Equine herpes myeloencephalopathy (EHM) has been confirmed in Grey County, Ontario. On February 17, 2024, a four year old pregnant Warmblood mare was admitted to a referral hospital for treatment of acute neurologic signs (4/5 ataxia, head tilt and cranial nerve deficits). Nasal swab and blood samples were positive for equine herpes virus 1 (EHV-1) by PCR on February 21, 2024. The horse is recovering. There were four other suspected cases, three of which have been euthanized.

The farm owner is working with their veterinarian to implement voluntary animal movement restrictions and infection control measures. This mare was one of 23 horses bought at a sale in Illinois at the beginning of February. The horses were transported to a holding facility in Indiana prior to shipping to Ontario and delivered to farms in Grey County and surrounding areas. So far, the 5 confirmed/suspect horses were horses that arrived on these trailers. Veterinarians in the area are working with owners to manage the outbreak.

EHV-1 infection is immediately notifiable by laboratories to the Office of the Chief Veterinarian for Ontario under the Animal Health Act, 2009. Attending veterinarians concerned about potential cases of EHV-1 infection may contact an OMAFRA veterinarian through the Agricultural Information Contact Centre at 1-877-424-1300.