The Equine Disease Communication Center (EDCC) reported May 29 that the Texas Animal Health Commission (TAHC) confirmed equine herpes myeloencephalopathy (EHM, the neurologic form of equine herpesvirus-1, EHV-1), in a Williamson County barrel racing horse on May 24.

This is the third EHM case diagnosed in Texas horses this month.

“The newly identified horse showed signs of nasal discharge and ataxia when evaluated by a local veterinarian and EHV-1 was confirmed by a recognized laboratory,” the EDCC statement said. “The premises is under movement restrictions and TAHC staff (are) working closely with the owner and veterinarian to monitor potentially exposed horses and implement biosecurity measures.

“Prior to confirmation of EHM, the horse attended a private training facility in Liberty Hill, Texas, on May 11 and barrel racing events at the Killeen Rodeo Outdoor Arena on May 12 and Williamson County Expo Center on May 5,” the EDCC said. “(The) TAHC has contacted event management, veterinarians, and the training facility to ensure enhanced surveillance and biosecurity measures are taken.”

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.