EHV-1 Outbreak: New Cases and Travel Requirements

Two states and one province have reported new confirmed equine herpesvirus-1 (EHV-1) cases within their borders 13 days after veterinarians began tracking an outbreak of the virus, which sometimes causes neurologic signs. The National Cutting Horse Association's (NCHA) Western Regional Championship (held April 29-May8 in Ogden, Utah) is believed to be the point of origin for the outbreak, and animal health officials are still monitoring horses exposed at the competition closely.

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 Cases:

At press time (5:00 p.m. EDT), the following states had reported new confirmed cases of EHV-1:

Nevada--A press release issued late Tuesday (May 24) by the Nevada Department of Agriculture indicated that state authorities received the first report of a confirmed case of EHV-1. The release stated that the horse--which is located in Elko County, in the northeast part of the state--attended the NCHA in Utah.

"The horse contracted the mild form of the disease and is expected to make a full recovery," the release read.

It is not known whether the sick horse displayed neurologic signs.

Alberta--Gerald Hauer, DVM, chief provincial veterinarian in Alberta, reported today that one additional case of EHV-1 was confirmed in the province, bringing the total number of horses with EHV-1 in Alberta to four. He said that one horse is confirmed to have the neurologic form of the virus and three have only shown respiratory clinical signs. Tests results are pending for one additional horse displaying neurologic signs, he added.

Washington--Debra C. Sellon, DVM, PhD, Dipl. ACVIM, a professor of equine medicine at Washington State University (WSU), confirmed today that a third horse at the WSU Veterinary Teaching Hospital tested positive for EHV-1. Sellon said that the horse is only febrile (showing a fever) and has not displayed any neurologic signs. She added that the three horses most recently confirmed positive at WSU were all likely exposed to the index case (the first EHV-1 confirmed case at WSU) that was discharged from the hospital on May 13. The most recent confirmed case brings Washington's total to seven.

Oregon--The number of confirmed cases in Oregon remains at three (none of which have displayed clinical signs), however a fourth horse has been euthanized after developing neurologic signs, according to the state's Department of Agriculture. Further information on that horse was unavailable at press time (i.e., the horse's cause of illness has not been confirmed).

No Reported Change:

At press time, the following states and provinces had not reported any new confirmed cases, leaving their confirmed positive case counts at:

  • Arizona--1 positive (euthanized with neurologic signs)
  • British Columbia--0 positives
  • California--18 positives (one euthanized with neurologic signs; seven displayed neurologic signs, while 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)
  • Idaho--1 positive (euthanized with neurologic signs)
  • Montana--0 positives
  • Nebraska--0 positives
  • New Mexico--1 positive (euthanized with 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

New Travel Requirements

North Dakota--Effective immediately, a health certificate is now required for all horses entering North Dakota, according to an order handed down by the state Board of Animal Health on May 24. Previously, a health certificate was not required for horses remaining in the state seven days or less. A current negative Coggins test is also required for entry into the state.

Washington--The state of Washington also will require all horses entering the state to hold a health certificate, according to a letter to horse owners from State Veterinarian Leonard Eldridge, DVM, dated May 23. Officials put the previous exemption ("Horses traveling into Washington State with their Oregon or Idaho owners in private conveyance for round-trip visits of not more than four days duration for purposes other than breeding are exempt from the certificate of veterinary inspection.") on hold in response to the EHV-1 outbreak. A current negative Coggins test is also required for entry into the state.

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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