Ontario Horses at Two Boarding Facilities Contract EHM
Officials at the Ontario, Canada, Ministry of Agriculture and Food (OMAF) have confirmed two horses with neurologic equine herpesvirus (EHV), also known as equine herpesvirus myeloencephalopathy (EHM).

Both horses experienced onset of clinical signs on March 24; however, one was located in the municipality of Kawartha Lakes and one was located in Wellington County.

The Kawartha Lakes horse, a 17-year-old vaccinated gelding, was confirmed positive on March 25 after showing signs that consisted of ataxia (incoordination) and nasal discharge. He is reported as recovering. The number of exposed horses is unknown.

The Wellington County horse, a 19-year-old vaccinated pony gelding, was confirmed positive on March 26 after exhibiting signs that included ataxia and difficulty urinating. He is being treated at a referral hospital. No other horses on his property are showing clinical signs. Seven horses were exposed.

Veterinarians are working with the facilities to enact biosecurity measures and restrict animal movement.

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.