to get vaccinated themselves.

So, even though it might sound strange, development of a Hendra virus vaccine for horses may be a more effective way to protect people.

If this approach is taken, a key step would be continued research into the epidemiology of Hendra virus infection to investigate other routes of human exposure. If people can get infected by other routes, vaccination of horses obviously wouldn't address the entire problem. However, based on what we know currently, vaccination of horses might be the most effective, timely and economic response to this pressing problem.

This Worms & Germs blog entry was originally posted on equIDblog on 04-Sep-09.

Horse bites

As a vet, I've been bitten by a wide range of animal species. When people talk about animal bites, they usually think about dogs and cats. Horses can (and do) bite as well. Most horse bites are probably playful nips that hurt a little yet don't cause major problems, but some bites can cause serious injuries and infections can result.

A recent paper in the Journal of Agromedicine (Langley and Morris 2009), with the rather unwieldy title of "That Horse Bit Me: Zoonotic Infections of Equines to Consider after Exposure Through the Bite or the Oral/Nasal Secretions". Bites apparently account for 3-4.5% of the approximately 100 000 annual emergency room visits in the US that are associated with horses. The authors of the paper review infections associated with bites and contact with organisms in the mouth and nose of horses.

A large number of bacteria have been associated with horse bite infections in people, including Actinobacillus, Streptococcus, Psuedomonas and Staphylococcus species. Some viruses can theoretically be transmitted by bites, but there's little evidence that this actually happens.

Although viruses are not of as much of a concern overall, rabies needs to be considered in every bite from a mammal. We pay a lot of attention to rabies with dogs, cats and wildlife, but it often gets ignored with horses. While I'm not aware of any reports of rabies transmission from horses to humans by a bite, it could happen.  Fortunately, rabies is rare in horses so the likelihood of exposure from this species is very low. However signs of rabies aren't always obvious initially, and rabies in horses may mimic other diseases. Sometimes, rabies looks like colic, and human exposure through bites or other contact is possible when handling, evaluating and treating affected horses.

Unlike with dogs and cats, there are no clearly defined protocols for dealing with bites from horses. Any dog or cat that bites a person is supposed to be quarantined for 10 days. The reason for this is if the animal is rabid and the disease is advanced enough for the animal to be capable of spreading rabies virus, it would invariably develop signs of rabies and die within this time period. We don't have similar guidelines for horses. I suspect the 10 day observation period would be adequate but we don't have good data. The paper states that in Kentucky, a 14 day observation period has been used by the state Department of Public Health.

At the conclusion of the paper, the authors make a few important general recommendations for reducing the risk of disease transmission from bites and oral or nasal secretions of horses:

  • Use good general hygiene, especially hand hygiene, after any contact with horses.
  • Use gloves and gown or lab coat when examining horses in a veterinary clinic or hospital. (This might be overkill for all horses. We don't require gloves for every horse contact, just contact with mucous membranes (e.g. mouth, nose), wounds, incision sites and other high-risk areas. I think bare hands are fine for general contact as long as there is good attention to handwashing after.)
  • Consider mask and goggles if the horse is coughing or sneezing.
  • Develop standard operating procedures for handling sick horses.
  • Use isolation when needed.

I'd add a few more points:

  • Avoid bites. Pay attention to what you are doing around horses to reduce the risk of being bitten. Do not encourage playful behaviours (e.g. nipping) that could lead to bites.
  • If you are bitten and it breaks the skin, clean the site thoroughly with soap and water. If there is significant trauma, or if the bite is over a joint, hand, foot, or a prosthetic device, you should see a doctor immediately because antibiotics are most likely indicated. If you have a weakened immune system, you should be evaluated by a doctor after any bite.
  • Avoid contact with the horse's mouth or nose if you have skin lesions. Cuts and scrapes can allow bacteria to enter your body and cause infections. If you have a cut on your hand, make sure it is covered with a glove or waterproof dressing if you are going to have contact with the horse's mouth or something that came from its mouth (e.g. a bit).

This Worms & Germs blog entry was originally posted on equIDblog on 02-Sep-09.

Hendra virus claims life of veterinarian

Unfortunately, Dr. Alister Rodgers, who had been hospitalized with Hendra virus infection acquired from a sick horse, died yesterday in a hospital in Brisbane, Australia. He was infected last month while treating an infected horse on a farm that was subsequently identified as having multiple horses infected with the virus. Despite experimental ribavirin treatment, he developed the infection three weeks later. He is the second veterinarian from Queensland to die from Hendra virus infection in a little over a year. Four of the seven people known to have been infected by this virus since it first emerged in 1994 have died.

"Horse strep" in people

I received the following question the other day: "I have a friend who had chemo embolization on tumor on liver in late June. She is in hospital now, and an abscess was discovered on liver.  Pathology results said "equine strep".  Her brother visited immediately after procedure, and he works with horse full time."

Streptococcus is a group of bacteria that includes many different species. There are two main species in horses Streptococcus equi subsp. equi (aka S. equi, the cause of strangles) and Streptococcus equi subsp. zooepidemicus (aka S. zooepidemicus, a cause of various types of infections). As you can guess by the 'equi' name, their natural host is the horse. Strep infections are very common in people, but rarely involve these two species. Nonetheless, infections with either Streptococcus equi or S. zooepidemicus can be found in people, but S. zooepidemicus is most common. Usually, these infections develop in people who are already sick for another reason, have compromised immune systems, or in young children. Interestingly, not everyone that is infected reports direct or even indirect contact with horses.

Back to the question: it's hard to say what's going on here based on the the general term "equine strep", but presumably the person has an infection with S. equi or S. zooepidemicus. Whether horses are actually involved will be tough (or impossible) to determine. It's a tempting hypothesis that the patient's brother carried the bacterium from the farm to the hospital, but I'd be wary about making a definitive statement about the bacterium's origin solely based on that. There are ways to investigate this further, such as trying to isolate Streptococcus species from horses on the farm, typing them and comparing them to the strain that caused disease in the person, but this type of testing is very costly and almost never performed, as human infection with these species is so uncommon.

This should be a good reminder that people who are sick and in hospital are at higher risk for developing infections, and they can get infections from bacteria that rarely cause disease in healthy individuals. While there is no proof of a link to horses (at least in this case), good infection control practices should be used whenever anyone visits someone in the hospital. That would include not wearing barn clothes to the hospital and paying close attention to handwashing.

This Worms & Germs blog entry was originally posted on equIDblog on 26-Aug-09.

Veterinarian diagnosed with Hendra virus infection

A veterinarian, one of four people in Australia that were under close observation due to exposure to a horse with Hendra virus infection, has developed signs of infection.  Dr. Alister Rodgers is now in hospital in critical condition. He had close contact with a sick infected horse three weeks ago - Hendra virus was not considered initially, it was thought that the dying horse had been bitten by a venomous snake. Dr. Rogers didn't wear gloves or a mask when examining the horse because he had left them in his car.

Dr. Rodgers received experimental treatment for five days to try to prevent or reduce the severity of infection. He had returned home from hospital following the treatment only one day before he became ill. It has now been confirmed that he is infected. Only six people have been previously diagnosed with this rare disease; three have died. There were hopes that all of the exposed individuals would escape unscathed given initial tests showing no sign of infection and the experimental therapy, but it's clear now that early detection of infection is not easy.

Image: Coloured electron micrograph of Hendra virus (source:

This Worms & Germs blog entry was originally posted on equIDblog on 21-Aug-09.

