FieldDxEquine coital exanthemaClinical signs, differential diagnosis, treatment and prevention in horses.
Overview
A mild venereal viral disease of horses causing genital nodules and ulcers without systemic illness, infertility or abortion. Equine herpesvirus 3, which has one antigenic type with small- and large-plaque variants.
Clinical signs
- Mares: red nodules up to 2 mm on the vulva, vagina, clitoris and perineum that progress to painful ulcers, sometimes with perineal oedema.
- Secondary Streptococcus infection can enlarge ulcers, cause discharge and produce fever.
- Skin lesions heal in about 3 weeks; vaginal and clitoral ulcers heal more slowly, and scars persist without reducing pregnancy rates.
- Stallions: similar lesions on the penis and prepuce; intromission is painful and bleeding ulcers can reduce sperm viability.
Predisposing factors
- Spread mainly by sexual contact, and by contaminated instruments, supplies or one glove used on many mares.
- Horses appear to shed virus mainly during the acute phase; whether a carrier state exists is unclear.
- Immunity is short-lived, though recurrence within one breeding season is unlikely.
Treatment
No vaccine or specific treatment exists; sexual rest allows lesions to heal and prevents further transmission, and secondarily infected ulcers may need an antimicrobial ointment.
Prevention
1. Sexual rest until lesions heal, and isolate affected horses until all lesions have healed. 2. Use disposable equipment for examinations. 3. Breed affected mares only by artificial insemination during the acute phase. 4. Examine horses carefully before breeding, allowing an incubation period of up to 10 days. 5.
Source
MSD Veterinary Manual — Equine Coital Exanthema (accessed 2026-08-12)
MSD Veterinary Manual — Equine Coital Exanthema (accessed 2026-10-29)
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