Equine Coital Exanthema (ECE): Symptoms, Treatment & Prevention

Equine coital exanthema is a sexually transmitted viral infection in horses. Confirmed cases of this condition can have significant consequences, as affected horses must be withdrawn from breeding. Even a mild case can cause significant discomfort and disrupt breeding plans.

Any unexplained change around the genital area warrants prompt veterinary attention, particularly during breeding season. Early recognition helps protect breeding partners, limit farm-wide exposure, and rule out other causes of genital lesions.

Because the virus may persist after the skin has healed, managing ECE extends beyond the immediate episode. Keep reading to learn how owners and breeding managers can recognize the disease, respond to an outbreak, and make informed decisions about returning affected horses to breeding.

Equine Coital Exanthema (ECE)

Equine coital exanthema (ECE) is a contagious reproductive disease caused by equine herpesvirus type 3 (EHV-3). The virus primarily affects the external genital tissues of mares and stallions, causing small blisters that develop into painful ulcers. ^[1]

EHV-3 is transmitted primarily through direct contact during breeding, making ECE an important concern on breeding farms. Affected horses must be temporarily removed from breeding while lesions heal. ECE can disrupt breeding schedules and increase the risk of transmission to other horses. ^[2]

Unlike some other equine herpesviruses, EHV-3 infection usually remains limited to the genital area and does not cause widespread illness. Most affected horses otherwise appear healthy, and the disease does not typically cause long-term reproductive problems. ^[1][2]

Following infection, EHV-3 can remain dormant for life and may become active again later. Recognizing suspicious genital lesions and using appropriate breeding hygiene and biosecurity measures are important for limiting the spread of ECE. ^[1][2]

Table 1. Equine coital exanthema at-a-glance

Symptoms

Clinical signs of equine coital exanthema primarily affect the external genital area. Lesions usually begin as small, raised spots or fluid-filled blisters. These blisters rupture and develop into shallow, painful ulcers. ^[1][3][4]

Most skin lesions heal within about three weeks unless a secondary bacterial infection develops. Ulcers affecting the clitoris or vagina may take longer to heal, and pale or unpigmented scars can remain after the active lesions resolve. ^[1][3][4]

Affected horses generally remain bright and healthy, so changes around the genital area may be the only obvious sign of infection.

Signs in Mares

In mares, ECE lesions typically develop on the vulva and surrounding skin. Horse owners may notice: ^[3][4][5]

• Small, raised spots or fluid-filled blisters on the vulva
• Shallow, painful ulcers as the blisters rupture
• Swelling and redness around the vulva
• Tenderness or sensitivity around affected areas
• Reluctance to accept a stallion
• Discomfort during breeding
• Mild genital discharge in some mares
• Pale or depigmented spots where lesions have healed

These lesions can make breeding painful and may cause the mare to resist a stallion.

Signs in Stallions

In stallions, lesions most commonly develop on the penis and sheath. Signs can include: ^[3][4][5]

• Small blisters or ulcers on the penis or sheath
• Localized swelling and redness
• Pain or sensitivity around affected tissues
• Discomfort during erection or breeding
• Reluctance to breed
• Pale or depigmented areas after lesions heal

Because affected stallions may otherwise appear healthy, careful examination before breeding is important.

Systemic Signs

ECE usually affects only the genital area, and veterinarians rarely report signs involving the whole body. Most affected horses remain otherwise healthy. ^[1][2]

Rare reports describe horses developing fever, dullness, or loss of appetite. These signs have been more pronounced in stallions than in mares. Stallions with extensive genital lesions may also show reduced interest in breeding or refuse to mate. ^[6]

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When to Call the Veterinarian

Contact your veterinarian promptly if you notice blisters, ulcers, swelling, discharge, pain, or other unexplained changes around a mare’s or stallion’s genital area, especially during breeding season. ECE can resemble other reproductive or skin conditions, so veterinary examination and laboratory testing may be needed to confirm the cause.

