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
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.
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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.
This Worms & Germs blog entry was originally posted on equIDblog on 17-Aug-11.
Natural disasters and pet diseases
After the devastation caused by Hurricane Katrina, there were numerous efforts to rescue animals left homeless or ownerless. As part of this, some animals were shipped far away, including large numbers to the Northeastern US and Canada. It was a time-consuming and expensive endeavour by very well-meaning people, but was accompanied by much controversy. Beyond the concerns about resources spent importing animals into areas where there is no shortage of strays and limited resources to care for them, there were infectious disease concerns. These concerns were real because of the potentially high incidence of disease, high rate of carriage of certain infectious agents and movement of dogs to regions where these diseases are rare or absent. Anytime you get population migration (be it human or animal) in response to a natural disaster, you have the risk of those migrants spreading diseases.
A study published earlier this year in the Journal of the American Veterinary Medical Association (Levy et al 2011) characterized some of these concerns. The researchers tested blood samples from 414 dogs and 56 cats that were transferred from the Gulf Coast region within four months of Hurricane Katrina. They tested the samples for a variety of infectious agents.
Among the highlights in dogs:
- Overall, 74% of dogs had "evidence of previous or current vector-borne infections." That's a pretty high number. Current versus previous is important, since the animals are only an infectious disease risk if currently infected. At least some of the testing was aimed at detecting infectious organisms (indicative of active infection), not just antibodies (which may indicate active or previous infection), so there was clear evidence that many dogs had active and potentially transmissible infections.
- Bartonella, Borrelia (Lyme disease), Ehrlichia and Babesia spp DNA were found rarely, in less than 2% of dogs. These organisms are spread by certain types of insects, and a concern with moving infected dogs is that it might allow for introduction of the disease into a new population if there are insects capable of transmitting these infectious agents in the new area. Fortunately, these weren't common.
- Canine influenza antibodies were found in less than 2% of dogs. This is a more important finding since canine flu is quite transmissible. While the virus is present in various parts of the US, it's distribution is pretty patchy. A dog infected with canine flu that comes into contact with other dogs in a new area could easily be the source of a local or regional outbreak.
- Dirofilaria immitis (heartworm) antigen was detected in 49% of dogs. This is a major concern and was one of the big causes of controversy in some regions. Dogs that are infected with heartworm and untreated are sources of infection. If bitten by a mosquito, heartworm can be transmitted to the mosquito, and then to other dogs (and less commonly cats, and very rarely humans). Heartworm is quite uncommon in many regions, and there were concerns that the transfer of these dogs could result in local increases in disease. Recommendations were developed to reduce the risk of heartworm dissemination, but given the high rate reported here, it's likely they were not widely followed.
- 56% of dogs had antibodies against West Nile virus. This is an interesting finding but not really relevant from a disease transmission standpoint. It likely reflects heavy mosquito exposure. West Nile virus is pretty innocuous in dogs and cats, and infected dogs and cats cannot pass on the virus to mosquiotoes or other animals.
- Dogs infected with heartworm were more likely to be infected with West Nile virus compared to those not infected with heartworm - presumably an indication of mosquito exposure.
The concerns are summed up nicely in the paper's conclusions: "Cats and dogs rescued from the disaster region had evidence of multiple infectious diseases. The dispersal of potentially infectious animals to other regions of North America where some infections were not typically found could have contributed to new geographic ranges for these organisms or to underdiagnosis in affected animals because of a low index of suspicion in regions with low disease prevalence."
I'm not saying don't rescue dogs and cats during disasters. Personally, I have to question the wisdom of putting the time, effort and resources into shipping animals around the continent when pretty much every jurisdiction already has their fill of animals in need of care, but people have different opinions. What common sense and this study should tell us is that we need to think about the infectious disease implications of mass animal movement, particularly marginalized animals with questionable or unknown disease status. Any large scale movement of animals needs to be accompanied by careful assessment of possible risks, and measures to make sure animals are properly tested and treated so that they don't pose an undue risk to the regions where they end up.
