The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) has been notified of two confirmed cases of Equine Herpes Myeloencephalopathy (EHM), caused by equine herpes virus 1 (EHV-1). The horses from Durham Region were referred to the Ontario Veterinary College with neurological signs and are receiving treatment. Three other horses on the farm have tested positive for the mutated (neuropathogenic) strain of EHV-1 on nasal swabs, but are not demonstrating neurological signs at this time. The farm owner has voluntarily placed the premises under a self-imposed quarantine to reduce the risk of viral spread.
These are the first cases of EHM diagnosed in Ontario this year; however, cases of EHM have been diagnosed in California, Kentucky, Louisiana and Michigan since the beginning of the year. In 2015, there were three laboratory-confirmed cases of EHM in Ontario.
EHV-1 infection in horses can cause respiratory disease, abortion, neonatal foal death, and/or neurological disease. EHV-1 is not a federally reportable disease but is immediately notifiable by laboratories under the reporting regulation of the provincial Animal Health Act. Attending veterinarians suspicious of EHM should contact OMAFRA as soon as possible.
Because infected horses may show no clinical signs, but still shed the virus, the temperature of suspect animals should be monitored twice daily for 14 – 21 days and any abnormalities discussed with a veterinarian. Neurological signs, if they develop, may include loss or balance, hind-limb weakness, recumbency, difficulty urinating, decreased tail tone and depression. It is important that a veterinarian assess suspect cases of EHM since it can be difficult to distinguish this from other serious neurological diseases, such as rabies.
EHV-1 is easily spread by nose-to-nose or close contact with an infectious horse, by sharing contaminated equipment (bits, buckets, towels, etc.) or by the clothing, hands or equipment of people who recently had contact with an infectious horse. This highlights the need for routine biosecurity measures (including hand hygiene and basic cleaning and disinfection practices) to be in place at all times to prevent a disease outbreak. Special attention should be given to cleaning and disinfecting trailers.
Current EHV-1 vaccines may reduce viral shedding but are not protective against the neurological form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread.
The best method of disease control is disease prevention.