On Dec. 5, California Department of Food and Agriculture (CDFA) officials confirmed a horse in Ventura County with neurologic equine herpesvirus (EHV-1, non-neuropathic strain). The 13-year-old Quarter Horse mare, which had been vaccinated in October, began showing signs of dysuria (painful or difficult urination) about Nov. 23 and presented to her attending veterinarian on Nov. 30 when her signs progressed to include fever, ataxia (inability to control bodily movements), peritonitis, urinary infection, and urine retention. She remains quarantined and receiving supportive care at a veterinary hospital. She had no recent travel or show history.

Thirty-two additional horses at the mare’s boarding facility remain under official quarantine with enhanced biosecurity measures in place following assessment by CDFA staff, who will continue monitoring the situation.

EHV 101

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and equine herpesvirus myeloencephalitis (EHM, the neurologic form).

In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months) but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with