The following information was posted on The Ohio State University Veterinary Teaching Hospital’s web site Feb. 26. The author, Catherine W. Kohn, VMD, Dipl. ACVIM, is professor of equine medicine and surgery at OSU.

Typical Clinical Signs of EHV-1 Infection
 
Upper respiratory infection is the most common manifestation of EHV-1 infection. Commonly, young horses (weanlings, yearlings, and 2 year olds) have depression, poor appetite, nasal discharge and cough. If young horses are housed or pastured together, many horses in the herd may experience disease from which they recover uneventfully. Disease may be mild or unapparent in older horses.
 
EHV-1 infection in pregnant mares may result in abortion. Appropriate vaccination has greatly reduced the incidence of outbreaks of virus abortion on breeding farms.

Less typical Clinical Signs of EHV-1 Infection
 
Neurological signs occur infrequently as a result of EHV-1 infection; however, outbreaks of neurologic disease associated with fever, nasal discharge and cough have been reported both in the USA and elsewhere (see below). Neurologic signs may include incoordination that can progress to an inability to stand. Horses may be unable to urinate or may dribble small volumes of urine. Horses may have difficulty producing manure. Sometimes the neurologic signs are accompanied by cellulitis (inflammation or swelling of the limbs) and petechiae (small hemorrhages on the gums)
 
Pathogenesis of EHV-1 Infection
 
The primary reason that EHV-1 causes disease is that it causes vasculitis (inflammation of the endothelial cells that line blood vessels). Vasculitis of the brain and spinal cord are the most common abnormalities seen under the microscope in tissues from horses that die of the neurological form of this disease. Vasculitis elsewhere in the body is less commonly encoun