Eight California Horses Showing Signs of EHV-1

Updated Sept. 16 to reflect revised information from the California Department of FOod and Agriculture.

Eight additional horses in Tuolumne County, Calif., are exhibiting clinical signs consistent with equine herpesvirus-1 (EHV-1) after a mare in that county tested positive for the neurologic form of the virus on Sept. 12, according to a statement from the California Department of Food and Agriculture (CDFA). The exact clinical signs each horse are displayed were not reported.

The initial confirmed positive mare, who was being treated at a referral hospital, has shown improvement and was returned to her quarantined premises in Tuolumne County for recovery, the statement said.

"Epidemiologic investigation is ongoing and the premises owner and CDFA has contacted potentially exposed horse owners that visited the affected premises over the past two weeks," the release read. "On Sept. 13 University of California, Davis, veterinary school staff collected samples (blood and nasal swabs) from 150 animals on the premises, including the eight demonstrating compatible clinical signs. Test results are anticipated within the next few days."

Steve Lyle, director of public affairs for the CDFA, stressed that only one horse has been confirmed as EHV-1 positive in Tuolumne County to date.

Further, the CDFA has relayed that a horse that participated in the Sept. 10 American Competitive Trail Horse Association Ride for Mustangs was exposed to the index horse prior to taking part in the ride.

"The exposure occurred prior to the ride and the exposed horse has not displayed any signs of disease," the release noted. "However, out of an abundance of caution, CDFA has contacted all ride participants to recommend isolation and temperature monitoring of horses which participated in the ride for 14 days from the last exposure."

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. Should a horse display the aforementioned clinical signs and has been potentially exposed to the virus, a veterinarian should be called quickly to obtain samples and test for the disease.

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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