EHV-1 Outbreak: At Least Eight New Cases Reported

Animal health officials today confirmed several new cases of neurologic equine herpesvirus-1 (EHV-1) across the western United States and Canada. Now, two weeks after reports of EHV-1 positive horses first emerged following the recent National Cutting Horse Association's (NCHA) Western Regional Championship competition in Utah, the case count stands at more than 55.

Although it's not transmissible to humans, EHV-1 is highly contagious among horses and camelids, and is generally passed from horse to horse via aerosol transmission (when affected animals sneeze/cough) and contact with nasal secretions. The disease can cause a variety of ailments in equines, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and myeloencephalopathy (EHM, the neurologic form). Myeloencephalopathy is characterized by fever, ataxia (incoordination), weakness or paralysis of the hind limbs, and incontinence.

New Information

At press time (5:00 p.m. EDT), state officials had reported the following updates:

New Mexico--In a memo to veterinarians, horse owners, and equine event coordinators released yesterday, New Mexico State Veterinarian David Fly, DVM, indicated that three facilities within the state are currently under quarantine due to the neurologic form of EHV-1.

"One horse has died, two horses are clinically ill, and one horse has recovered," he said in the memo. "The last case in New Mexico was reported on May 20, 2011. All other horses on these quarantined premises are under close observation and are being monitored by their farm veterinarians.

"It is recommended that major or large equine events not be conducted for the next 10 days," he added.

No further information about the affected horses in New Mexico was available at press time.

Nevada--Two additional cases of EHV-1 were confirmed in Nevada today, according to a press release from the state's Department of Agriculture; there are now a total of three EHV-1 positive horses in Nevada. The two new cases are located in Washoe County (in the northwest part of the state); these animals, which have displayed neurologic signs, were exposed to two horses that attended the NCHA competition in Utah. The two animals that attended the competition have not shown any signs of illness, the statement said. The first horse confirmed EHV-1 positive in the state (reported yesterday) is located in Elko County in Northeast Nevada.

Idaho--A statement released today by the Idaho Department of Agriculture indicated five additional horses located on a quarantined premises tested positive for EHV-1, bringing the state's total to six.

"Two of these horses had attended the NCHA cutting in Ogden, Utah and three were stablemates at the same Idaho facility," the statement read. "All of these horses are under veterinary care and will remain under quarantine for a minimum of 28 days from this point. The horse owners are following appropriate biosecurity measures to prevent the spread of the disease outside of the facility."

Three of the EHV-1 positive horses have displayed neurologic signs and three remain only febrile (feverish), the statement said. Officials did not indicate which horses were affected with neurologic signs.

Alberta--Gerald Hauer, DVM, Alberta's chief provincial veterinarian, reported an additional EHV-1 case confirmation today, however the horse appears healthy. He said that the horse was exposed to the virus and tested positive for neurologic EHV-1 via lab test. The new confirmed case brings Alberta's total to five (three of which displayed respiratory signs and two exhibiting no signs of illness).

Washington--Debra C. Sellon, DVM, PhD, Dipl. ACVIM, a professor of equine medicine at Washington State University (WSU), confirmed today that no new cases of EHV-1 were diagnosed at the school's Veterinary Teaching Hospital. The state's Department of Agriculture's website also indicated that no new cases were reported, leaving the number of confirmed cases in Washington at seven.

Three of the seven EHV-1 positive horses have only displayed signs of a fever. The clinical signs associated with the other positive cases were not reported.

No New Updates

At press time, the following states and province had not reported any updated information:

  • Arizona--1 positive (euthanized with neurologic signs)
  • British Columbia--0 positives
  • California--18 positives (one neurologic horse euthanized; seven others displayed neurologic signs, and the remainder only were febrile or showed no clinical signs)
  • Colorado--9 positives (two euthanized with neurologic signs; clinical signs of surviving horses not reported)
  • Montana--0 positives
  • Nebraska--0 positives
  • North Dakota--0 positives
  • Oregon--3 positives (clinical signs not reported; an additional horse euthanized after developing neurologic signs)
  • Utah--7 positives (one euthanized after becoming recumbent, or unable to rise; clinical signs of surviving horses were not reported)
  • Wyoming--0 positives

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