Equine Coital Exanthema (ECE)

Other Names

ECE; equine herpesvirus type 3 infection; coital vesicular exanthema; genital exanthema.

What is Equine Coital Exanthema?

Equine Coital Exanthema (ECE) is a highly contagious venereal disease of horses caused by Equine Herpesvirus type 3 (EHV-3). The condition is characterised by the formation of pustules and ulcerated lesions on the external genitalia of both mares and stallions. It is transmitted almost exclusively through direct contact during mating, making breeding operations — particularly those using natural cover — the primary setting for outbreaks.

ECE is found worldwide and affects horses of all breeds and ages, though it is most clinically significant in breeding stock. It does not cause systemic illness, respiratory disease, or abortion, which distinguishes it from the more serious equine herpesviruses (EHV-1 and EHV-4). However, an active outbreak can disrupt an entire breeding season, making early identification and management essential for stud farms.

The disease is self-limiting and affected horses typically recover fully within three to four weeks with appropriate supportive care. The virus can establish a latent infection, meaning horses may carry EHV-3 asymptomatically and reactivate the disease under physiological stress.

Causes

ECE is caused by Equine Herpesvirus type 3 (EHV-3), a DNA virus that is distinct from EHV-1 (respiratory disease and abortion) and EHV-2 (mild respiratory illness). The virus is transmitted principally through direct genital contact during natural mating. Transmission via fomites — contaminated hands, equipment, gloves, and speculum — is well documented in clinical settings, making hygiene during reproductive examinations critical.

Artificial insemination with contaminated semen is also a recognised route of transmission, and insemination equipment that is not properly cleaned can spread the virus within a single breeding cycle. As with other herpesviruses, latent carriers can reactivate and shed virus under conditions of stress, immunosuppression, or corticosteroid administration.

Symptoms and Signs

Clinical signs appear three to eight days after exposure. In stallions:

Multiple, round, raised pustules on the penis, prepuce, and urethral opening
Pustules rupture to form shallow, well-defined ulcers
Lesions may crust over as healing progresses
Depigmented (white) spots frequently remain at healed lesion sites — a diagnostically useful sign

In mares:

Similar pustules and ulcers on the vulva, vaginal vestibule, and perineum
Discomfort or reluctance when the area is touched
Occasional vulval discharge if lesions become secondarily infected

Neither mares nor stallions typically show systemic signs such as fever, lethargy, or loss of appetite. The condition is painful locally, however, and affected stallions may be reluctant to mate.

Diagnosis

Diagnosis is usually made on the basis of clinical appearance and history — the characteristic genital ulcerations in a breeding animal with recent covering history are highly suggestive. Laboratory confirmation using virus isolation, PCR testing of swabs from active lesions, or immunofluorescence testing provides definitive diagnosis and distinguishes ECE from other causes of genital ulceration such as equine viral arteritis (EVA) or coital injury.

It is important to distinguish ECE from EVA, which also causes reproductive losses and has different regulatory implications. Your vet will advise on appropriate testing if the diagnosis is uncertain.

Treatment

There is no specific antiviral treatment for ECE. Management is supportive and focuses on preventing secondary bacterial infection of the lesions and keeping the horse comfortable. Topical antibiotic creams or ointments are commonly applied to prevent secondary infection. Gentle cleaning of the affected area with mild antiseptic solution is recommended.

Affected horses should be rested from covering or artificial insemination procedures until all lesions have fully healed — typically three to four weeks. Returning a horse to breeding activity before complete healing risks spreading the virus to other animals and may prolong the individual horse’s recovery.

Prevention

Strict biosecurity within breeding programmes is the cornerstone of prevention:

Inspect all breeding stock for genital lesions before each mating
Use disposable gloves and sterile equipment for all reproductive examinations
Disinfect and thoroughly clean all equipment between horses
Quarantine new horses before introducing them to a breeding programme
Avoid using stallions or mares with a history of unexplained genital lesions until cleared by a vet
For AI programmes, ensure semen collection and processing equipment is sterile

There is no commercially available vaccine for EHV-3 in the United Kingdom at the time of writing. Prevention relies entirely on management and hygiene protocols.

Prognosis

The prognosis for individual horses is excellent. ECE is self-limiting and horses recover fully within three to four weeks. Depigmented spots at healed lesion sites do not affect the horse’s health or breeding ability. The primary concern is not individual welfare but the disruption to a breeding season and the risk of spreading the virus through a stud if proper management is not applied.

When to Call the Vet

Contact your vet if you notice any lesions on the genitalia of breeding stock, particularly pustules or ulcerated areas that appear following recent mating. You should also call immediately if you suspect an outbreak at a stud, as rapid implementation of quarantine measures can limit the number of horses affected. Do not continue mating activities until your vet has assessed the situation.

Frequently Asked Questions

Does ECE affect the horse’s ability to breed in the future?

No. Once lesions have fully healed, affected horses return to normal breeding activity without any long-term consequences. Depigmented spots at healed sites are cosmetic only and do not impair fertility or cause discomfort.

Can ECE cause abortion or respiratory disease?

No. EHV-3 (the cause of ECE) is a distinct virus from EHV-1, which is associated with abortion and neurological disease, and EHV-4, which causes respiratory illness. ECE does not cause systemic disease and has no association with reproductive losses beyond the disruption caused by taking affected animals out of the breeding rotation during the healing period.

Can ECE be transmitted through artificial insemination?

Yes. If contaminated semen or non-sterile insemination equipment is used, the virus can be transmitted via artificial insemination. This is why strict hygiene protocols during semen collection and processing are essential in any AI programme.

How long should affected horses be rested from breeding?

Affected horses should be rested from all mating and insemination activities until all lesions have fully healed — typically a minimum of three to four weeks. Your vet should confirm complete healing before returning the animal to a breeding programme.

The British Equine Veterinary Association (BEVA) provides guidance on equine herpesvirus management and biosecurity for breeding operations.