Rabid horse in Maryland

A horse in Harford county Maryland has been euthanized because of rabies. The horse first starting showing signs of disease in mid-July, which manifested as "striking changes in behaviour." The report doesn't say when the horse died, but animals typically die within a few days of the onset of neurological disease. The horse was transferred to the New Bolton Center where rabies was diagnosed. Subsequent testing showed it was a raccoon rabies strain, although that does not mean that a raccoon was the actual source of infection.

Public health officials implemented a 45 day quarantine of the farm. Stray cats (about 25) were caught and euthanized. Fortunately, the family pets were properly vaccinated and have received booster shots (plus presumably a period of observation at home... a much better situation than if they were not vaccinated).

People that had contact with the horse have received rabies post-exposure treatment. This includes one person who had to be tracked down overseas.

Harford County Health Department spokesperson Bill Wiseman said "There was never a risk to public safety. This incident was a great example of public health work in action and cooperation between local, state and in this case, international authorities." I don't buy the statement that there was no risk to public health. While the risk of rabies transmission from infected horses is very low, it's not zero. Rabid horses have killed people because of their abnormal and sometimes aggressive behaviour. Further, the fact that this horse had rabies means that it got it from something. Rabies can have a long incubation period so it's not guaranteed that it acquired it on the farm, but you have to be prudent and assume that there is infected wildlife in the area that could pose a risk for other animals or people. Public health authorities managed the situation well and reduced the public health risks, but there were certainly still risks.

Rabies vaccination is highly effective. There is no statement about whether this horse was adequately vaccinated but it's unlikely. Proper vaccination would likely have prevented this horse's death, as well as the death of the stray animals, cost of vaccination of people, cost of veterinary care for this horse, quarantine of the farm and the associated financial and emotional costs. A dose of vaccine that costs a few dollars could have saved thousands of dollars and emotional stress.

Rabies is a rare disease in horses but its severity means it should not be ingored. Vaccinate your horses.

This Worms & Germs blog entry was originally posted on equIDblog on 14-Aug-09.

Experimental treatment for Hendra virus-exposed horse personnel

Four people exposed to horses infected with Hendra virus in Australia are taking an experimental drug to try to prevent or reduce the severity of infection. All are currently healthy, but it is unknown whether the virus is incubating in them and whether disease may develop.  People can be infected with this virus through close contact with infected horses, as was the case with these four individuals. While human infections are rare, 50% of infected people die. Therefore, it's understandable that they would choose to try an experimental treatment.

These people will be treated for five days with intravenous ribavirin, an antiviral drug. There is evidence that ribavirin can kill Hendra virus in the laboratory, but it's not known if it actually does anything in infected people. It has some potential adverse effects, but given the severity of disease and high risk that these people have been exposed, it's certainly a reasonable decision. This treatment was also used in the Hendra virus outbreak in 2008. One person died, one survived after a long stay in ICU, and one did not get sick.  It's not known whether the drug did anything to help. The death of the treated person doesn't necessarily mean the treatment is not useful for some people or for certain stages of infection. Hopefully, ribavirin has a better chance of working when infection is only developing, before these people get sick.

This Worms & Germs blog entry was originally posted on equIDblog on 13-Aug-09.

It's back: Hendra virus in Australia

Hendra virus, a virus that can kill horses and people, has resurfaced in Queensland, Australia. This bat-borne disease has caused periodic fatalities in horses and people that work with horses. The latest outbreak is thought to have killed up to three horses and resulted in the potential exposure of at least 30 people. The likelihood of these people getting sick depends on how close their contact was with the sick horses. Close contact with secretions from infected horses seems to be required to transmit disease. One person reported being snorted on by an infected, dying horse and being "covered" in blood, which is certainly concerning. An outbreak last year killed a veterinarian and hospitalized a veterinary nurse.

The farm in question is under quarantine and people that have been exposed are being monitored. There is no treatment for potentially exposed individuals, so they are in the unenviable position of having to wait and see if they get sick.

A virus like this is very hard to control. It's lives in fruit bats and only occasionally crosses into horses. The sporadic nature of disease makes it hard to control and predict when cases will occur. The key is early identification so that there is minimal exposure to other horses and people. People also need to take routine infection control precautions. One veterinarian handled an infected horse without using gloves or a face mask, as recommended, because he had left them in the car. Exposure to a potentially fatal infectious disease is not worth the few minutes of time saved by not following recommended precautions.

This Worms & Germs blog entry was originally posted on equIDblog on 10-Aug-09.

Horse ownership and tetanus exposure

Here's a question I received the other day:

"Do people who work with animals and who work in barns need a tetanus shot as a result of this type of work?  We have Therapeutic Riding Programs in the region and there is a sense that perhaps the volunteers and those who frequently tend the horses need to receive this.  Is this the case?"

Tetanus is a disease that we are quite concerned about in horses because horses are very susceptible to it. That's why we vaccinate them yearly. Tetanus can also affect people, but very rarely because of vaccination and because people have lower susceptibility to the disease. While we pay a lot of attention to tetanus in horses, this does not mean that being around horses increases a person's likelihood of exposure to tetanus. The bacterium that causes tetanus, Clostridium tetani, lives in soil and commonly present in the environment. The more environmental exposure that you have (especially to soil), the greater your risk of exposure to C. tetani. Being around horses doesn't increase your risk any more than doing other things outside.

Whether you have contact with horses or not should not change your approach towards tetanus prevention. You should be vaccinated against tetanus every 10 years. Many (probably most, actually) adults are not up-to-date on tetanus vaccination. Adults tend not to get booster shots on schedule, and often only receive them when they have had a wound that requires medical care. For example, If you get stitches, the medical staff will almost certainly inquire about your last tetanus shot, and give you another one if you haven't been vaccinated in the past 10 years (or if you can't remember).

More information about tetanus in horses is available on the equIDblog Resources page.

This Worms & Germs blog entry was originally posted on our sister site, equIDblog, on 10-Jul-09.

Bug of the Month: Equine Infectious Anemia Virus

Equine infectious anemia (EIA) is a rare disease but one that a lot of time, effort and money are put into avoiding. Most people know about this disease by way of the most common test (formerly) used to diagnose it: the Coggin's test (see image).

Equine infectious anemia is caused by a virus of the same name ( equine infectiious anemia virus, EIAV). EIAV is a lentivirus which, like all other lentiviruses, causes persistent infection. Unlike most other lentiviruses that cause slow, gradual preogression of disease, EIAV infection usually causes a sudden onset of disease (acute phase) followed by recurrent disease. After the initial (acute) phase, horses can appear normal, which means they can be a silent reservoir of the disease. That's why routine testing for EIAV is required in many circumstances: to detect silent carriers so they cannot continue to transmit infection.

Signs of acute EIA vary, but usually include fever, lethargy and decreased appetite. Anemia (decreased red blood cell count) and thrombocytopenia (decreased platelet count) can be detected. Anemia is more common and pronounced with recurrent infections. Intermittent illness often develops after the first acute episode. Affected horses may experience short (3-5 day) periods of fever, lethargy and decreased appetite. The severity of the anemia often correlates with the severity and frequency of these disease episodes. In some horses, these episodes are very common, long and severe, and these horses often have severe weight loss and anemia. However, most infected horses stop developing obvious signs of disease after a year and seem perfectly healthy.  This may be good for the one horse, but it's bad for other horses in the area to which the virus may be transmitted.

