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
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.
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 TheHorse.com, 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.
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: http://coloradodisasterhelp.colostate.edu)
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: http://newshopper.sulekha.com/
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.
- 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.
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.
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.
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.
This week an article on TheHorse.com 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)
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 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: www.omafra.gov.on.ca)
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.
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.
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.
Despite relatively intensive efforts, no cause has been identified for the deaths of 22 horses ona Kooralbyn farm in Queensland, Australia. Readily identifiable causes have been ruled out, leaving two main theories:
As mentioned in an earlier post, one possibility is botulism It can be very hard to diagnose botulism in horses, and the disease is often presumptively diagnosed by ruling out all other reasonable options.
The other possibility is tick paralysis, which unfortunately is equally difficult to diagnose definitively. Certain types of ticks can cause progressive and severe paralysis which may look similar to botulism in some ways. Scrub ticks (the name typically used for Ixodes holocyclus) were noted on one of the first affected horses, but there's no information about whether all of the other horses had ticks too, and if so whether they were ticks that can cause paralysis. Kooralbyn is in a region where these paralysis ticks can be found and spring (e.g. now in Australia) tends to be the peak time for paralysis cases, so it's a reasonable consideration.
It's frustrating but far from unusual not to be able to make a solid diagnosis in outbreaks. Beyond the frustration factor, it's also a concern because it makes it hard to take precautions to prevent it from happening again.
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).
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.
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.
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.
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.
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.
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.
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.)
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: www.dailyclipart.net
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).
A large equine infectious anemia (EIA) outbreak has claimed the lives of 40 Arkansas horses. The outbreak has hopefully been contained to one farm in Johnson County. Two horses on the farm died from this viral disease, while 38 others were euthanized, presumably because they tested positive. Approximately 40 other horses are on the farm, and are presumably negative (at this time).
So far, the outbreak seems to be limited to this single farm. There is one neighbouring farm, which is being investigated to see if the insect-borne disease has spread. The affected farm does not show horses or 'sell any horses to any extent,' so hopefully the odds of the outbreak being contained are good.
A big question remains unanswered and is critical for determining whether this outbreak will be controlled: Where did the virus come from? Viruses don't just spontaneous pop out of nowhere (although sometimes it seems that way at first) - there had to be source of infection, and that source could have spread it elsewhere. With the large number of positive horses on this farm, it's concerning that the virus could have been introduced a while ago, and the longer the time frame, the harder it is to both track and control.
A somewhat confusing report in Lebanon's The Daily Star describes an outbreak of disease at Beirut's Hippodrome (racetrack) that has resulted in the deaths of 21 horses; 2 from disease and 19 that were euthanized as part of the outbreak response.
It's not specifically stated in the report, but the commentary about glanders, a highly infections disease caused by the bacterium Burkholderia mallei, suggests that glanders has been diagnosed or is strongly suspected. The two affected horses had been imported from Syria, which has been the source of other glanders outbreaks, and the disease is present in multiple countries in the region, so it's a likely cause. The reason for euthanasia of the 19 "healthy" (presumably exposed) horses is unclear. Hopefully it was done because they were identified as infected, however the report suggests that euthanasia preceded diagnosis.
Little information was provided about the response, beyond culling, with only a statement that "all relevant procedures had been taken." Additionally, a quarantine and testing requirement for horses entering Lebanon was announced by the mayor (presumably, a federal body has mandated this since I doubt the mayor of Beirut can set national importation policy). Measures for controlling glanders outbreaks are fairly well described and involve extensive investigation of horse contacts and movement, screening of potentially exposed horses, euthanasia of positive horses, quarantine of potentially exposed farms and use of stringent infection control practices. Hopefully a proper response is being undertaken here.
Beirut's mayor stated that there was "no possibility that the disease could be spread to humans," but that isn't consistent with glanders since this is a potentially serious disease in people as well. Two grooms that worked with the first two horses were tested and so far are negative and healthy. The likelihood of someone getting infected from an infected horse isn't great, but it's a very nasty disease so care must be taken and investigation of human contacts is important.
The Agriculture Ministry will apparently release its "all-clear" report in 6 months (assuming no more cases crop up). Let's hope that things truly are "all clear" in 6 months, with a subsequent report (presumably after official confirmation that the outbreak is over) thereafter. More details about the extent of testing and the results would be nice in the short term, to get a better understanding whether this is truly just a case of a couple of infected horses being imported with no transmission outside of the initial group, but political issues often limit the information flow in glanders outbreaks.
Image: Beirut Hippodrome (click for source)