Four northern Virginia horses have exhibited cases of equine herpesvirus (EHV) myeloencephalopathy, a rare neurologic disease, according to TheHorse.com.
Three of the horses were euthanized, and a fourth is recovering.
EHV is a version of EHV type 1, known in respiratory form as rhinopneumonitis.
Veterinarians are on the lookout for other unusual symptoms.
Necropsies on the two horses submitted for testing have been inconclusive, says Joseph P. Garvin, DVM, laboratory director of the Virginia Department of Agriculture and Consumer Services' Warrenton Regional Animal Health Laboratory. Tests results were also inconclusive at the National Veterinary Services Laboratory in Ames, Iowa. Yet scientists have ruled out other possible neurologic diseases, including West Nile virus, equine encephalitis and Equine protozoal myeloencephalitis.
Garvin explained that tests of the tissue are conclusive only if EHV-1 is grown out from the tissue or its DNA is found through a sensitive laboratory test. Further complicating matters, the virus might not be present in the horses by the time of their deaths.
Usually horses with this disease will run a high fever prior to developing symptoms, but the horses had no fever, Garvin reports. However, each displayed hindlimb ataxia, loss of control of their bladder, a flaccid tail, and they eventually went down.
The neurologic form of EHV-1 often is cured with supportive care, but once a horse is down, it's difficult to nurse it back, which is why veterinarians elected to euthanize the horses.