EIAV is a bloodborne virus that can be transmitted by blood-feeding insects, especially tabanid flies (horseflies, deerflies). Stable flies can also transmit EIAV but do so less effectively. Contaminated medical supplies such as reused needles and syringes can also transmit EIAV.

Fortunately, EIA is now rare in most regions and positive tests are quite uncommon. Routine testing for EIA is usually required for shows, sales, transportation and other situations where horses are mixed, in order to detect and remove carriers. Unfortunately, identification of a horse as a carrier is not good for the horse or owner (or other horses in the area) - EIA is not treatable, and horses that have positive tests ("reactors") are quarantined, as are all other horses that are housed within 200 yards. Horses living close to reactors are tested (usually 30 and 60 days after removal of the reactor) and only released from quarantine after getting negative test results at least 60 days after the last reactor was removed. Reactors are usually euthanized. If prompt euthanasia is not chosen, reactors are usually prominently branded or tattooed. They must be kept under quarantine for the rest of their lives, and at least 200 yards from other horses. (200 yards is used because the flies that transmit the disease don't usually travel that far.)

The best way to reduce the risk of EIA is ensuring that all horses are regularly tested. New horses coming onto a farm must be tested BEFORE arrival or after arrival but while in quarantine at least 200 yards away from other horses. Needles and other items that might be contaminated with blood should never be re-used, both due to the EIA risk and to avoid other potential problems.

Overall, EIA is a very rare disease, but the severe implications of a positive test mean that we need to be vigilant.

Image from

Rhodococcus equi in horses and people

Rhodococcus equi is a very well recognized pathogen in horses – it is a common cause of pneumonia in foals between the ages of 1-6 months, and infection is also sometimes associated with other problems such as diarrhea, swollen joints and abscesses in other parts of the body. The infection can be very difficult to treat because the bacteria are able to live inside white blood cells, which helps protect them from the body’s immune system, and because they often cause abscesses to form, which are difficult for antibiotics to penetrate. Rhodococcus equi infection in foals has been studied extensively, but there’s still a lot we don’t know how the body defends itself against this organism.  These are a few things we do know:

  • Almost all foals are exposed to R. equi as neonates, but most of them never develop signs of infection.
  • Giving newborn foals hyperimmune plasma (plasma with extra antibodies against R. equi) may have some beneficial effects on farms where the infection is a recurrent problem, but this practice is still controversial.
  • Adult horses are essentially immune to the infection.
  • In almost all cases if clinical disease in foals, the R. equi strain involved carries a special gene called vapA.
  • Mortality rates in foals vary considerably from 0% to 30%.
  • So far, efforts to develop a vaccine to help protect foals have been unsuccessful, but research in this area is ongoing.

People can also be infected with R. equi, and as in foals, pyogranulomatous pneumonia (infection of the lungs which results in the formation of many abscesses) is one of the most common conditions caused by this organism. However, there are a few important differences between infection in people and infection in horses:

  • 85% to 90% of people with R. equi infection are immunocompromised, meaning their immune system is weakened or suppressed for some reason, e.g. HIV infection, or immunosuppressive drugs taken by organ transplant or cancer patients.
  • Among people infected with R. equi who have normal immune systems (i.e. immunocompetent), about half of the infections are localized, meaning they only affect one small part of the body. Many of these are associated with wound infections.
  • Only 20% to 25% of the R. equi isolates in people carry the vapA gene.
  • Infection in immunocompetent people can be fatal in approximately 11% of cases, but among HIV-infected patients the mortality rate from R. equi infection can be as high as 50% to 55%.

Rhodococcus equi is actually a soil organism, and this is likely the most common source of the organism for both horses and people. Only approximately 1/3 of humans infected with R. equi report that they have had contact with horses or pigs (pigs can also carry the bacterium). So we don't know how much of a risk an infected foal is to a person.  However, it is prudent for people, particularly those with weakened immune systems, to take precautions to avoid potential transmission of R. equi from horses.

  • Try to reduce dust levels on the farm. Because R. equi most often lives in the soil, it can get stirred up into the air in dusty areas, which can then lead to inhalation by animals and people. Doing things like planting grass or other vegetation, installing windbreaks in high-traffic areas, or wetting down dusty stalls or paddocks can help reduce dust levels in the air.
  • Keep open wounds and other broken skin covered when working around animals.
  • Always wash your hands after handling a foal (or any horse)
  • If you have a foal that develops signs of R. equi infection, make sure you have your veterinarian examine it as soon as possible so the diagnosis can be determined and the foal can be treated properly as soon as possible. Some foals with R. equi may develop severe pneumonia very quickly, so it’s important that they are examined right away.

Climate change and pet health

Recently, I made a few comments about climate change and the potential impact on infectious diseases in horses on our sister site, equIDblog. A recent news article in New Scientist discussed concerns about climate change and pets. The main infectious disease concern regarding climate change is changes in patterns and spread of insect-borne diseases, because different insect vectors may expand their normal ranges or change their seasonality in response to climate change. Some of the examples cited in the article include:

  • Babesiosis, a blood-borne disease spread by the European dog tick, is being found in areas of Europe where it was previously rare.
  • Increasing populations and ranges of ticks have been reported in many countries, which is a significant concern based on the number of different diseases these ticks can carry and transmit.
  • Leishmaniasis has been identified in dogs in the southern UK.  If climate change allows sandflies (the insect vector of this disease) to become established in the UK, then spread of this disease could become a major problem.
  • Milder winters may result in longer periods of activity of some insects that transmit disease, thereby extending the times of the year when there is a risk of disease. In some areas, year-round risk could develop for diseases that were previously seasonal.

Climate change is a complex and still rather controversial topic. Predicting the infectious diseases implications of climate change is difficult.  Information that is already available for some diseases, combined with general knowledge about microorganisms and their hosts, can help us make some educated guesses about what may happen. While the full scope of the impact cannot be predicted, it is almost certan that climate change will result in infectious disease challenges in both veterinary and human medicine.

Service monkeys and horses...where do we stop

I was at the annual conference of the Society for Healthcare Epidemiology of America on the weekend. This is a hospital infection control organization, and one of the talks I gave was about animals in healthcare facilities. One question that came up was about unusual service animal species like monkeys. Service animals are specially trained animals that help disabled individuals with specific tasks. The most common examples are seeing-eye dogs. In the US, the American Disabilities Act protects service animals and dictates that they must be allowed to go wherever the person goes. I don't think people have a problem with that in general. However, there are concerns with respect to non-traditional species being used in these roles, and the question at the meeting was about service monkeys. Monkeys can be incredibly strong physically, and they can carry some important infectious zoonotic diseases, so there are concerns about them being allowed in hospitals. Part of the issue is what really makes an animal a service animal.  Should all animals that help someone out (in any capacity) be considered service animals?

That same topic came up in a recent ABC News article that described a seeing-eye horse in Texas, including a video of the owner riding the horse while grocery shopping. 

I have no doubt that this horse helps out its owner and provides great joy, if not increased freedom. However, I'm not convinced that a horse is necessary to fulfill this person's need for a service animal. Why use a horse when a dog could do as good (or a better) job? How was the horse trained? Was it trained under a formal program so that it is truly helpful? What types of health and behaviour screening have been used? What are the additional risks associated with using such a large farm-animal species?

