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Deadly Virus Infects 10 California Horses

State Department of Food and Agriculture declares an EHM 'outbreak.' Equestrian events canceled.

Ten confirmed cases of equine herpes myeloencephalopathy (EHM) in California were reported Tuesday by the state Department of Food and Agriculture.

In its statement, the department referred to the infection of 10 horses with the deadly virus as an "outbreak."

“This disease outbreak is evolving, and [the department] will continue to investigate cases and provide updated information,” the statement said.

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The Veterinary Infection Control Society has reported 15 confirmed cases in Washington, Colorado, California and Alberta, Canada, with 13 additional cases suspected in the western U.S. and two more in Canada.

The horses that have been confirmed as having EHM in California are located in Kern, Placer, Stanislaus, Amador and Napa counties. All of the horses that tested positive for EHM had recently attended the National Cutting Horse Association’s Western National Championships in Ogden, UT. One other horse died in Bakersfield after exhibiting neurological signs of the disease.

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Of the 500 horses that attended the championships in Utah, 54 returned to California after the show. Contacted by the Department of Food and Agriculture, their owners were asked to isolate and monitor the horses. Two of those horses were confirmed to have EHM last week, and one of them has died.

No information has been provided regarding hauling horses across state lines, although Colorado and other states have closed their borders to inbound and outbound horses. 

Many large equestrian facilities are closing until the outbreak is contained, such as the Murieta Equestrian Center in Rancho Murieta and the Buckeye Event Center in Buckeye, AZ.  Although no horses have reportedly shown symptoms of EHM at either of the facilities, both issued statements that they were closing as a precautionary measure.

The Sundance Feedlot in Bakersfield has been quarantined, and all events scheduled there have been canceled as a result of the outbreak. Twenty-five horses remain there under quarantine after two horses exhibited signs of EHM and one died upon arriving there from Ogden, UT, for a cutting event.

Event producers are responding statewide by canceling or postponing events in order to keep horses home in the event they have been exposed to the virus. Many local events such as the National Barrel Horse Association barrel race in Acton and the Simi Valley Riders' two-day gymkhana scheduled for this weekend have been canceled. 

The National Cutting Horse Association has canceled all cutting events in the western U.S. until the EHM situation is contained.

Chatsworth veterinarian Marta Granstedt told Chatsworth Patch that in the event horses are exposed to EHM, they should be isolated.

"Monitor their temperature two times per day for two weeks," she said. "If they go two weeks without a fever, vaccinate, then booster.”

Granstedt also advised that horses be given a booster if they have not been vaccinated in the past three months for the virus, EHV-1. Most regular vaccinations include EHV-1 (sometimes referred to as “rhino”) as a regular course of treatment. 

“No matter what vaccine is used or how many times you vaccinate a horse, it is foolish and inaccurate to assume they are protected from neurological rhino," Granstedt warned. "Keep your eyes open and use good common sense.”

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