EHV-1: California and Tennessee Case Counts Holding Steady

As two different states handle unrelated equine herpesvirus-1 (EHV-1) outbreaks, statements released by the California Department of Food and Agriculture (CDFA) and the University of Tennessee Veterinary Medical Center (UTVMC) indicate that case totals are holding steady.

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 with potential EHV-1 exposure display any of the aforementioned clinical signs, a veterinarian should be called to obtain samples and test for the disease.


The CDFA reported no new cases of the virus have been confirmed since Sept. 15. Two facilities remain under quarantine: the index premises located in Tuolumne County and a secondary premises located in San Joaquin County.

A total of eight horses tested positive for the neurologic strain of EHV-1 at the Tuolumne County facility, including the index horse who was confirmed positive for the disease on Sept. 12, the statement read. Six of the eight affected horses displayed neurologic signs while two only exhibited a fever. The statement noted that one of the EHV-1 positive horses was euthanized as a result of the disease.

"Owners of horses which have visited the premises during a two week period prior to start of the outbreak have been contacted by CDFA and asked to isolate and monitor their exposed horse(s) for 14 days," the statement added.

Two horses residing on the secondary San Joaquin County premises have also been confirmed as EHV-1 positive, the statement said, adding that both animals were exposed to the virus while visiting the Tuolumne County premises between Sept. 4-10.

The statement noted that one of the horses has displayed neurologic signs consistent with EHV-1 while the other has only exhibited a fever.

"Epidemiologic investigation conducted by CDFA reveals minimal risk of disease spread beyond this facility due to early detection of disease and immediate isolation of horses post exposure," the CDFA added.


In a statement released yesterday (Sept. 22) the UTVMC indicated that no additional horses have exhibited clinical signs consistent with EHV-1 or have tested positive for EHV-1. The hospital reported Sept. 21 that five additional horses had tested positive since the index case was diagnosed and euthanized at the UTVMC on Sept. 15.

The newly confirmed cases have not been admitted to the UT Veterinary Medical Center, but were confirmed positive on the same premises the index case had been residing. The statement indicated that the horses are quarantined and recovering at the Dixie Stampede. The clinical signs the newly confirmed horses displayed--if any--were not reported.

"In working with local veterinarians and the Tennessee Department of Agriculture, our equine faculty has not identified any cases of EHV-1 outside the index premise," the statement added.

The hospital remains under a seven-day quarantine implemented by the Tennessee State Veterinarian and a self-imposed 14-day quarantine, both of which began on Sept. 16.

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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