Horses, even based solely on their size, can easily cause injury to members of the public without meaning to, simply by stepping on a person's foot or bumping into them, for example.  Some people might be scared of horses, especially indoors. Horses aren't litter trained, and horse manure can carry potentially infectious agents. I have a big problem with the video of this horse in a grocery store.  At end of the day, is a horse really necessary for what this person needs, and has the horse been adequately evaluated to ensure that it is low risk to the public? I don't think the answer is yes to either question, let alone both.

We certainly must do all that we can to allow full access of appropriate service animals, but we also need ensure that novelty "service" animals don't cloud the picture and potentially have a negative impact on true service animals.  The article states "...the government has begun rethinking whether the regulations should be changed to exclude some animals." That sounds like a great idea to me. Careful review of this issue, including the benefits to people, risks to the public and the need for new species over traditional options all need to be considered. 

Image: captured from video at

Testing for ringworm with toothbrushes

If your veterinarian suspects your pet may have ringworm, there are several different ways he or she may test for the causative fungus (a dermatophyte) on your animal's fur and skin.  Some of these techniques are more useful than others in different situations.

  • Wood's lamp:  A Wood's lamp is simply a special ultraviolet light.  Approximately half of all Microsporum canis strains (the most common species of dermatophyte that causes ringworm in cats and dogs) will fluoresce blue-green under such a light. This type of testing is obviously very easy to perform.  However, other debris in an animal’s hair coat may fluoresce as well, and other species of fungus that cause ringworm do not fluoresce, so this test is not useful by itself in most cases.
  • Microscopy: Sometimes ringworm fungus can be seen on hair shafts from an infected pet when examined under a microscope.  However, it is easy to confuse other debris and structures for dermatophytes.  Also, not every hair on an infected animal will carry the fungus, so it's possible to miss the infected hairs altogether with this test.
  • Fungal culture: The best way to diagnose ringworm is to culture the fungus from the infected individual (person or animal). In animals, one of the best ways to collect a sample for culture is to comb over all the fur and skin with a new toothbrush, and then try to grow dermatophytes from the toothbrush. This allows the fur from all over the animal to tested, rather than just one little clump of fur plucked from one area.  It can also make it easier to get a sample from the face and paws of cats, which is where these animals often carry the fungus.  Although fungal culture is the best way to diagnose ringworm, remember that fungal culture takes much longer than bacterial culture – instead of days, it may take up to three weeks to grow some dermatophytes.

It's also important to remember that dogs, and more often cats, may carry dermatophytes on their fur even when they look healthy.  A positive fungal culture from an animal with skin disease, particularly a cat, does not necessarily rule out other diagnoses, so your veterinarian may still recommend other tests as well.  However, any animal with ringworm should be treated to prevent spreading the infection to other animals and people.

More information about ringworm is now available on the Worms&Germs Resources page, and in our archives.

Molecular Diagnostic Testing: Pros and Cons

An important step in diagnosing infectious diseases and determining the optimum approach to treatment and management is rapid and accurate diagnostic testing. Many different testing methods are used, particularly bacterial culture (at least for bacterial diseases). Molecular testing has revolutionized the field of microbiology, and is making inroads into the field of diagnostic testing. Polymerase chain reaction (PCR) testing is a very powerful tool that can be used to detect DNA or RNA from specific microorganisms.  This technique can be very useful, but it can also be easily misused or misinterpreted.

The potential PROS of molecular diagnostic testing include:

  • Rapid turnaround time: Testing can take as little as a few hours versus a few days for other tests like bacterial culture.
  • Sensitivity: Organisms that are difficult or impossible to grow in a lab can be detected, and they can often be detected at lower levels than with other diagnostic methods.

The potential CONS of molecular diagnostic testing include:

  • Sample contamination: This is a common concern with highly sensitive molecular tests - even a minute amount of contamination in the sample can cause a false positive result.
  • Test inhibition: Samples from complex biological sites (e.g. stool) can contain substances that interfere with the many complex molecular reactions upon which the tests rely. Without good (and proven) methods to prepare the sample, this can result in a false negative result.
  • Biologically irrelevant results: Some bacteria that cause disease are also commonly found as part of the normal microflora in healthy animals - simply finding it does not tell you that it is necessarily relevant to the problem. For example, Clostridium difficile can be found in the intestine of approximately 10% of healthy dogs and cats (or more, in some situations), but the diagnosis of C. difficile diarrhea requires detection of the bacterial toxins in stool samples, not just the bacterium itself.  A molecular test that simply identifies the presence of C. difficile, even if it identifies strains that possess the genes to produce toxins, tells you nothing about whether the bacterium was actually producing toxins in the animal.
  • Lack of validation: This is a common problem with many (if not most) molecular tests. Some companies, especially those that just run molecular tests, offer a huge array of completely unvalidated and sometimes illogical tests.  It is also important to remember that tests must be validated for each species in which they are used - a test that works well in people will not necessarily work on a sample from a horse or a dog.

Molecular testing can be useful in some situations. If you are unsure, here are some things to ask the lab:

  • Do they have a validated test that provides relevant results?  If they don't have good data (ideally published data) that their test is useful, accurate and reproducible, I'd avoid it.
  • Do they have a quality control program, which includes running positive and negative control samples with each test batch?

Finally, as with any test that we use in veterinary (or human) medicine, it's important to evaluate all  results in the context of what is happening with the animal - treat the patient, not the test result.

Rabies Vaccination in Horses: Core Issues

In 2008, the American Association of Equine Practitioners (AAEP) published updated vaccination guidelines for horses.  One of the changes from the previous set of guidelines was the inclusion of rabies as a core vaccine (meaning every horse should receive it).  There was lots of discussion about this at the recent AAEP Annual Convention in San Diego, CA.

Some veterinarians don't like the idea of vaccinating every horse against rabies.  Just like veterinarians and owners of dogs and cats who are concerned about over-vaccination in these species, the same concerns exist in equine medicine.  Equine rabies vaccines are not approved for use every three years like some canine and feline vaccines, so they still need to be given every year until someone can determine for how long a vaccinated horse is protected from infection.   Furthermore, there has never been (to my knowledge) a case of human rabies due to transmission from a horse.  These are all valid points, but there are also a lot of reasons why including rabies as a core vaccine for horses is very good idea:

  • Rabies is a very deadly disease, in both animals and people.  To some owners, their horse is every bit a part of their family as any dog or cat could be.  To other owners, their horses represent a great investment, and part of their livelihood.  Even if the risk of disease in horses is low, protecting them is safe and easy, so it just makes sense.  As the saying goes, an ounce of prevention is worth a pound of cure, but when there is no cure and prevention is so simple... you do the math.
  • Rabies vaccination is extremely effective in horses, producing an excellent immune response even with a single dose.  It does not require complex adjuvants that some other vaccines need to stimulate the immune system, which also makes it less likely to cause an abnormal vaccine reaction.
  • Rabies is not a seasonal disease like many of the respiratory viruses or insect-borne diseases (e.g. West Nile) for which horses are also typically vaccinated.  Rabies boosters only need to be given once a year, so this can be done during a time of year when no other vaccines are required, if there are concerns about giving too many vaccines at once.
  • Horses live outside and in barns.  Most are far less supervised than dogs and cats, but even these animals are at risk of rabies exposure.  A rabid animal could easily be "brave" enough to attack a horse, even though it normally wouldn't.  Bats can also easily get into and out of many barns - you may never know one was there, and finding a bite mark from a bat on a horse would be like looking for a needle in a haystack, but that's all it takes to transmit the virus.  So it makes sense to give your horse added protection by vaccinating it.
  • Rabies in horses may not look like rabies at first.  One of the most common early signs is actually colic.  A rabid horse that looks like a colic may expose the people who are trying to look after it before they realize what the horse has.  In other horses the signs may be recognized too late, like the rabid horse that was found at the Missouri State Fair earlier this year, that resulted in exposure of many people.
  • While rabies transmission from horses to people has not been documented, rabid horses have killed people, particularly horses that develop the "furious" form of rabies, which can cause them to become very violent.

