EHV-1 Outbreak: Case Total Holding Steady

Horse owners in the western United States and Canada remain on alert for neurologic equine herpesvirus-1 (EHV-1). The outbreak--which is believed to have originated from horses that attended the April 29-May 8 National Cutting Horse Association's (NCHA) Western National Championship competition in Ogden, Utah--has caused the cancellation or postponement of numerous equestrian events throughout the Western states.

A statement released late yesterday (May 23) by the NCHA indicated that all NCHA-approved competitions this upcoming weekend (May 27-29) have been canceled, in addition to the NCHA/American Quarter Horse Association (AQHA) Weekend (a grassroots cutting "celebration" held annually). The latter event was scheduled for June 3-5 at 25 locations around the United States.

The AQHA also made the decision to lower the number of qualifying points horses need to amass for inclusion in the Adequan Select World Championship Show (scheduled for Aug. 28-Sept. 3 in Amarillo, Texas), according to a statement on the organization's website. The decision, made by the AQHA Executive Committee, came after "several show managers ... either voluntarily canceled or are considering cancelation of their shows this weekend, and some exhibitors have expressed their reluctance to move their horses out of concern of potentially exposing them to EHV-1."

The concern is not limited to the cutting and Quarter Horse communities, however, as two eventing facilities released press releases in regards to upcoming competitions on the United States Eventing Association's website. A nationally recognized horse trial in Montana slated to take place May 27-28 was rescheduled to July for precautionary measures, and another nationally recognized horse trial taking place in California this weekend has implemented numerous biosecurity measures: For example, horse health certificates issued within 72 hours of arriving on show grounds must be presented, and all horses will undergo a veterinary health inspection upon arrival.

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.

At press time, only two states had reported updated information regarding the EHV-1 cases:

Washington - The Washington Department of Agriculture noted today in a statement that no new positive cases were reported, leaving the total at six confirmed cases. The horses with confirmed cases are located in the following counties: Thurston in Western Washington, Spokane in Eastern Washington, Chelan in Central Washington, and Asotin and Whitman in Southeast Washington. Two of the confirmed cases (both located at Washington State University's Veterinary Teaching Hospital) were only febrile, and it is not known if the remainder of the confirmed cases displayed neurologic signs.

A press release received today from the Texas Animal Health Commission (TAHC) noted that, "Currently, there are still 25 known horses in Texas that attended the event and 336 cohorts stablemates ... currently being held under movement restrictions. The single confirmed case which was a horse from New Mexico that sought treatment in a veterinary clinic in Texas is now recovering. The horse returned to its original premises of origin. The single suspect(ed) case that was reported May 19 from Jack County tested negative for EHV-1, however was euthanized due to the severity of (an) unrelated illness. TAHC continues to evaluate other unrelated horses with clinical signs, but no additional cases have been confirmed at this time."

No New Cases

No new confirmed cases of EHV-1 were reported in Colorado today, according to a statement from the Department of Agriculture. The total stands at nine confirmed cases and 22 suspected cases.

At press time, there was no new information from the California Department of Food and Agriculture. A statement issued yesterday indicated that there were 18 confirmed cases in the state, of which seven displayed neurologic clinical signs. Similarly, at press time, no new cases had been reported in Idaho or Oregon, leaving their totals at one and three, respectively.

Arizona and New Mexico remain at one confirmed case each, according to the regulatory bodies in each state. Both horses were euthanized after each displayed neurologic signs.

Montana, Nebraska, Nevada, South Dakota, and Wyoming (all of which are home to horses that competed at the NCHA competition) remain free of confirmed EHV-1 cases.

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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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