HELENA - The Montana Department of Livestock (DOL) is recommending that horse owners and event coordinators limit travel and cancel events that bring horses from multiple sources following multiple confirmed cases of equine herpesvirus myeloencephalopathy (EHM) in Flathead County.
The DOL recommends these actions take place through Feb. 6, 2023. The recommendation is based on the involvement of horses on three premises that attended events at two or more event centers in the area. Several horses have been euthanized.
The date of the department's recommendation spans 14 days which is one full incubation period (time from exposure to the development of clinical signs) of EHV-1 beyond the known travel history of involved horses.
DOL officials note if additional cases of EHV-1 are detected, this date will be extended.
According to DOL, five cases of EHV-1/EHM (three confirmed and two suspected) have been reported on three separate premises to date. Four of the confirmed and suspected cases have been euthanized due to the severity of the disease. The fifth animal is exhibiting mild clinical signs and is under quarantine.
Exposed horses from the affected premises are also subject to quarantine for 21 days beyond the last date of potential exposure.
The department reports that several of the affected horses had no travel history, but herd mates — who remain without symptoms — attended events where they were exposed and therefore, likely contributed to disease spread at their home locations and other equine events.
“Disease spread in apparently healthy horses is an important consideration in our recommendation for the cancellation of equine events,” said Montana State Veterinarian, Dr. Martin Zaluski.
Horse owners who have attended events in the Flathead Valley in recent weeks should monitor their animals for fever (temperature greater than 101.5˚ F) or development of any neurologic signs for two weeks after their last travel.
Neurologic signs can include incoordination, difficulty walking, weakness, paralysis, inability to stand, poor tail tone, and difficulty urinating. Horses infected with EHV-1 may also have respiratory signs such as cough, nasal discharge, lethargy, and decreased appetite.
Horse owners concerned about the health of their horses should contact their local veterinarian. Suspected cases of EHV-1/EHM should also be reported to the department. The Montana Department of Livestock can be reached at 406) 444-7323 or via email at firstname.lastname@example.org.
EHV-1 is a potentially serious disease of horses that can cause respiratory or neurologic disease in affected animals. The neurologic form of the disease — equine herpes myeloencephalopathy — is often fatal.
The disease is primarily spread through aerosol transmission by inhalation of droplets from coughing and snorting. Additionally, the virus can be viable for several weeks in the environment and spread indirectly between horses. Common water sources, feeders, tie-outs, and shared equipment and tack can all contribute to spread.
Additionally, people can carry the virus between animals, typically through inadequate washing of hands or equipment. Horse owners should work with their local veterinarians on biosecurity recommendations to help reduce disease spread.
General recommendations for equine travel include:
- Keep any horses exhibiting signs of disease, including fever, at home.
- Avoid shared water sources, equipment, tie-out locations, and trailering.
- Consider isolating horses that travel off-premises away from their resident population of horses.
- Horses that have attended events should be monitored for 14 days beyond their last event.
- If an animal develops a fever, shows signs of respiratory illness, or neurologic disease, please isolate the animal and contact your local veterinarian.