Since Aug. 10, 16 horses at Brookhill Stables in Goble, Ore., and two horses from a nearby private farm have shown respiratory and/or neurologic signs consistent with equine herpesvirus type 1 (EHV-1), although not all were tested for the disease. At press time, three older victims had been euthanized–one from Brookhill Stables and two horses which visited Brookhill in early July from a private farm.

The Oregon State University’s (OSU) Veterinary Diagnostic Laboratory confirmed the presence of EHV-1 in three horses at the boarding facility, and the Gluck Equine Research Center at the University of Kentucky isolated the virus from three more horses using later samples. (The Gluck Center houses the national reference laboratory for equine herpesvirus in the United States.)

Don Mattson, DVM, PhD, a veterinary virologist at the OSU laboratory, said in a press release, “These samples showed extremely high antibody titers to EHV-1, much higher than we have ever seen. The fact that the antibody titer was very high, older horses were affected, and horses at the stable were alleged to be vaccinated against EHV-1 every three months, suggests that we may be dealing with a similar form of the virus (to the Ohio outbreaks early this year; see article #4214). This virus is very infectious and is spread by droplet aerosol and mechanically by handling exudates from animals that are just coming down with the disease.”

Attending veterinarian Katy Ostervold, DVM, of Valley Vet Clinic in Rainier, Ore., said that by Sept. 9, all but two horses had shown respiratory or neurologic signs, fever, and a rash at some point (only the yearling filly showed respiratory signs). Neurologic signs included ataxia and paresis (slight or incomplete paralysis), usually of the hindquarters; walking in tight circles; poor tail tone; and dribbling urine