EHV-1 Outbreak: USDA Releases New Report

A new USDA Animal and Plant Health Inspection Service report was released yesterday, indicating that the rate at which new cases of equine herpesvirus-1 (EHV-1) are confirmed is slowing. The current outbreak is believed to stem from a cutting horse championship competition in Utah, held in early May.

The most recent situation report from the USDA (published late on May 8) indicated that more than 85 horses have tested positive for EHV-1 in the United States. Additionally, although not reported by the USDA, more than 10 Canadian horses are also EHV-1 positive. A total of 13 horses have died or been euthanized in both countries combined.

As the rate of case diagnosis slows, more states are recommending horse owners cautiously return to business as usual.

In Washington the state Department of Agriculture issued a press release in which State Veterinarian Leonard Eldridge indicated that while it's safe for horses not exposed to EHV-1 to travel, affected horses should still be quarantined.

"I continue to recommend that horses that are confirmed positive for (neurologic) EHV-1 or were exposed to a positive case be isolated for 28 days after all symptoms have cleared up," Eldridge said in the press release. "While the animal may appear to have recovered, it can still transmit this highly contagious disease to another horse."

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.

Arizona--The current USDA situation report indicated that 14 horses have now tested positive for EHV-1. No information was provided as to what clinical signs the affected horses displayed; however, the USDA report noted that at least one EHV-1 positive horse had been euthanized or died.

At press time (4:30 p.m. EDT), the rest of the case counts remained the same in the following states and provinces:

  • Alberta-- 10 positives (four horses had no clinical signs but tested positive through laboratory testing, three had respiratory signs, and three displayed neurologic signs; one horse has died; however, it's unclear if that horse was neurologic or not)
  • British Columbia--2 positives (clinical signs not reported)
  • California--21 positives (Eight displayed neurologic signs [two of which were euthanized] and 13 horses have only been febrile)
  • 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--0 positives
  • 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 Quarter Horse racehorse)
  • Utah--8 positives (two euthanized after becoming recumbent, or unable to rise; clinical signs associated with the other confirmed cases were not reported)
  • Washington--8 positives (four did not display clinical signs; signs associated with other cases 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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