West Nile Virus infection in horses, mules and donkeys is a provincially Notifiable Disease under the Reportable and Notifiable Diseases Regulation under the Animal Health Act.
This legislation requires anyone suspecting to knowing of a horse (or mule or donkey) infected with WNV to report that finding to the Office of the Chief Provincial Veterinarian at 780-427-3448 (Monday to Friday from 8:15 a.m. to 4:30 p.m.) and 1-800-524-0051 (after business hours).
The federal government has made WNV an Immediate Notifiable Disease under Canada’s Health of Animals Act.
This requires diagnostics laboratories to report the diagnosis of WNV to the Canadian Food Inspection Agency within 48 hours.
Most horses bitten by a mosquito infected with WNV will not develop clinical disease.
They develop an asymptomatic infection, eliminate the virus and continue performing as usual.
Symptoms in horses that do become sick can include listlessness, a change in demeanour resulting in them becoming less active and isolated, reduced appetite, inability to swallow, drooping lips, muscle twitching, a lack of co-ordination, weakness in the limbs, partial paralysis or inability to get up. A fever is not always present.
A veterinarian should examine suspected infected horses because these clinical signs are similar to those caused by Western Equine Encephalitis, Eastern Equine Encephalitis and Rabies.
Caution must be exercised when handling horses affected by nervous disorders, such as WNV, as animals may have a lack of co-ordination or tendency to fall leading to an increased possibility of handler injury.
There is no specific treatment for horses affected with WNV. Up to 30 per cent of horses showing clinical disease may die or have to be euthanized because of complications of the disease.
Some recovered horses may exhibit permanent neurological deficits.
Although the risk of disease in any individual horse is very low, the consequences for some affected horses can be severe.
Preventative measures should be discussed with your private veterinarian.
These measures include minimizing exposure to Culex taralis mosquitoes.
This species of mosquito breeds in small, warm still puddles of water.
Consideration can be given to providing screened housing and avoiding outdoor activities during peak times of mosquito feeding, such as dawn and dusk.
Using topical insect repellents and/or smudges may be useful.
Reduce potential mosquito breeding sites by eliminating standing water, cleaning water troughs weekly and keeping grass levels short around buildings.
Vaccines against WNV are licensed for use in horses in Canada and are available from veterinarians.
Horse owners should contact their veterinarian for information about the vaccines.