The Equine Disease Communication Center (EDCC) reported Jan. 30 that a horse at Portland Meadows race track, in Oregon, has tested positive for equine herpesvirus-1 (EHV-1).

“The Oregon Department of Agriculture is reporting that … a 7-year old Thoroughbred mare developed mild ataxia on Jan. 25,” the EDCC said. “Neither the neuropathogenic or wild type strains of EHV-1 were detected by PCR testing on blood EDTA samples. The EHV-1 neuropathogenic strain was not detected by PCR testing on nasal swab samples, however, the wild type strain was detected.

"Portland Meadows race track veterinary authorities have quarantined the index case and high-risk contacts in a barn separate from other horses. Enhanced biosecurity measures have been implemented. The index case is stable and nonfebrile. High-risk contacts are being closely monitored. To date, there have been no additional sick animals reported.”

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 myeloencephalopathy (the neurologic form). In many horses, fever is the only sign of EHV-1 infection, 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.