Call your veterinarian before breeding if:

• A mare or stallion has small raised spots, blisters, ulcers, or pale healing marks around the genital area
• The horse shows swelling, redness, tenderness, discharge, or discomfort during breeding
• A mare becomes reluctant to accept a stallion or a stallion becomes reluctant to breed
• A horse has recently bred with an affected or suspicious horse
• Genital lesions do not improve, worsen, or appear infected
• The horse develops fever, dullness, loss of appetite, or other signs beyond the genital area

Do not breed a horse with suspicious genital lesions until it has been examined by a veterinarian. Early veterinary assessment helps protect breeding partners, reduce transmission risk, and determine when it is appropriate for the horse to return to breeding. ^[1][4]

Causes of ECE

Equine coital exanthema is caused by equine herpesvirus type 3 (EHV-3). This virus mainly infects the skin and tissues of the external reproductive tract. When EHV-3 infects these tissues, it damages surface cells and causes the characteristic blisters and ulcers associated with ECE. ^[1][4]

Equine Herpesvirus Type 3 (EHV-3)

Several types of equine herpesvirus can infect horses. EHV-3 differs from the herpesviruses horse owners may be more familiar with, including EHV-1 and EHV-4. ^[1][7]

EHV-1 can cause respiratory disease, abortion, and neurological disease, while EHV-4 is primarily associated with respiratory illness. In contrast, EHV-3 mainly causes external genital lesions and is responsible for equine coital exanthema. ^[1][4][7]

After EHV-3 infects the genital tissues, small raised spots and blisters develop. These blisters eventually rupture, leaving shallow, painful ulcers.

Latent Infection & Reactivation

Like other herpesviruses, EHV-3 can remain dormant in a horse’s body after the initial infection. This state is known as latency. ^[1][7][8]

The virus can later reactivate and be shed even when a horse shows no obvious signs of ECE. In one study, EHV-3 was detected in 6% of 220 Thoroughbred mares without clinical signs at the time of breeding. Researchers also documented periods of reactivation and viral shedding in previously infected mares kept in isolation. ^[9]

Because EHV-3 can establish a latent infection, controlling ECE depends on recognizing active disease, reducing exposure during breeding, and maintaining good hygiene and biosecurity. ^[1][4][8][9]

Transmission

EHV-3 spreads primarily through direct contact during breeding. Horses with active genital lesions can transmit the virus to a breeding partner, making ECE particularly important in breeding populations. ^[1]

The virus can also spread without breeding through contaminated objects or close contact between horses, including genital-to-nasal contact. ^[3]

Sexual Transmission

Natural breeding is the primary route of EHV-3 transmission. When an infected mare or stallion has active lesions, direct genital contact can expose the breeding partner to the virus. ^[3]

Because early lesions may be small or difficult to notice, an infected horse may be bred before ECE is recognized. Horses with suspected or confirmed ECE should be removed from breeding until lesions have healed.

Artificial Insemination

Artificial insemination avoids the direct genital-to-genital contact that occurs during natural breeding and can therefore reduce opportunities for EHV-3 transmission. However, the virus may still be transferred on contaminated equipment, gloves, or other materials used during semen collection and reproductive procedures. ^[2]

This underscores the importance of good hygiene in managing reproductive horses during artificial insemination procedures.

Indirect Transmission

EHV-3 can also spread without breeding. Contaminated objects, known as fomites, can carry infectious material between horses. Close interactions between horses, including genital-to-nasal contact, may also contribute to transmission. ^[1][5]

Stable flies and urine have previously been suggested as possible sources of transmission, but continued advances in equine medicine suggest these vectors are not transmission routes of EHV-3. ^[3]

Potential sources of indirect transmission include: ^[3]

• Reproductive equipment
• Veterinary examination instruments
• Contaminated gloves
• Human hands
• Other items contaminated with material from active lesions

Careful handling and disinfection help prevent these materials from carrying the virus between horses.

Risk Factors

Horses involved in breeding have higher chances of exposure to EHV-3. Risk increases with close reproductive contact or when poor hygiene allows infected material to move between animals.

