Veterinarians in several states are determining the extent of a possible equine herpesvirus-1 (EHV-1) outbreak tied to cutting horses involved in a recent Odgen, Utah, championship show. Several animals that participated in the April 29-May 8 National Cutting Horse Association’s (NCHA) Western National Championship were diagnosed with the neurologic form of the illness, and at least two horses were euthanized when their conditions deteriorated.

Washington State University (WSU) officials placed the school’s Veterinary Teaching Hospital (VTH) under a voluntary quarantine effective May 13 after a horse admitted May 11 for orthopedic reasons tested positive for the virus.

"The hospitalization was relatively uneventful until Friday when the owner came to pick the horse up," said Debra C. Sellon, DVM, PhD, Dipl. ACVIM, a professor of equine medicine at WSU. "That morning, the horse had a very mild, low-grade fever of 101.5°F. The owner reported when he arrived that he’d heard rumors that there were herpes-positive horses at the national show and that this horse had been at the show."

Upon receiving the positive test results from the WSU diagnostic lab a few hours later, WSU officials put the hospital under quarantine, Sellon reported, meaning no horses are being admitted except for critical emergencies and horses currently at the hospital are remaining there throughout quarantine with their owners’ consent. She noted that the EHV-positive horse has since been discharged, however, because he’s shipping to an isolated farm where he will have no contact with nonexposed horses. The EHV-positive horse remains under the oversight of the Washington state veterinarian to ensure that there is no risk of spreading the virus to other horses