Colorado State, Washington State veterinary teaching hospitals restrict horse intakes; veterinary officials fear more equine herpes virus cases will emerge

National Report

— An outbreak of equine herpes virus-1 (EHV-1) traced to a recent equine event in Utah has put the horse community on alert across the United States and Canada.

Two cases of EHV-1 have been confirmed in Colorado. More cases are suspected in multiple other Western states. Of the two confirmed cases, both horses have been euthanized, according to the Colorado Department of Agriculture. At least six Colorado horses in four counties are showing symptoms of the disease and are under quarantine.

Both horses that were confirmed positive with EHV-1 in Colorado recently attended the National Cutting Horse Association’s Western National Championships in Ogden, Utah, between April 29 and May 8.

As result of the outbreak, Colorado State University’s (CSU) Veterinary Teaching Hospital announced May 16 it is immediately restricting all non-emergency equine and camelid veterinary appointments to prevent further exposure. Any potential infectious cases at CSU, including horses believed to have been exposed to EHV-1, would be placed in a separate isolation hospital that is physically removed from the main veterinary hospital. As a result of the outbreak, CSU canceled two riding clinics scheduled at the B.W. Pickett Equine Center in May, other events scheduled in June may be canceled as well.

Washington State University (WSU) restricted access to its Veterinary Teaching Hospital after another case of EHV-1 was confirmed in a horse that competed at the Utah show but was admitted for unrelated problems. WSU veterinary officials opted to shut down admissions for any equine or camelid patients at the teaching hospital for at least two weeks, except for critical emergency cases. No other horses at WSU’s teaching hospital have shown signs of EHV-1 infection, WSU veterinarians report.

The American Association of Equine Practitioners (AAEP) says the outbreak is affecting an unconfirmed number of horses across the United States and Canada.

The National Cutting Horse Association (NCHA), which hosted the Utah event that is believed to be the source of the outbreak, says it received credible, but unconfirmed, reports of cases not only in Colorado and Washington, but also in Oregon, Arizona, California and Western Canada. The Washington Department of Agriculture is also reporting cases in Idaho and Utah.

NCHA says its affiliates and other show producers in Montana, Oregon, Oklahoma, Texas, California, Wyoming, New Mexico, Washington and Nevada all have canceled shows scheduled for May 20 and 21.

Horse owners are being advised to notify veterinarians if they participated in the NCHA event, so their horses can be isolated and monitored for signs of EHV-1.

The virus spread through nasal secretions and horse-to-horse contact. Infected horse often present with a temperature above 102-F before clinical signs appear. The organism spreads quickly, says Dr. Leonard Eldridge, Washington's state veterinarian, and can present with neurological symptoms in affected horses. The incubation period for the virus is two to 14 days, but can be shed for up to 28 days. EHV-1-infected horses have high morbidity and mortality rates, Eldridge adds, and people can help spread the virus through contaminated hands, clothing, shoes and vehicles.