Multiple Western States Affected by EHV-1 Outbreak

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.

"Right now, we're monitoring the horses' and the camelids' (currently at the hospital) temperatures twice a day," Sellon said. "If any horse has a temperature above 101°F, we're doing nasal swabs and testing. The plan right now is that we will maintain the quarantine for two weeks from the time the first infected horse left the hospital. If there is another positive, we have to reset."

She added that no other EHV-1 positive horses have been identified at the VTH.

The Colorado Department of Agriculture (CDA) issued a statement late on May 13 indicating two farms in Weld County, located in north central Colorado, were placed under quarantine. One horse that displayed severe clinical signs was confirmed as EHV-1 positive and was euthanized May 11, and another horse was quarantined after veterinarians diagnosed the animal as having of EHV-1. Both horses had recently returned from the Western National Championships before falling ill.

Additionally, a horse at a cutting show in Bakersfield, Calif., hosted by the Kern Country Cutting Horse Association (KCCHA), was euthanized the morning of May 13 after displaying clinical signs consistent with the neurologic form of EHV-1. According to Peggy Biller, president of the KCCHA, the horse was taken to the California Animal Health and Food Safety Laboratory at the University of California, Davis, (UC Davis) Veterinary Medicine Teaching and Research Center, in Tulare, for necropsy.

"I have not gotten a confirmed diagnosis on it yet," Biller said.

Biller added that one additional exposed horse was taken to the UC Davis William R. Pritchard Veterinary Teaching Hospital for observation; she said the horse "is still doing well." Both horses had recently returned from the NCHA competition in Utah.

The NCHA has canceled two competitions scheduled for May 14-28 in Tulsa, Okla., as a precautionary measure. A statement on the organization's website indicated that while no horses in the Tulsa area have displayed signs of EHV-1, the NCHA Board of Directors elected to cancel the show until the extent of the outbreak has been determined.

Equine herpesvirus is highly contagious and can cause a variety of ailments in horses, including rhinopneumonitis (a respiratory disease mostly of young horses), abortion in broodmares, and myeloencephalopathy (evident in the neurologic form). The virus is not transmissible to humans. Clinical signs of the neurologic EHV-1 form include fever, ataxia (incoordination), weakness or paralysis of the hind limbs, and incontinence.

TheHorse.com will continue to provide updates on the EHV-1 outbreak as more information becomes available.

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Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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