Cases of West Nile Virus in Horses Increase in Alberta

According to a joint memo from Alberta's Chief Provincial Veterinarian and the University of Calgary Faculty of Veterinary Medicine, Alberta has recently seen an increase in neurologic cases of West Nile Virus (WNV) in horses.

As of October 3, 2023 there have been 18 laboratory confirmed positive cases reported. This number is likely an underestimation, as many horses go untested or may show mild signs not immediately recognized as WNV.

Most confirmed WNV cases occurred in horses that were either unvaccinated or had an unknown vaccination history. WNV can be fatal for horses who contract the disease, so vaccinating for WNV is considered part of the veterinary recommended core vaccination protocol.

WNV is a mosquito-borne disease that can cause inflammation of the brain and spinal cord, resulting in death in about one third of cases that show clinical signs of infection. Unfortunately, there is no specific treatment for WNV in Canada and infected horses often require intensive supportive care, including anti-inflammatories, pain medications, and intravenous fluids. Approximately 40 per cent of horses that survive infection may have ongoing neurological issues, such as gait and behavioral abnormalities six months post-diagnosis.

While WNV is not contagious between horses, it can closely resemble equine herpes virus-1 (EHV-1), a very contagious virus requiring isolation of horses to prevent the disease from spreading. Therefore, isolating a horse showing neurological signs and testing for both WNV and EHV-1 is strongly recommended.

WNV is here to stay in Alberta, so planning an annual vaccination for your horse in the spring is recommended to reduce the spread of the disease.

More information for horse owners:

Equine Disease Communication Center (EDCC) with disease alerts from Canada and the USA

EDCC WNV Owner Information with links to factsheets

Canadian Animal Health Surveillance System (CAHSS) Equine Network 

Equine Disease Dashboard (CAHSS) with up to date information on WNV cases reported in Canada by location

American Association of Equine Practitioners Core Vaccination Guidelines including WNV recommendations for various life stages (adult, foal, pregnant, etc.)

Invasive mosquitos in Calgary and Edmonton, University of Calgary Faculty of Veterinary Medicine research