Coital Exanthema

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Equine coital exanthema is caused by equine herpesvirus-3. The disease is spread through direct and sexual contact and has an incubation period of as little as two days. It is probably transmitted only in the acute phase by direct and sexual contact, but transmission via contaminated supplies and instruments is also known to occur in horses that have not been bred.

The virus is highly contagious, but is noninvasive and relatively benign. Systemic illness does not result, and neither infertility nor abortion occur when the horse becomes infected.

Signs of the disease include small blisters and ulcerations of the vagina, penis, prepuce, and perineum. The blisters burst and become infected by skin bacteria. Lesions may also be seen on the lips and teats. Although the lesions may heal within two weeks, the virus remains latent in the mare or stallion for life. When the lesions heal, they may leave depigmented white spots in the genital area.

The primary negative impact is the forced, temporary disruption of mating activities. Delayed foaling dates or reduced pregnancy rates occur in mares that miss breeding opportunities because of the disease. In stud operations, the disruptions affect the number of breeding dates for stallions.


  • Superficial lesions on the skin of external genitalia
  • Developing pustules progressing to a raw or encrusted ulcer
  • Localized inflammation
  • Whitish discharge, especially in stallions
  • Vulvar discharge in mares
  • Frequent urination or arching of back in mares
  • Loss of libido in stallions


Coital exanthema is caused by equine herpes virus type III (EHV-3). The only known source for the virus is an infected horse. Serological tests have shown that stallions and mares may acquire primary infection or reinfection by EHV-3 without exhibiting signs of clinical disease.

Epidemiological data suggest that the original source of an outbreak may be a visiting mare brought onto a stud farm for breeding, or the virus may be reactivated from a member of the resident stallion population.

Infection occurs by direct cutaneous contact either during coitus or by the transfer of virus-containing secretions from contaminated objects such as hands, gloves, instruments, sponges, or the lips or nose of an infected horse. The virus is easily transmitted by simple contact with the skin and the skin surface need not be damaged for infection to occur.


Since a commercial vaccine against EHV-3 has not been developed and because of the existence of latently infected carrier animals in most horse populations, a stringent code of practice to prevent infection should be enforced.

Heightened awareness of the signs of ECE will help handlers recognize and isolate any new clinical cases. Abrupt cessation of breeding of animals when any signs of the disease appear, and strict adherence to breeding procedures designed to eliminate transmission of the virus through either direct or mechanical contact are necessary.

Personnel assisting with the preparation of mares or stallions for breeding should be fully aware of the importance of early detection of new cases of ECE. Disposable examination sleeves and latex gloves should be changed between each horse being handled.

Mare preparation chutes should be washed down with water and disinfected between mares to prevent cross infection. A thorough rinsing of the stallion's penis and prepuce with plain warm water after each mating will reduce the potential for the virus to be transmitted.

All instruments, buckets, and devices used during breeding procedures should be washed and sterilized between uses or fitted with clean disposable covers or liners.


Genital lesions of ECE are usually characteristic enough in appearance for a clinical diagnosis to be made with reasonable certainty. If necessary, a diagnosis can be confirmed in the laboratory from specimens collected from the edges of fresh, active lesions by swabbing or scraping. This is usually done under the direction of a veterinarian.

Three categories of medicinals form the basis for most treatment regimens: anti-microbials for control of secondary bacterial infection of the lesions; antiseptics for cleansing and drying of the lesions; and anti-inflammatory agents.

All are applied daily as creams or ointments to the affected areas. During cleansing or application of creams or ointments, care should be taken to avoid accidental removal of the scabs or crusts of the healing sores.

Corticosteroids may slow the healing process, but can help reduce inflammation. The healing process may be speeded up by laser treatment of the lesions in conjunction with vitamin E ointment. In severely affected animals, antibiotics may be included to speed healing and prevent pyrexia or anorexia.

The quarantine time should be based on careful clinical evaluation of whether the genital lesions are still infective, rather than on a prescribed length of time. Lesions should be fully granulated and regressed to a point that likelihood of the virus still being active is low.

The quarantine time will vary from horse to horse. Careful management of the healing process and the prevention of bacterial infection will speed the recovery time for both mares and stallions

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EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.