EHV-1 Outbreak: Confirmed Cases Still Being Reported

Despite a slow in the rate at which confirmed cases of equine herpesvirus-1 (EHV-1) associated with the current outbreak are being reported, new horses are still testing positive for the disease. Believed to stem from a national cutting horse competition held in early May in Utah, the outbreak has now been active for more than a month since the first cases were confirmed in mid-May.

Although it's not transmissible to humans, EHV-1 is highly contagious among horses and camelids, and it 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.

Many animal health officials believe the outbreak is winding down, and several of the horses diagnosed early have been treated and released from quarantine.

New Cases

Alberta--Twelve cases of EHV-1 have now been confirmed in Alberta, according to a statement released by the Office of the Chief Provincial Veterinarian on June 13. Three of the confirmed cases have displayed neurologic signs and four have exhibited respiratory signs or fevers, and five have been asymptomatic. In addition to the confirmed cases, four suspected cases have also been reported (three have displayed neurologic signs and one displayed respiratory signs.

"Cases have been confirmed in Southern Alberta, in the Calgary area, in the Edmonton area and in the Peace Country, and all are in the cutting horse industry," the statement read. "Horses that are confirmed positive or are suspects are being voluntarily isolated to reduce the chance of spreading the disease."

Montana--The first confirmed case of EHV-1 was reported in Montana, according to a press release issued June 13 from the state's Department of Agriculture.

"We have a nonclinical EHV-1 positive case associated with the National Cutting Horse Association (NCHA) Western National Championships in Ogden, Utah, April 30-May 8, 2011," Marty Zaluski, DVM, Montana state veterinarian, said in the press release. "Fortunately, this horse not only remains healthy, but has been separated from other horses since returning from Ogden."

The EHV-1-positive horse is located in Gallatin County.

Washington--An additional case of EHV-1 was confirmed in Washington, according to a statement released June 15 on the state's Department of Agriculture website. The total number of confirmed cases in Washington now stands at nine. Of the nine, four did not display clinical signs, and signs associated with other cases were not reported. There have been no equine deaths related to the outbreak in Washington. The EHV-1-positive horses are located in the following counties: Thurston, Spokane, Chelan, Asotin, and Whitman.

No Change

  • Arizona--14 positives (one euthanized; no clinical signs reported for surviving horses)
  • British Columbia--2 positives (clinical signs not reported)
  • California--22 positives (two horses were euthanized after showing severe neurologic signs; eight confirmed cases displayed neurologic signs; 13 displayed only a fever; one displayed only a nasal discharge)
  • Colorado--9 positives (six horses have shown neurologic signs; the remaining three have displayed respiratory signs and/or a fever)
  • Idaho--8 positives (four EHV-1 positive horses have displayed neurologic signs [two were euthanized]; the rest have only displayed a fever)
  • Nebraska--0 positives
  • Nevada--3 positives (two have displayed neurologic signs)
  • New Mexico--4 positives (USDA Situation Report indicates two have been euthanized; clinical signs not reported for other horses)
  • North Dakota--0 positives
  • Oklahoma--1 positive (displayed mild neurologic signs)
  • Oregon--5 positives (one euthanized with neurologic signs; four showing no clinical signs)
  • Saskatchewan--1 positive (no information about clinical signs released)
  • South Dakota--1 positive (clinical signs not reported)
  • Texas--1 positive (officials believe it is not related to the outbreak, but is an isolated case in a racing Quarter Horse)
  • Utah--8 positives (two euthanized after becoming recumbent, or unable to rise; clinical signs associated with the other confirmed cases were not reported)
  • Wyoming--0 positives

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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