Officials at the California Department of Food and Agriculture (CDFA) have released the quarantine of an Alameda County premises where 44 horses were exposed to equine herpesvirus-1 (EHV-1) in mid-March. | Photo: Wikimedia Commons

The quarantine began on March 14 when a 14-year-old pony mare presented with neurologic signs and subsequently tested positive for EHV-1. In the weeks following, 10 additional horses on the premises tested positive, although none exhibited neurologic signs. All horses that tested positive have had two negative tests seven days apart.

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 EHV-1