Cancellation of equine events recommended after deadly virus detected in Flathead County

Following multiple confirmed cases of equine herpesvirus myeloencephalopathy in Flathead County, state officials recommend that area horse owners and event coordinators limit travel and cancel events through Feb. 6.

The recommendation from the Montana Department of Livestock is based on horses on three premises that attended gatherings at two or more event centers in the area that later became ill. Owing to poor prognoses, four horses have since been euthanized.

“In severe cases, we have no choice but to put the horses down,” said Montana State Veterinarian Martin Zakuski. “These animals are weak and off balance and, in the worst case scenario, they cannot get up. When it gets to that point, there really is no other choice.”

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 the virus beyond known travel history of the horses. If additional cases of the virus are detected, officials will extend the date.

An extremely common virus among horses with nine identified types, the U.S. Department of Agriculture estimates that nearly all horses in the U.S. have been infected with equine herpes virus by age 2, but the severity of symptoms, if any, depends on the type.

Equine herpesvirus myeloencephalopathy is a form of a potentially serious type of equine herpes virus, which can cause respiratory or neurologic disease in affected horses, but does not affect other animals or humans. The neurologic form, equine herpes myeloencephalopathy is often fatal to horses.

“We are not really sure how this strain got into the Flathead Valley and at this point we haven’t done genetic analysis to determine if this is a new strain that came in from an outside source or if it is a variant of an [equine herpes virus] strain that was already there,” Zaluski said. “This is something that circulates very much like the common cold and it is something that veterinarians vaccinate for. The virus itself is not uncommon. What is uncommon are these neurological manifestations that are so terrible for horses and their owners.”

There is currently no treatment that can cure equine herpes myeloencephalopathy, only procedures to reduce the symptoms of infected horses. There are vaccines against certain forms of the virus type, but Zaluski says they do not prevent neurological problems.

“You just hope that it doesn’t get bad. You can provide anti-inflammatory drugs or give fluids and pain meds, but there really is no treatment for this virus,” he said. “It might be worth it to keep any traveling horses away from the rest of your herd for the time being.”

To date, five cases of the neurologic form — three confirmed and two suspected — have been reported on three separate locations in the Flathead area. Four of the either confirmed or suspected cases have been euthanized due to the severity of disease. The fifth animal is exhibiting mild clinical signs and is under quarantine.

Exposed horses from the affected locations are also subject to quarantine for 21 days beyond the last date of potential exposure.

The state department reported 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.

According to Zaluski, the virus can be transmitted through direct horse-to-horse contact but is most commonly spread through dirty equipment such as horse tack, water troughs and tie ups.

“We think this virus has survived on surfaces for extended periods and that is how it is spreading — through the cross use of equipment and facilities,” he said. “That is what was behind our recommendation to cancel events in the area.”

WHILE THE Department of Livestock’s recommendation has brought about the cancellation of planned rodeo events at the Majestic Valley Arena Feb. 3-4, last weekend’s skijoring event in Columbia Falls took place after organizers consulted with the department.

“They contacted us and we made several recommendations about how to minimize risk. The fact that it was an outdoor event without a common corral for the horses was ideal. We made those recommendations before we learned of the third case, though. Whether or not that information would have led us to make a different decision, it is hard to say. We still believe the skijoring event was pretty low-risk,” Zaluski said. “That being said, the participants should probably still keep an eye on their animals. That is a standard recommendation in all cases, though. If you travel with horses, you should have some enhanced monitoring for them such as checking their temperature before every event and for several days after travel.”

Zaluski recommends that 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 the virus 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 should also be reported to the department and 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.

Reporter Jeremy Weber can be reached at jweber@dailyinterlake.com.