Equine coital exanthema is a benign venereal disease of horses that likely occurs worldwide. It affects both sexes and is caused by equine herpesvirus type 3 (EHV-3). This virus has a single antigenic type but also has small and large plaque variants in tissue culture, indicating that variation may occur in the severity of field outbreaks. Although the primary route of transmission is venereal, outbreaks have been documented in which transmission occurred via contaminated supplies and instruments or by the use of a single glove for rectal examination of many mares. It is probably for this reason that EHV-3 has also been isolated from horses that have not been bred.