West Nile virus is becoming a more serious issue in horses — rates are rising in Alberta and a third of the horses which become infected will die.
But there is a way to protect your horses, said veterinarian Melissa Smith of West Wind Veterinary Hospital in Sherwood Park.
“There are vaccines available for West Nile,” she said. “It is one that we consider a core vaccination for horses. We know that any horse can be exposed and it is a disease that is seen in our area and it can have severe consequences such as death.”
West Nile is mosquito borne, and horses can contract the virus from just one mosquito bite. Every horse is at risk of equal exposure, said Smith.
“It is Canada-wide and Alberta has the highest number of cases,” she said.
In 2017, there were only 54 cases in Canada, with 11 cases in Alberta. But last year the number of confirmed cases nationally jumped to 123 with 72 cases — nearly three-fifths — in Alberta. Saskatchewan had 32 cases and Ontario was a distant third at 11, with Manitoba, B.C., and Quebec accounting for the remaining handful.
“There will be some unreported cases as well since some don’t get diagnosed and some die. It’s likely higher. That’s something to consider as well,” said Smith, who so far, hasn’t seen a case of West Nile at her clinic.
It takes about two weeks for a horse to show symptoms of the disease after being bitten by a virus-carrying mosquito.
Many horses will not show any signs. Those that do often have flu-like symptoms, such as fever and lethargy. Some horses will show neurological signs such as being unco-ordinated in their hind legs and stumbling. Others can suffer a seizure or become comatose, but this is less common.
“Some report that they are hypersensitive to touch, but this is also less common,” said Smith.
It’s important to book an appointment with the veterinarian if a horse is acting in an off manner, because early detection of the disease can help to prevent a fatal outcome.
“You should have an exam done to pinpoint where the abnormality is coming from because it could be something that is very mild in some horses and very severe in others,” she said.
If a veterinarian suspects West Nile, he or she needs to confirm it with a lab (with positive cases reported to the Canadian Food Inspection Agency, which tracks disease surveillance).
West Nile is not transmissible from horse to horse, and a horse cannot spread it to a human.
Unfortunately, there is no specific treatment or drugs available for West Nile. The only option is supportive care. Smith said a horse infected with West Nile would likely need to be hospitalized. The main thing that can be done is to try and prevent the disease from taking hold in the first place. And that’s why vaccines are so important. They are available as a single vaccine or in combination with vaccines for other common horse diseases.
Smith said that her clinic recommends West Nile vaccines for all horses and that the majority of horse owners that she works with are taking that advice. The initial vaccination requires two injections a few weeks apart and then a yearly booster.
“That coincides with other core vaccines like tetanus that come in a combination,” said Smith, adding her clinic uses a combination that provides protection for eastern and western equine encephalitis, tetanus, and West Nile.
Ideally, it’s best to have a mare vaccinated since a foal is susceptible on its first day of life. However, a foal born to a vaccinated mare receives antibodies from drinking its mother’s colostrum. The young horse should later start its own vaccination schedule.
To reduce the presence of mosquitoes around horses, producers can use fly sheets, sprays, or a burn pit that produces smoke to reduce the presence of mosquitoes. Smith recommends minimizing free-standing water around the farmyard.
“If the horses are in a wooded or marshy area, they may be in an increased risk,” she said. “All it takes is one mosquito. You can try to reduce your mosquito burden, but all it takes is one.”