For more information on rabies, see our rabies archive or the information sheets available on the Worms & Germs Resources page.  For more information on rabies in horses specifically, visit our sister site,

Pet pharmacies: the good, the bad and the ugly

I spent some time the other night looking at different internet pet pharmacy sites. (Yes, I know that sounds strange, but it was interesting and sometimes appalling.) It's well known that you can buy virtually anything over the internet. Pharmaceuticals are no different. There are numerous online pharmacies that offer drugs for animals. Some are presumably highly reputable companies that do what they are supposed to do: dispense drugs only with a valid prescription from a veterinarian, dispense only drugs that they can sell legally, and ensure that everything they sell is of appropriate quality.

However, it's clear that not all pet pharmacies are equal. Most state that a prescription is required, yet it is unclear how many actually follow this requirement. Some will have their own veterinarian write the prescription (which is illegal because the vet would not have a valid relationship with you and your pet, and would not have examined your pet). Some sites offer products that members of the general public cannot legally obtain or possess in most areas, like rabies vaccine. Virtually all the sites offered a wide range of antibiotics. Few had information about the origin of the products or shipping issues to other countries.  Import regulations are very important because, for example, an individual cannot legally import vaccines into Canada.

Certain things raised some big red flags on some sites:

  • No indication of where the pharmacy is geographically. (I'm sure this is because if they don't say they are from a particular country, then it is less likely that the regulatory authorities in that country will look at them.)
  • No information about shipping issues.
  • No clear statement about how they verify valid veterinary prescriptions.
  • Offering a very wide range of drugs, including things like rabies vaccine and narcotics which are not legally obtainable by the public.
  • No contact information.

An article from the FDA also has some good points to consider.

Online pharmacies are very much a "buyer beware" situation. The last thing you want is to buy important drugs like antibiotics online and not be certain that you are actually getting the real thing. Counterfeit drugs have been obtained from some of these websites.  If you're treating your pet with an ineffective "fake" antibiotic, your pet's infection will only get worse, and your pet may develop more severe complications.

If you are going to use an internet pharmacy, do some research first, and talk to your veterinarian (you'll need a prescription from him/her anyway).

Healing with honey

As we encounter more infections caused by antibiotic-resistant bacteria (e.g. MRSA), we need to explore treatment options other than antibiotics. While we usually focus on "new" treatments, sometimes we can look back in time for ideas to treat infections. An old treatment method that is getting increasing attention these days is the use of honey. Honey may be a safe, effective and affordable treatment option in many cases. Click on the picture below to view a video by Dr. Karol Mathews, a critical care specialist at the Ontario Veterinary College.

Equine infectious diseases

We're happy to announce the launch of a sister site to the Worms & Germs blog. This site, equIDblog (available at, is a resource on equine infectious diseases, and has many similarities to this site, with regular blog posts and a collection of information materials pertaining to equine infectious diseases as well as infection control on horse farms and equine hospitals. If you like horses, stop by!


Flu problems: people vs pets

It's that time of year again - we're coming up on flu season, and the ads on the radio and the television are out, encouraging everyone to get their "flu shot," (aka influenza vaccination).  Influenza isn't just a problem in people - it is a very versatile group of viruses that can infect many different species of animals. 

Equine and swine influenza viruses cause serious problems in horses and pigs, respectively.  Last year there was a massive outbreak of equine influenza in Australia.  Because Australia was previous free of equine influenza, most of the horses there had never been vaccinated against the virus.  Therefore the entire population was very susceptible to the disease and it spread very quickly.  The outbreak has since been brought under control.  A previous Worms & Germs post talked about an outbreak of canine influenza in dogs in Chicago IL this past summer.

Equine and canine influenza (and usually swine influenza) cannot be transmitted to people.  However, there are some strains of influenza that can cross species.  The most well-recognized one is certainly avian influenza (bird flu), which caused outbreaks in a number of Asian countries in 2004.  Although people are much less susceptible to avian influenza than birds, the H5N1strain has caused significant illness and fatalities in people.

A lesser known fact about influenza is that pet ferrets are very susceptible to the virus, including human strains.  This is part of the reason ferrets are often used as animal models of the disease in research studies.  Signs of the flu in ferrets are similar to what you'd expect to see in people - fever, sneezing, runny nose and lethargy.  A pet ferret can both transmit to and catch the flu from a person.  Unfortunately for the ferrets, there is no available vaccine for the flu in these animals.

Lucky for us, people can be vaccinated against influenza.  Most people are still far more likely to get the flu from another person than from any kind of animal.  Getting your flu shot is the best way to help prevent yourself from getting the flu, and spreading it to others.  However, it's important to remember that no vaccine is 100% protective, so it's still important to take a few common-sense precautions, like washing your hands frequently, and sneezing/coughing into the crook of your arm, not into your hands.  (And watch out for sick ferrets!)

There is lots of information about influenza and flu vaccine available on the web, including some of the links in this post, and also on the CDC Influenza (Flu) website.

Eastern Equine Encephalitis - Not Just For Horses

Over 50 horses have died from Eastern Equine Encephalitis in Florida this year. The disease, caused by a virus of the same name, affects the brain, resulting in a broad range of clinical signs from behaviour changes to blindness to irregular gait. The disease is also sometimes called “sleeping sickness” because some horses may become severely depressed, with low head carriage and droopy eyes, ears and lips. Almost all horses that develop neurological signs from this infection die. Only 35 cases were reported in Florida in 2006 and 2007 combined.

There are actually three related equine encephalitis viruses – Eastern, Western and Venezuelan – which are called EEE, WEE and VEE for short. VEE is found in South and Central America and Mexico, and occasionally in the southern United States, but has never been reported as far north as Canada (VEE is a reportable disease in Canada). It is unique among the three diseases as the only one in which an infected horse will carry enough virus in its bloodstream to infect a mosquito, which could then pass the virus on to another animal. The EEE and WEE viruses, just like the West Nile virus, do not reach high enough levels in the bloodstream of horses to do this. The mosquitoes usually pick up the viruses from passerine birds, which do not become ill from the viruses (unlike West Nile virus in birds from the family Corvidae).

People can also be infected by EEE, WEE and VEE. About 10 fatal cases of EEE in people are reported in the United States every year. But horses cannot transmit EEE or WEE to humans, even if they’re bitten by the same mosquito. A higher number of cases in horses, however, may mean a higher number of mosquitoes that are carrying the virus. There is no vaccine for these viruses for humans, but there are vaccines available for EEE, WEE and VEE for horses.

In the end, EEE is just one more good reason to make sure you wear mosquito repellent when you’re enjoying the great outdoors during the summer. Visit the Health Canada website for safety tips on using personal insect repellents. EEE is very uncommon in Ontario, but horses that live in or travel to the southern United States should be vaccinated. Talk to your veterinarian about whether or not your horse should be vaccinated. Remember that fly control is also important for our equine companions (and also helps protect them against West Nile!).

