Since the last major outbreak of West Nile Virus seen in Ontario in 2002, the majority of horse owners have chosen to protect their horses against this potentially fatal disease through annual vaccinations. This lead to a huge decline in the number of positive West Nile cases reported in the province for the following few years. Surveillance of the mosquito populations in Ontario throughout this time period has shown that although the number of horse cases reported has been low, West Nile Virus is still prevalent – and a potential risk for your horse.

This past summer has seen a rise in the number of positive West Nile cases reported here in Ontario. At last update, OMAFRA has reported 6 positive horses spread across the following cities: Chatham-Kent, Haldimand, Hamilton-Wentworth, Simcoe, Waterloo and West Nipissing. (http://www.omafra.gov.on.ca/english/livestock/horses/westnile.htm)

Although they were not diagnosed, two suspected cases of West Nile were seen in our practice area late this summer – leading us to believe that there are mosquitoes in the area carrying a high burden of the virus.

Symptoms of West Nile Virus in horses can consist of some or all of the following:




-Loss of appetite




-Partial to full paralysis



Many horses will recover from the acute phase of the disease, but retain neurological deficits that can prevent them from continuing with their previous athletic endeavours, and may affect their quality of life.

The simplest thing you can do to protect your horse from this disease is to protect them, with annual vaccination. Horses that have not been vaccinated previously will need an initial vaccine, followed by a booster at 3-4 weeks, but otherwise once-yearly will give sufficient protection.


Horses vaccinated at this time of the year will have full immunity to West Nile Virus for 12 months, and can stay on a fall-vaccination schedule for years to come. Sometimes this is even preferable to giving all vaccines together at one time of year, as it may reduce the possibility for vaccine reactions.

Please contact us to arrange vaccination for your horses – it is much easier to prevent this disease than to treat it! 519-229-8911