An attending veterinarian in Missouri confirmed on Oct. 16 that an Oregon County horse tested positive for equine herpesvirus myeloencephalopathy (EHM, the neurologic form of herpesvirus) and two additional horses were exposed. The positive horse, a 7-year-old Quarter Horse gelding with unknown vaccination history, began experiencing clinical signs of fever, nasal discharge, and hind limb neurologic signs on Oct. 13. The horse is reported as recovering.

EHV 101

Equine herpesvirus (EHV) 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 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.

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