West Nile Virus (WNV) has been confirmed in the Regional Municipality of Waterloo, Ontario. On August 30, 2025, a 6 year old mixed breed mare presented to a referral hospital with anorexia, fever, diarrhea and neurologic signs (ataxia, sensitive to touch, cranial nerve signs). She responded to treatment and has returned home. Serum was positive on WNV IgM ELISA. The horse was not vaccinated against WNV.
This is the fourth confirmed case of equine WNV in Ontario this year. To see past and present WNV cases in Ontario go to: https://www.oahn.ca/resources/ontario-equine-disease-alerts/ and enter the disease surveillance portal.