The Maryland Department of Agriculture has placed three facilities in that state under quarantine because horses residing there had traveled in late February to a Virginia farm at which horses tested positive for equine herpesvirus-1 (EHV-1), the Equine Disease Communication Center (EDCC) reported March 9.

“One farm in Montgomery County reported a horse with a fever that did test positive on blood only, not on the nasal swabs, on March 5,” the EDCC said. “A horse was reported with a fever on a farm in Calvert County on March 7 but tested negative on blood and swabs both on March 8. The third farm in St. Mary’s County reports that all horses remain afebrile. All three farms remain under hold orders. No horses have displayed any neurologic signs.”

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 (the neurologic form). 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