The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) received notice on Aug. 21 that two horses in that province tested positive for West Nile virus (WNV).

A 10-year-old gelding from Simcoe County was euthanized after developing severe neurologic signs and seizures. Meanwhile, a 25-year-old mare from Bruce County developed severe neurologic deficits in all four limbs as well as facial hyperesthesia (hypersensitivity to touch), but is recovering under veterinary medical supervision.

The OMAFRA said Ontario veterinarians should consider WNV as a differential diagnosis in horses with neurologic signs, and can identify positive cases through appropriate testing. West Nile is an immediately notifiable disease under both the federal Health of Animals Act and the provincial Animal Health Act.

West Nile Virus is endemic in Ontario and cases occur in the horse population at varying levels each year. Most equine cases occur between August and September, although cases can occur into October if environmental conditions permit the survival of the mosquito vector species