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), according to a Equine Disease Communication Center (EDCC) alert.
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.
Equine Herpes Virus (EHV-1) infection in horses can cause respiratory disease, abortion in mares, neonatal foal death and neurological disease. The neurological form of the disease is known as Equine Herpes Myeloencephalopathy (EHM) and may be caused by damage to blood vessels of the brain and spinal cord associated with EHV-1 infection. EHM is most often due to the neuropathogenic strain of EHV-1, but may occasionally be caused by the non-neuropathogenic strain of the virus.
EHV-1 is easily spread and typically has an incubation period between 2-10 days. Respiratory shedding of the virus generally occurs for 7-10 days, but may persist longer in infected horses. For this reason, a twenty-one day isolation period of confirmed positive EHM cases is recommended along with stringent biosecurity protocols. Similar to herpes viruses in other species, the latent form of EHV-1 can reactivate at a later date, but generally with a low viral load posing a low risk of infecting other horses. Humans are not at risk of contracting the virus, however humans can act as an indirect mode of transmission.
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