Nine California Horses Confirmed EHV-1 Positive

Nine California Horses Confirmed EHV-1 Positive

Neurologic EHV-1 is characterized by fever, ataxia (incoordination), weakness or paralysis of the hind limbs, and incontinence.

Photo: Stephanie L. Church, Editor-in-Chief

Less than a week after a mare from Tuolumne County, Calif., tested positive for the neurologic strain of equine herpesvirus-1 (EHV-1), seven other horses residing on her home premises have tested positive for the virus, according to a statement from the California Department of Food and Agriculture (CDFA). Further, a second premises has been quarantined after two horses residing there tested positive for the virus.

"Seven of the eight horses displaying compatible clinical signs at the quarantined premises have been confirmed positive for neuropathogenic strain of EHV-1," the Sept. 15 statement read. "Five of the confirmed cases have displayed neurologic signs and two of the cases have only demonstrated a fever. One of the severely affected neurologic confirmed cases has been euthanized."

The statement also noted that the mare that initially tested positive on Sept. 12 made improvement at the referral hospital she was being treated at, and was returned to the quarantined premises, where she continues to recover.

Also on Sept. 15, the CDFA indicated that a second premises in San Joaquin County has been quarantined in relation to the Tuolumne County outbreak.

"Two horses displaying compatible clinical signs were confirmed positive for the neuropathogenic strain of EHV-1," the department's statement read. "These two horses were exposed to the virus on Sept. 4-10, while visiting the Tuolumne county premises. Both horses have been isolated and the premises has been quarantined."

The CDFA added that the organization is conducting an epidemiologic investigation into the San Joaquin County situation as well.

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.

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.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from Learn More