Rabies in the US in 2007

A recent report in the Journal of the American Veterinary Medical Association by Jesse Blanton and colleagues provided a detailed report of rabies infection in the US in 2007. Here are some of the more interesting points:

  • Rabies was diagnosed in 7 258 animals and 1 person. That's a 4.6% increase in animals from 2006, but 2 fewer human cases.
  • 93% of cases were wildlife: 37% raccoons, 27% bats, 20% skunks, 7% foxes.
  • 0.8% of cases were in cattle and 0.6% were in horses.
  • 4% of cases were cats, with the largest numbers of feline cases in Virginia, Florida, Pennsylvania, North Carolina, Maryland, New Jersey, New York, Georgia, Texas and Kansas.  Cat cases peaked in June and July.
  • 1.3% of cases were dogs, with the largest number of canine cases in Texas, Georgia and North Dakota. Dog cases did not appear to have a seasonal pattern.
  • Small numbers of a variety of other species were diagnosed, including pigs, wolves, opossums, bobcats, coyotes, otters, bears, deer, mongooses (in Puerto Rico), groundhogs and beavers.
  • The largest number of rabies cases occurred in Texas (969).
  • The infections that occurred were due to several rabies virus variants in circulation in North America, including raccoon rabies virus, skunk rabies virus, arctic fox rabies virus, bat rabies virus and Texas gray fox rabies virus.  In each region of the continent, one or more of these rabies virus variants may be more common.
  • No infections with canine rabies virus were identified. Dogs and coyotes were infected by other variants of the rabies virus, but not with the dog variant.  It is believed that dog-to-dog transmission of canine rabies virus no longer occurs in the US.
  • The one human rabies case in 2007 occurred in Minnesota, and was probably due to exposure to a rabid bat.

More information on rabies can be found on the  Worms & Germs Resources page, and in the rabies archives.


Chloramphenicol: the good, the bad, and the "beware"

As we see more and more infections caused by antibiotic-resistant bacteria, we have to re-think our approach towards antibiotic therapy. This often involves using new drugs, but sometimes it also involves considering the use of older drugs that we haven't used very much for a long time.

One such drug is chloramphenicol. Years ago, this antibiotic was widely used, and is still used in people and animals in some situations. In some respects, it is a very good antibiotic - it is often effect against many bacteria including those that are resistant to many other drugs, such as MRSA and MRSI/MRSP.  Chloramphenicol can also be given orally, and it's relatively cheap. Unfortunately this drug can also be very toxic, both to the animals being treated with it and to people that come in contact with with it in the process. In some animals, chloramphenicol can cause suppression of the bone marrow, where red and white blood cells are produced. This is more of a concern with long term use, but if the bone marrow does become suppressed, stopping treatment with the chloramphenicol typically resolves the problem.  Unfortunately, this bone marrow suppression is much more of a concern in people - the supression is very severe, and can occur with exposure to even a very low dose (or probably single dose) of chloramphenicol.  This results in a condition known as aplastic anemia,  which it typically fatal.  Fortunately this reaction is very rare in people, but there is no way to predict who might develop this condition, and since it is usually fatal, we obviously need to be cautious about using this drug. In some countries, chloramphenicol use in banned in all animals. In many others, it cannot be used in food animals, but can be used in pets.

  • Chloramphenicol should only be used as a drug of last resort. There are situations where it is useful and may be life-saving, but the human health risks cannot be overlooked.
  • If chloramphenicol is being considered, it is critical that  people who would need to handle the drug understand the risk and how to safely handle the drug to avoid exposure.
  • Chloramphenicol tablets should not be crushed or otherwise processed at home because of the potential for breathing in the drug when it is in powder form.

Direct contact with pills or liquids should be avoided by use of gloves or other safe handling practices.

  • If a liquid form is used and is squirted onto food, the food bowl should be handled as if it is contaminated.
  • If pills are being used, the animal should be observed to ensure that the pill is ingested and not spit up and left on the floor.
  • Contact with the mouth and face and animals that are being treated with chloramphenicol should be avoided in case drug residues are present.

If people are unable or unwilling to follow safe handling recommendations, they should not use this drug.

Ringworm Part 2: Cleaning Up

For more information on ringworm, see the Worms & Germs post Ringworm: Skin fungus by any other name.  The photos here show ringworm lesions on a person's arm and on a cat's face, respectively.  (Photo credits: A. Yu, Ontario Veterinary College)

Over the past several years, studies have shown that many environmental disinfectants sold and labeled for use against the fungi that cause ringworm (which are called dermatophytes) in animals and people are, in fact, not effective when used in households and veterinary clinics.  The problem is the chemicals are typically tested against a suspension of the organisms in a test tube, but in the “real world” the fungi are usually found on small fragments of infected hairs.  Its possible that the hair shaft protects the fungus from the actions of some disinfectants.

There are a few disinfectants that have been shown to be effective against dermatophytes even when they are found on infected hairs and skin cells in the environment.  The most readily available one is household bleach, used at concentrations of 1:10 to 1:100.  Other effective products include Virkon-S® (a detergent-peroxide based product) and Peroxigard® (an accelerated hydrogen peroxide product) . An environmental spray containing enilconazole (an antifungal agent that is also found in the topical medication Imaverol®) was also found to be very effective. This product is not approved for household use, but it is approved for use in catteries. It is also licensed as a topical treatment for dogs and horses in most of Europe and Canada.

Eliminating ringworm from the household or clinic environment can be difficult, because the fungus can be found anywhere that an infected animal (or person) sheds hair or skin cells.  Here are some guidelines for environmental disinfection of dermatophytes:

  • All bedding, brushes, combs, rugs, cages, etc. should be vacuumed, scrubbed, and washed with hot water, detergent, and 1:100 chlorine laundry bleach, or another effective disinfectant (see above). It is best to throw out any items that cannot be thoroughly disinfected.
  • Walls, floors, lamps, etc. should be scrubbed and cleaned in a similar manner.
  • Carpeted areas may be impossible to effectively decontaminate. If possible, remove the carpet and either wash in hot water and bleach, or discard it. Otherwise, frequent vacuuming with immediate disposal of the collection bag is necessary.
  • Vehicle interiors should be decontaminated as much as possible in a similar manner.
  • Curtains can be “dry-cleaned” at a professional cleaner.
  • Clean heating vents (from the house furnace) as well as possible. If the house is heated by hot air, change the furnace filter once weekly throughout the decontamination process.
  • Cleaning and disinfection of the environment should be repeated at least once every 4-6 weeks (the more often, the better) until all affected animals and people have eliminated the fungal infection.

Obviously, environmental clean-up for ringworm is quite an undertaking.  If infection can be identified early, lesions can potentially be kept covered and movement of pets can be restricted to reduce the extent and amount of environmental contamination.

Special thanks to Dr. Anthony Yu (one of the veterinary dermatologists at the Ontario Veterinary College) for providing much of the information in this post, as well at the photos.

Ringworm: skin fungus by any other name

Ringworm infection is not caused by a worm at all - it's actually a skin infection caused by certain kinds of fungus called dermatophytes. The scientific name for ringworm is dermatophytosis, or dermatomycosis. Some of the more common zoonotic species of dermatophytes found in animals include Microsporum canis, Trichophyton verrucosum, T. equinum, and T. mentagrophytes. There are also some dermatophytes that are primarily transmitted from person to person that are not carried by animals. These include the fungi that cause athlete's foot and jock itch.

