A 17-year-old Thoroughbred gelding from an Orange Country, California, facility has been diagnosed with equine herpesvirus myeloencephalopathy (EHM, the neurologic form of equine herpesvirus-1 [EHV-1]) after developing neurologic signs of disease, the California Department of Food and Agriculture (CDFA) reported April 13.
“The gelding has been isolated and placed under quarantine,” the CDFA’s statement said. “Exposed horses will be monitored for clinical signs and temperatures will be taken twice daily. Any horse displaying a fever or compatible clinical signs will be tested.”
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.