Sixteen horses at one facility in King County, Washington, have now tested positive for equine herpesvirus-1 (EHV-1), seven of which have been euthanized.

On Dec. 15, the Equine Disease Communication Center (EDCC) first reported that a 13-year-old Haflinger gelding had tested positive for EHV-1

In a Dec. 26 update, the EDCC said subsequent testing had revealed additional EHV-1 positive horses.

“Thirty-seven of 60 horses (at the facility) have now been tested with 16 horses confirmed positive for the equine herpesvirus-1 neurotropic strain,” the EDCC said. “Seven horses have been euthanized due to equine herpesvirus myeloencepalopathy (EHM). Clinical signs of the EHM horses included 102-105°F fevers, hind-limb ataxia, no tail tone and dribbling urine. Treatment of horses include supportive care and anti-viral therapy.

“The attending veterinarian is making morning and evening rounds at the barn and evaluating fevers and clinical signs,” the statement continued. “The horse facility is still under quarantine and strict equine biosecurity in place. At this time no other horse facilities are reporting new cases in the state of Washington.”

[brightcove videoid="3027535698001" title="Health Alert: Equine Herpesvirus"]

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.