Image: Hurricane Katrina on August 28, 2005 (NASA)(source: http://en.wikipedia.org)
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...
This Worms & Germs entry was originally posted on our sister site, equIDblog, on 11-Mar-10.
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.
Dogs and dead birds
As the owner of a dog that loves to roll in (and eat) anything she finds, I certainly understand the questions that I get about risks to dogs from dead birds. Eating a dead bird is certainly not an appealing thought to us, but overall, the risks to a dog are pretty low. The greatest potential problem is likely gastroenteritis, often referred to as ‘garbage-gut’, which typically causes diarrhea (with or without vomiting) after "dietary indiscretion" (i.e. a dog eating things it shouldn't have). Another concern is Salmonella. Some birds carry Salmonella in their intestinal tracts and dogs could become infected from eating them. This is a bigger problem in cats that hunt birds - salmonellosis in outdoor cats is also referred to as songbird fever. West Nile virus can cause death in birds, especially species such as bluejays and crows, which may then be found by your dog. The risk of transmission of West Nile virus to dogs from eating dead birds is presumably very low. Further, this disease is very rare in dogs and they appear to be quite resistant to the virus. - Try to prevent your pet from eating/touching dead birds.
- If your pet develops diarrhea after eating a dead bird, it is probably not a health concern for anyone else but Salmonella infection is possible, so consider taking your dog to the veterinarian. This is especially important if the dog appears sick (i.e. besides vomiting and diarrhea, the dog also is not acting like itself) or if there are people in the household that are at higher risk for getting sick from bugs like Salmonella (i.e. infants, people with weakened immune systems). All diarrhea should be considered potentially infectious to other animals and people. Extra care should be taken around affected pets and their stool, including extra attention to hand washing, and disinfecting the site of any "accidents" that occur in the house.
- In some areas where bird testing is performed for West Nile virus or avian influenza surveillance, public health personnel will collect dead birds. Contact your public health department if you are unsure what is done in your region.
- Do not touch dead birds with bare hands.
- Use heavy-duty, leak-proof gloves to place the bird in a leak-proof plastic bag. Alternatively, fold two bags over your hand and use the bag to cover your hand when picking up the bird (like people do when poop-scooping), or use a shovel to place the bird in a bag.
- Double bag the bird.
- If the bird is not being collected for testing, contact your local waste management agency regarding disposal instructions.
- Always wash your hands with soap and water as soon as you're done.
West Nile virus in dogs and cats
One thing that has become very clear around my house the past few days is that mosquito season has arrived. Along with the annoyance, buzzing and itching, mosquitoes are of concern because they can transmit various viruses, including West Nile virus. While West Nile season tends to be later in the summer and fall in most regions, West Nile virus awareness and mosquito bite avoidance should be considered whenever mosquitoes are around.
Most of the attention about West Nile virus has been paid to humans, horses and birds, because of widespread illness and death in those species. Dogs and cats can certainly be exposed to West Nile virus if they are bitten by an infected mosquito; just like people and other animals. However, there are very few reports of West Nile virus infection in dogs, and even fewer in cats. Most dogs and cats that are infected do not develop signs of disease and simply develop antibodies against the virus.
Even if dogs or cats develop West Nile virus infection, there is no risk of transmission to other animals or human. This is because there is never a large enough amount of virus in the blood of these animals for a mosquito to pick it up and transmit it to another animal or person. The virus also can't be transmitted by direct contact with an infected dog or cat. West Nile virus is not found in saliva, so it is also unlikely to be transmitted by an animal (instead of an insect) bite.
There is no reason to be concerned about transmission of West Nile virus from your pets. If you live an area where West Nile virus is present, you should take precautions to avoid mosquito bites, such as avoiding mosquito-dense areas, wearing insect repellent with DEET, wearing long pants, long sleeves and socks when outside, avoiding peak mosquito hours (dusk and dawn) and eliminating any areas of standing water where mosquitoes can breed.