Like many fungi, dermatophytes grow best in warm, moist environments, but they can grow almost anywhere on the body. They tend to grow around hairs and in the superficial layers of the skin, and the infection can be quite itchy. A ringworm skin lesion tends to spread out from one point on the skin, causing hairloss as it progresses, resulting in a bald patch (see picture right). The outside (most active) edge of the infection often appears as a red ring, from which "ringworm" gets its name.  The centre of the lesion may begin to heal, and the hair may start to grow back, even as the bald patch gets bigger.  It may take anywhere from a few days to a few weeks for visible lesions to develop after a person or animal has been infected. (Photo credit: A. Yu, Ontario Veterinary College)

Ringworm is quite contagious. The fungi are present in the large numbers on hair and skin cells that are shed by infected individuals. People or animals can be infected through contact with these infected hairs and skin cells, either directly on the affected person or animal (i.e. direct contact), or on things like clothing, blankets, hairbrushes etc. that have touched the affected skin (i.e. indirect contact).

Ringworm occurs all over the world, but no one knows exactly how common it is because there are so many different kinds of fungus that cause it, it's not reportable, and many cases probably go undiagnosed. Signs of ringworm in animals are often the same as in people, however not every animal that is infected with ringworm develops signs of infection. It has been estimated that ~90% of cats that are carrying dermatophytes do not show any signs of infection, but they can still transmit the fungus to other animals and people. (NB: this does NOT mean that ~90% of cats carry dermatophytes!)  Almost any animal can be infected by at least one dermatophyte or another - cats, dogs, rabbits, rodents... even horses and cattle!

  • Early identification of ringworm is important to reduce the risk of transmission to people and other animals. If your pet develops bald patches, particularly if they're itchy, it should be examined by your veterinarian to determine if a fungal infection may be present.
  • If you or anyone in your household develops an area of skin that appears infected (especially if it appears as a red "ring"), keep it covered with a piece of clothing or a bandage and see your doctor.
  • Most cases of ringworm can be treated with either topical (e.g. ointments) or oral anti-fungal medication.
  • Clean your pet's grooming supplies (e.g. brushes, combs) regularly.
  • Always wash your hands after handling your pet.

Watch for another Worms & Germs blog post about ringworm and how to clean up if you or your pet is infected, coming soon!  More information about ringworm and dermatophytes can be found on the CDC's Dermatophytes website.

Your mother was right! Wash your hands

You may notice a recurring theme in many of our posts and on virtually all of the information sheets on the Worms & Germs Resources page: an emphasis on handwashing. There is increasing emphasis on hand hygiene (i.e. hand washing and use of alcohol hand sanitizers) education in hospitals because the hands of healthcare workers are a major (if not the most important) means of disease transmission between patients. Despite hand hygiene being easy, cheap and effective, people rarely wash their hands as often as they should, and they often don't do it properly.

Most of the research about hand hygiene that has been published has focused on its use and impact in human hospitals, but this area is now also being studied more with regard to animals and veterinary medicine. A study published earlier this year in Veterinary Microbiology provided more evidence that hand hygiene is a critical infection control measure when dealing with animals. The study, coordinated by Dr. Maureen Anderson (of Worms&Germs fame) looked at MRSA carriage rate in veterinarians who work with horses. In addition to finding a high rate of MRSA carriage among these veterinarians (which was consistent with other reports indicating that equine vets are at higher than average risk for exposure to MRSA), the study looked at factors associated with MRSA carriage. Vets that reported routinely washing their hands between farms and those that reported washing their hands after contact with potentially infectious cases had a significantly lower rate of MRSA carriage. That should come as absolutely no surprise, but it's one more piece of evidence that we need to pay more attention to this routine infection control measure, in human hospitals, in veterinary environments and in households.

Remember, the 10 most important sources of infection are the fingers on your hands!

Click here for instructions on how to wash your hands properly.

Eastern equine encephalitis in Ontario

A horse in Ontario was recently diagnosed with Eastern Equine Encephalitis (EEE), a serious neurological disease caused by a virus of the same name, which is transmitted by mosquitoes.  The horse was from the North Durham region.  The last reported cases of EEE in Ontario were in 2004.  A few weeks ago, the Worms & Germs Blog talked about a large number of cases of EEE that have been reported in Florida this year.

Here are some of the key points to remember about EEE:

  • Like West Nile, EEE is a seasonal disease.  It is more common in warmer areas, especially some regions of the southeastern US.  It is rare in cooler climates, but occasionally EEE is found in horses in Ontario.
  • EEE is usually fatal in horses, and there is no effective treatment.
  • EEE can also occur in people, and can be fatal in some cases.
  • Infected horses cannot transmit the EEE virus to people, but if a horse gets EEE from the mosquitoes in the area, then people could also potentially be exposed to the virus by mosquitoes.
  • A vaccine for EEE is available for horses, but most horses in Ontario are not vaccinated for EEE because it is so rare.  Nonetheless, vaccination can be considered because the disease is so devastating when it occurs.
  • As for West Nile virus, avoiding mosquitoes - for both horses and people - is an important preventative measure for EEE.

For more information, see the Worms & Germs Blog post "Eastern Equine Encephalitis – Not Just For Horses", or the CDC's website on arboviral encephalitides.

Protecting your horse and yourself from West Nile virus

In Ontario, and many other regions, mid-August is the beginning of the high risk period for West Nile virus infection in people and animals such as horses. The Ontario Veterinary College has published an informational video on YouTube. This video has information about measures you can take to reduce the risk of West Nile virus exposure and disease, for both people and horses. Click on the image to watch the video.  More information about West Nile virus is also available in the blog post entitled West Nile virus in dogs and cats.

Eastern Equine Encephalitis - Not just for horses

Over 50 horses have died from Eastern Equine Encephalitis in Florida this year. The disease, caused by a virus of the same name, affects the brain, resulting in a broad range of clinical signs from behaviour changes to blindness to irregular gait. The disease is also sometimes called “sleeping sickness” because some horses may become severely depressed, with low head carriage and droopy eyes, ears and lips. Almost all horses that develop neurological signs from this infection die. Only 35 cases were reported in Florida in 2006 and 2007 combined.

There are actually three related equine encephalitis viruses – Eastern, Western and Venezuelan – which are called EEE, WEE and VEE for short. VEE is found in South and Central America and Mexico, and occasionally in the southern United States, but has never been reported as far north as Canada (VEE is a reportable disease in Canada). It is unique among the three diseases as the only one in which an infected horse will carry enough virus in its bloodstream to infect a mosquito, which could then pass the virus on to another animal. The EEE and WEE viruses, just like the West Nile virus, do not reach high enough levels in the bloodstream of horses to do this. The mosquitoes usually pick up the viruses from passerine birds, which do not become ill from the viruses (unlike West Nile virus in birds from the family Corvidae).

People can also be infected by EEE, WEE and VEE. About 10 fatal cases of EEE in people are reported in the United States every year. But horses cannot transmit EEE or WEE to humans, even if they’re bitten by the same mosquito. A higher number of cases in horses, however, may mean a higher number of mosquitoes that are carrying the virus. There is no vaccine for these viruses for humans, but there are vaccines available for EEE, WEE and VEE for horses.

