New EHV-1 cases emerge in California

Sonoma County, Calif. — Three cases of the same neurotropathogenic strain of equine herpesvirus (EHV-1) that sickened more than two dozen horses during an outbreak in May have been confirmed on a single ranch in Sonoma County, but animal health officials say the two outbreaks are unrelated.

The California Department of Food and Agriculture (CDFA) confirmed the first case in a 15-year-old Oldenburg mare Aug. 23. The mare was isolated, quarantined and began treatment at a veterinary referral hospital, says CDFA. Two additional horses on the same ranch were confirmed to have neurotropathogenic EHV-1 Aug. 24, with the only clinical sign displayed among the two being a fever.

The ranch that housed the horses is under veterinary observation, with another 13 potentially exposed horses being tested twice daily, CDFA says. The ranch will be monitored and quarantined 21 days from the onset of clinical signs in the last confirmed EHV-1 case, according to CDFA.

CDFA says its epidemiologic investigation shows minimal risk of the disease spreading from the premises and that there is no direct link between these cases and the May EHV-1 outbreak that sickened nearly 90 horses across 10 Western states.