The Equine Disease Communication Center (EDCC) reported Feb. 13 that three mares on a single facility in Bannock County, Idaho, have tested positive for the neurologic strain of equine herpesvirus-1 (EHV-1).

“Three Quarter Horse mares showed an onset of clinical symptoms including fever, ataxia, and neurological symptoms,” the EDCC said. “Two of the affected mares were euthanized. The premises is under quarantine and strict biosecurity is being followed. The epidemiological investigation is ongoing.”

The EDCC reported that this is the fourth Idaho premises to be quarantined due to EHV-1 in 2018.

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 equine herpesvirus myeloencephalopathy (the neurologic form). 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.