The California Department of Food and Agriculture (CDFA) has announced additional confirmed cases of equine herpesvirus-1 (EHV-1) in horses residing an already quarantined facility in Orange County.

On April 24 the CDFA reported that a febrile horse which initially tested negative was resampled and confirmed positive for EHV-1.“This horse has been placed in isolation on the premises,” the agency said.

The first positive horse displayed a fever on Monday and was placed in onsite isolation stabling,” the department said. “The second positive horse initially tested negative over the weekend and was moved off-site for isolation and quarantine.

“Enhanced biosecurity measures and twice daily temperature recording for all exposed horses in the quarantine barn continues,” the CDFA said. “To date, there have been seven confirmed febrile cases of EHV-1 and the one index case of equine herpesvirus myeloencephalopathy (EHM, the neurologic form of the virus).”

The index EHM case—a 17-year-old Thoroughbred gelding—remains quarantined and isolated offsite and continues to show clinical improvements, the CDFA said.

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 EHM. In many horses, the 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 EHV-1.

Horses with the neurologic form usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.