Factors that can increase the risk of ECE include: ^[1][2]

• Natural-cover breeding
• Breeding with horses of unknown health status
• Introducing new mares or stallions into a breeding population
• Breeding horses with unexplained genital lesions
• Previous EHV-3 infection and reactivation of the virus
• Poor hygiene during reproductive examinations
• Sharing reproductive equipment without appropriate cleaning and disinfection
• Frequent movement of breeding horses between farms

Routine examination of breeding horses and consistent hygiene practices can help reduce the risk of EHV-3 spreading through a breeding population.

Diagnosis

Contact your veterinarian if you notice blisters, ulcers, swelling, or other unexplained changes around your horse’s genital area, particularly if the horse is actively breeding. ^[1][4]

Veterinarians may suspect ECE based on the appearance and location of the lesions and the horse’s recent breeding history. Laboratory testing can confirm EHV-3 infection. ^[1]

Your veterinarian will examine the external genital area for blisters, ulcers, swelling, redness, and healing lesions. ^[1][4]

The appearance of ECE changes as the infection progresses. Early lesions may appear as small blisters, while older lesions may be open, crusted, or healing. Pale areas of skin may remain after the active lesions disappear. ^[4]

Polymerase chain reaction (PCR) testing can confirm EHV-3 infection by detecting genetic material from the virus. Samples are typically collected from the edge of a fresh, active genital lesion and sent out for testing. ^[1][3][10]

Differential Diagnosis

Several conditions can cause genital sores, swelling, or inflammation that may resemble ECE. Other potential causes of similar signs include: ^[4]

• Injuries or irritation associated with breeding
• Other causes of inflammation of the vulva or vagina in mares
• Secondary bacterial infection of genital lesions

Because several reproductive conditions can cause similar signs, veterinary examination and laboratory testing may be needed to confirm EHV-3 infection.

Treatment

There is no specific treatment that eliminates EHV-3 from an infected horse. ECE is usually self-limiting, meaning the lesions generally heal with time and supportive care. ^[3]

Owners should temporarily remove affected horses from breeding while active lesions are present. Lesions usually heal within two to three weeks, although secondary bacterial infection can delay healing. Continuing to breed a horse with active lesions can cause pain, further irritate damaged tissues, and spread the virus to other horses. ^[1][4]

Supportive measures to help protect damaged tissues while the lesions resolve include: ^[1][5]

• Stopping breeding until lesions have healed
• Keeping affected areas clean and dry
• Protecting lesions from additional irritation or injury
• Providing pain relief if recommended by your veterinarian
• Treating secondary bacterial infections if they develop
• Monitoring lesions as they heal

Owners should consult their veterinarian before applying medications or topical products to genital lesions.

Although the visible lesions resolve, treatment does not eliminate EHV-3 from the horse’s body. The virus can remain dormant after recovery and may reactivate later. ^[7]

Prognosis

The prognosis for horses with equine coital exanthema is generally excellent. Most skin lesions heal within about three weeks unless a secondary bacterial infection develops, although ulcers affecting the vagina may take longer to heal. ^[4]

Pale or unpigmented scars can remain where lesions occurred, but these changes are mainly cosmetic. ECE does not appear to reduce pregnancy rates. ^[4]

Although the outlook for individual horses is good, ECE can have a greater impact on breeding operations. Temporarily stopping breeding while lesions heal can disrupt mating schedules and reduce reproductive efficiency. ^[3]

Recovery from an episode of ECE does not eliminate EHV-3 from the horse’s body. The virus can remain dormant for prolonged periods, allowing infected horses to remain asymptomatic carriers and potentially contribute to future transmission. ^[7]

Impact on Breeding Operations

Although ECE does not typically cause permanent fertility problems, an outbreak can have economic consequences for breeding farms and horse owners. Affected mares and stallions must be temporarily removed from breeding while lesions heal, which can delay breeding schedules and result in missed opportunities. ^[2]

For mare owners, a delay may mean missing an estrous cycle and requiring additional reproductive examinations or breeding attempts. If a stallion is affected, temporarily suspending breeding can disrupt services for multiple mares. ^[2]

