The season has arrived. Right on schedule, the first case of West Nile virus (WNV) infection in an Ontario horse has been identified, prompting an advisory from the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). The affected horse was from Sudbury, Ontario, and was euthanized because of progressive and severe neurological disease. It had not been vaccinated against WNV.
Presumably, this is just the start of at least a few cases in the province, although there was only one reported case last year. Vaccination of horses can provide protection against the disease, but it takes time to respond to a vaccine, so vaccinating now may not provide protection for at least a few weeks. This is especially true for horses that have never been vaccinated before because they need two doses of vaccine about 3 weeks apart (called a “primary series”) to be protected. But, remember that no vaccine is 100% protective, so it’s also important to avoid the mosquitoes that transmit the virus by taking precautions like staying inside at dusk and dawn and using insect repellant – precautions that apply to horses and their owners alike.