On March 16, officials at the Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA) received notification of a confirmed case of equine herpesvirus myeloencephalopathy (EHM, resulting from equine herpesvirus or EHV). The affected horse resided at an equine facility in the regional municipality of Niagara.

The affected horse, a mature gelding of unknown breed and vaccination status, presented with clinical signs that consisted of difficulty urinating and severe incoordination in his hind limbs, progressing to recumbency (down and unable to rise). The horse was euthanized.

Farm staff have enacted enhanced biosecurity measures and movement restrictions under veterinary supervision.

This is Ontario’s fifth equine facility this year with confirmed equine herpesvirus-1 (EHV-1) that resulted in EHM.

EHV 101

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and equine herpesvirus myeloencephalitis (EHM, the neurologic form).

In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months) but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with EHM usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.

Herpesvirus is easily spread by nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or clothing, hands, or equipment of people who have recently had contact with an infectious horse. Routine biosecurity measures, including hygiene and basic cleaning and disinfection practices, should be in place at all times to help prevent disease spread.

Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.