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West Nile Virus in Horses

The first case of West Nile Virus (WNV) in Alberta was reported in 2002, and while diagnosed cases are still rare infection from the virus poses a serious risk to horses and humans. Infected mosquitoes that bite susceptible hosts, such as horses, are responsible for spreading the virus. Crows, jays, magpies, and ravens are also susceptible to WNV, and dead birds of these species can be an indicator that an area is at risk.


The majority of horses infected with WNV will not show any visible symptoms and can fight off the infection naturally. However, when symptoms do manifest, they can be grave and numerous. Symptoms of WNV in horses include:

  • Listlessness or depression
  • Reduced appetite
  • Inability to swallow
  • Drooping lips
  • Fever
  • Impaired vision
  • Incoordination or weakness
  • Partial paralysis
  • Coma


These symptoms can be confused with rabies and should be investigated by a veterinarian immediately if they appear in a horse. Confirmed cases of WNV must be reported by the veterinarian to ensure the virus can be tracked should an outbreak occur. It should be noted there is no evidence that humans can get infected from contact with birds or horses. Humans contract WNV the same way that birds and horses contract it from being bitten by an infected mosquito.


Unfortunately there is currently no treatment available for WNV, but supportive therapy can help to reduce the severity of symptoms and consequently ease the horse’s suffering during recovery. Approximately 35% of horses die from infection or have to be euthanized due to complications.


Horses can be vaccinated against WNV.  Talk to your veterinarian to learn more about how you can keep your horses safe from the risk of WNV and other viruses. If you suspect that one or more of your horses may be infected with WNV, please contact your veterinarian immediately.



Alberta Agriculture and Forestry

Canadian Food Inspection Agency

CAHSS Equine Network


Additional Information:

Surveillance Information for Canadian Humans, Birds, and Horses