In the end, EEE is just one more good reason to make sure you wear mosquito repellent when you’re enjoying the great outdoors during the summer. Visit the Health Canada website for safety tips on using personal insect repellents. EEE is very uncommon in Ontario, but horses that live in or travel to the southern United States should be vaccinated. Talk to your veterinarian about whether or not your horse should be vaccinated. Remember that fly control is also important for our equine companions (and also helps protect them against West Nile!).

Deadly Hendra virus resurfaces in Australia

A small outbreak of the potentially deadly Hendra virus was identified in a group of horses near Brisbane, Australia. This virus has caused periodic cases of illness and death in horses, and can be transmitted to people working closely with infected horses. In the latest outbreak, 3 horses have died, making this the worst outbreak since 1994 when 14 horses and 2 people died.  Now, a human case has been identified. This person works at a veterinary clinic that treated infected horses. This individual was admitted to hospital overnight but was discharged, so is presumably not very ill.

While Hendra virus (genus Henipavirus) is only found in Australia, it is a good reminder for everyone about the strange nature of some infectious diseases. The natural reservoir of the virus is the fruit bat. It is believed that horses become exposed when infected fruit bats give birth and contaminate horse pastures with uterine fluids. Horses develop respiratory disease ranging from mild to fatal. Human cases have been reported in people working closely with infected horses. A horse trainer and veterinarian's assistant died in the 1994 outbreak. Close contact is required for transmission to people.

Picture: Locations of previous Henipavirus outbreaks (red stars – Hendra virus; blue stars – Nipah virus) and distribution of Henipavirus flying fox reservoirs (red shading – Hendra virus; blue shading – Nipah virus)

It's very difficult to take specific measures to protect horses, people or other animals from sporadic, rare diseases such as Hendravirus infection. However, common sense infection control measures can reduce the risks associated with any animal contact.

  • Wash your hands after contact with any animal.
  • Avoid contact with sick animals - consider sick animals to be potentially infectious until proven otherwise.
  • Remember that  new animal diseases are regularly being identified, and that they might be able to infect people.
  • People that work in veterinary clinics must be diligent and use good infection control practices because they are at higher risk of exposure to various diseases.

Horses and MRSA

Many people in the horse world have heard the hype about methicillin-resistant Staphylococcus aureus (MRSA) in horses. MRSA can cause infection in horses, just like it can in people, dogs, cats and many other animals. It’s usually what we call an “opportunistic” pathogen, meaning it usually takes advantage of a person or an animal that is already sick or injured, like someone who’s in the hospital and has just had surgery. And because MRSA is resistant to many different antibiotics, the infection can be difficult to treat. The big concern with MRSA in recent years is that infections are now sometimes occurring in people who aren’t sick, and who don’t have wounds or incisions, which is where MRSA usually likes to move in. It’s very important to find out from the start if an infection is being caused by MRSA, so that it can be prevented from spreading to other people and animals, and so that it can (if necessary) be treated with the right kind of antibiotic.

Horses are a bit of a special case when it comes to animals and MRSA. When researchers look at the DNA of MRSA from a dog or a cat, it usually turns out to be one of the common human MRSA strains (usually called a “clone”) from the same area. This means that the dog or cat probably picked up the MRSA from a person somewhere.  When researchers look at the DNA of MRSA from horses, however, they often find a different clone, which seems to be more common in horses and people who work with horses than in people in general. A very similar situation has also been discovered in pigs. The worry is that this “horse MRSA clone” can survive in and be transmitted between horses better than the human MRSA clones. That means that in order to control MRSA, just controlling it in the people won't do the trick - we need to take steps to stop the spread of MRSA in horses specifically as well.

Here are some key points to help reduce the risk of your horse (and you!) getting MRSA

  • Always wash your hands with soap and water (or use an alcohol-based hand sanitizer) after handling a horse, and before handling another horse.
    • This is especially important if you have touched a horse’s nose, or any cuts or wounds that the horse may have.
    • Don’t go down the row of stalls in the barn and pet every horse on the nose! They love the attention, but this is a great way to spread MRSA if it’s there!
  • New horses coming into the barn, or animals coming back from a hospital, should be kept separate from all the other animals and only dealt with after all the other horses, for 3-4 weeks.
    • This is an important measure for controlling many infectious diseases, not just MRSA.
  • If your horse has a cut that looks infected, cover it with a bandage of some kind and contact your veterinarian. Your veterinarian can culture the wound to determine if it is an MRSA infection.

Horse visits hospital

Recently, a story about a man who brought a horse into a hospital to visit his father was widely reported. The horse apparently made it to the man’s room, which included a trip in an elevator. The son, who appeared intoxicated, was eventually asked to leave (and take the horse with him). Said a hospital spokesperson “We do have a pet visitation policy, but it does not include a horse”. Strangely, the horse that was brought to the hospital apparently wasn’t even the father’s horse (which supports suspicions of the son’s lack of sobriety).

There are guidelines about which animals are appropriate for hospital visits, although it shouldn’t take an expert to figure out that a horse is not an appropriate candidate. Kicks, bites, and trauma from being crushed or run over are among the most obvious concerns. Horses can also carry a variety of bacteria that are potentially dangerous, especially to people in hospitals. These include Salmonella and methicillin-resistant Staphylococcus aureus (MRSA). There also aren’t that many house-trained horses out there.

So, while I can easily see how someone in a hospital would like to see his or her horse, there’s no way this should even be considered.

Some closing thoughts
-    Would you like to ride in an elevator with a horse?
-    Would you like to be stuck in an elevator with a horse?
-    Do you think the horse was house trained?
-    Do you think any of the healthcare personnel washed their hands after touching the horse?

This isn't the first time a horse has been in hospital, and some even get invited. The picture is from a story in Veterinary Practice News that described a program where horses were brought into hospitals!

Equine Infectious Disease Information Sheets

Click on any of the highlighted links below for more information about these horse-related infectious disease topics. Topics that are not highlighted are in development and coming soon. New information will be added as it becomes available, so be sure to check this page regularly for the latest updates.

Bacteria Viruses Parasites Other
Clostridium difficile Rabies Bots Pleuropneumonia
Clostridial Myonecrosis Eastern Equine Encephalitis Equine Protozoal Myeloencephalitis (EPM) Neonatal Diarrhea
Strangles (Streptococcus equi) Equine Herpesvirus Cyathostomes
(Small Strongyles)
Needlestick Injuries
Methicillin-resistant Staph aureus (MRSA) Equine Influenza Large Strongyles Colostrum
Lawsonia West Nile Virus Tapeworms  
Rhodococcus equi Equine Infectious Anemia - Summary Pinworms  
Tetanus Equine Infectious Anemia - Full-length    
Botulism -
Botulism -
"Shaker Foals"

All information sheets found on this page can be freely downloaded, printed and distributed. The authors only request that this website (, previously is acknowledged as the source.  The downloadable files on this page can be opened with Adobe® Reader®.  To get the latest version of Adobe® Reader® for free, click here.

Research Posters

2012 International Clostridium difficile Symposium

2012 International Conference on Equine Infectious Diseases IX

2011 ASM-ESCMID Conference on Methicillin-resistant staphylococci in animals

2011 University of Guelph Centre for Public Health and Zoonoses Symposium

2011 Canadian Animal Health Laboratorians Conference

2011 Canadian Association of Clinical Microbiology and Infectious Diseases

Coming soon

  • 2011 American College of Veterinary Internal Medicine Forum, June
  • 2011 ASM-ESCMID conference on methicillin-resistant staphylococci in animals, Sept