EHV-1 Outbreak: USDA Releases Final Situation Report

The USDA Animal and Plant Health Inspection Service released its final situation report on the equine herpesvirus-1 (EHV-1) outbreak that affected the western United States and Canada starting in mid-May. The outbreak is believed to have stemmed from horses attending a national championship cutting competition held in Utah in early May. In its most recent report the USDA indicated that disease spread had been contained.

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.

The California Department of Food and Agriculture issued a press release June 20 indicating that animal health officials believe the outbreak has been successfully contained in that state. The release indicated that California has not diagnosed a new case of EHV-1 in the past 14 days.

"It is important that the California horse owners remain vigilant as there is always risk of disease when horses of unknown health status are commingled at one location," the release continued. "Consistent, basic biosecurity practices play an important role in reducing risk of exposure to diseases such as influenza, strangles, pigeon fever, or equine herpesvirus."

Newly confirmed cases continue to trickle in; however, animal health officials indicate that all of the new cases are under proper quarantine and are being treated.

At press time (2:30 p.m. EDT), the following states and provinces had confirmed new cases of EHV-1:

Wyoming--The first confirmed case of EHV-1 was reported in Wyoming in June 22, according to State Veterinarian Jim Logan, DVM. He confirmed that the horse displayed some neurologic signs including recumbency (not able to rise); however, after beginning treatment he was able to stand and is now in the recovery process. Logan added that the horse is in isolation and the farm he resides on in Jackson County is under quarantine.

He added that a second horse was euthanized after becoming recumbent, and test results are pending. Logan said he expects to have laboratory diagnostic test results early next week.

Saskatchewan--The University of Saskatchewan's Western College of Veterinary Medicine (WCVM) has placed its large animal hospital under a voluntary quarantine after a horse with a suspected case of EHV-1 was admitted June 18, according to a press release from the college.

"The WCVM voluntarily suspended its equine clinical services on June 21 following the confirmed diagnosis of EHV-1 in a horse from the Saskatoon area that was brought to the clinic on June 18," the release read. "While tests results are still pending, WCVM veterinarians suspect the horse was suffering from the neurologic form of EHV-1 ... the horse was humanely euthanized due to the severity of the disease."

One other EHV-1 positive horse was reported in Saskatchewan in May. No information was available about the animal's clinical signs.

Alberta--Thirteen cases of confirmed EHV-1 have been reported in Alberta, according to a report from the Office of the Chief Provincial Veterinarian. Four of these confirmed cases displayed neurologic signs associated with the disease, five exhibited only respiratory signs or a fever, and four did not have any clinical signs. One of the EHV-1 positive horses has died, and the rest are undergoing treatment, the report stated.

Additionally, two suspect cases are displaying neurologic signs, but have not been confirmed positive via laboratory diagnostic tests.

The report noted, "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."

Washington--A ninth horse has tested positive for EHV-1 in Washington state according to a report from the state's Department of Agriculture. Officials believe that this horse was exposed to the virus during the initial quarantine at Washington State University but did not display clinical signs. The report indicated that the horse recently suffered a bout of colic, at which point he tested positive for the virus. The horse's clinical signs were not reported. The EHV-1 positive horses are located in Thurston, Spokane, Chelan, Asotin, and Whitman counties.

The following states and provinces have not reported any change in the number of EHV-1 positive horses within their borders:

  • 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)
  • Montana--1 positive (no clinical signs displayed)
  • 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)
  • 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; clinical signs associated with the other confirmed cases were not reported)

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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