Two Confirmed Cases of Equine Herpes Myeloencephalopathy in Durham Region

Feb 17, 2017 Comments Off by Admin
February 17th 2017 – Veterinary Update Animal Health and Welfare Branch/Office of the Chief Veterinarian for Ontario, Ontario Ministry of Agriculture, Food and Rural Affairs
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.
February 16, 2017
Ontario cases of EHM and other equine neurological disease are listed at
Agricultural Information Contact Centre:  1-877-424-1300 E-mail:
Equine Disease Communication Center (EDCC)
CURRENT DISEASE OUTBREAKS. Updates on current disease outbreaks are listed here as they occur and will include the date listed, disease name, location and current status.
The OAHN Equine Network
Ontario Animal Health Network (OAHN) Equine Expert Network Equine Herpesvirus-1 Factsheet
Equine Herpesvirus-1- Be on the alert
• At least 70% of horses have been infected with EHV-1 as foals by their dams, and current vaccines and management practices cannot prevent this.
•  EHV-1 produces a latent infection, meaning these foals don’t show any clinical signs at the time, and the virus “hibernates” in the lymph nodes and in a group of nerve cells in the head where it remains inactive, or latent, establishing a carrier state that is life-long.
• Carrier horses do not show clinical signs and there is no laboratory test presently to detect them.
• Stress and suppression of the immune system causes carrier horses to start shedding the virus. Stressful situations such as shipping (especially over long  distance), overcrowding, mixing, illness, or pregnancy can cause the virus to become active and shed by the horse. It is thought that most outbreaks of EHV-1 are caused by reactivation from a carrier state.
• EHV-1 is transmitted by respiratory secretions. Horses become  infected by inhaling the virus shed by another horse, from nose- to-nose contact, or contact with infectious viral particles in the environment (tack, grooming supplies, stalls, trailers, clothing).
• Fever is an important clinical sign. Fever occurs days before the onset of neurologic signs are noticed.  It is, therefore, very important to take temperatures twice daily on all new horses arriving at your stable as a fever may be the only indication that an active virus is present.
•¨Neurologic disease is characterized by decreased coordination (ataxia) and hind limb weakness. After gaining access through the nose and entering the blood stream, the virus is delivered to the spinal cord.  Loss of balance and recumbency may then ensue.
• Only 10% of infected horses develop neurologic signs during an EHV-1 outbreak. The reason the virus attacks the vessels of the CNS in only certain horses is not completely known, although there is a strong relationship between the dominance of specific immune cells and the susceptibility to and recovery from EHM.
• After infected, the horse will shed the virus for 10-21 days.
• Quarantine new horses upon arrival for at least 2 weeks taking daily temperatures and making sure not to go back and forth between resident and quarantined horses.
• Report any abnormalities (fever or neurologic signs) to your veterinarian.
• Ensure your horses are vaccinated. Although vaccines exist to prevent respiratory disease and abortion due to EHV-1, at present there is no vaccine licensed to prevent the neurologic form of the disease.  Some veterinarians promote the use of the respiratory/abortion vaccines to reduce the shedding of the virus and limit the spread through the barn. Discuss this with your veterinarian and decide upon the best approach for you and your horse or stable.

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