Outbreaks may also result in additional costs for veterinary examinations, diagnostic testing, biosecurity measures, and monitoring exposed horses. Early recognition and control can reduce transmission and help limit the financial impact of an outbreak. ^[2]

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Management During an Outbreak

Early recognition of an ECE outbreak is important for proper management and containing the spread of infection. Once owners suspect ECE, they should take measures to reduce contact between affected horses and other breeding animals. Mares and stallions with suspected ECE should be removed from breeding while active lesions are present, which can disrupt breeding programs. ^[1][2][4]

Breeding should not resume until lesions have completely healed. Your veterinarian can help determine when it is appropriate for an affected horse to return to breeding. Giving the horse time away from breeding also prevents repeated irritation of painful, healing tissues. ^[1][4]

Horses that have recently bred with an affected mare or stallion may have been exposed to EHV-3. These horses should be monitored closely for genital lesions or swelling. Breeding should stop if suspicious lesions appear, and the horse should be evaluated by a veterinarian. Accurate breeding records can help identify which horses may have been exposed during an outbreak. ^[1][4]

Effective biosecurity measures can also help prevent the virus from spreading to other horses. ^[1][4][5]

Best practices to follow during an outbreak include: ^[1][4][5]

• Use dedicated equipment for affected horses when possible
• Wear disposable gloves when examining or handling genital areas
• Change gloves between horses
• Wash hands thoroughly after handling affected horses
• Clean and disinfect reusable reproductive equipment
• Avoid unnecessary contact between affected and unaffected breeding horses

These precautions help limit opportunities for direct and indirect transmission. When practical, handlers should care for unaffected horses before working with affected horses. ^[1][4][5]

Prevention

There is currently no commercially available vaccine specifically for EHV-3. Preventing ECE therefore depends mainly on breeding management, hygiene, and recognizing affected horses before they spread the virus. ^[1][4]

Do not breed a horse with suspicious genital lesions until the horse has been examined by a veterinarian.

Breeding examinations are an important part of preventing ECE. Check mares and stallions for unexplained sores, blisters, swelling, or other changes around the genital area before breeding. This precaution is crucial for natural breeding because direct genital contact is the primary route of EHV-3 transmission. ^[1][4][7]

Good hygiene during breeding and reproductive examinations can also reduce the risk of transferring EHV-3 between horses.

Important practices include: ^[1][4][5]

• Using clean reproductive equipment
• Cleaning and disinfecting reusable instruments
• Changing examination gloves between horses
• Washing hands after handling reproductive tissues
• Avoiding the transfer of contaminated materials between horses
• Using appropriate biosecurity practices when new breeding horses arrive

Together, these practices can also help reduce the spread of other infectious diseases between breeding horses.

Horses that have recovered from ECE may carry EHV-3 for life, even when they appear completely healthy. Owners should monitor previously affected horses for new genital lesions, particularly during breeding season. If suspicious lesions develop, stop breeding the horse and contact your veterinarian. ^[1]

A previous ECE infection does not necessarily mean a horse must be permanently removed from breeding. Careful monitoring and good breeding hygiene can help reduce the risk of transmission. ^[1]

Frequently Asked Questions

Here are some frequently asked questions about equine coital exanthema in horses:

Summary

Equine coital exanthema is an EHV-3 infection that causes painful genital lesions in breeding horses. Most horses recover well, but lifelong viral latency requires continued monitoring and careful breeding hygiene.

• ECE causes blisters and shallow ulcers on the vulva of mares or the penis and sheath of stallions
• The virus spreads mainly during breeding but can also be transmitted on contaminated equipment, gloves, or hands
• PCR testing of a fresh genital lesion can confirm EHV-3 infection
• Affected horses should stop breeding until lesions heal, with supportive care used to manage pain or secondary infection
• Most lesions heal within two to three weeks without affecting long-term fertility
• Recovered horses may carry EHV-3 for life, so ongoing monitoring, hygiene, and biosecurity are important