Equine Herpesvirus 3

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Also Known As: Equine Coital Exanthema — ECE — Genital Horsepox — Equine Venereal Balanitis


Equine Herpesvirus 3 (EHV-3), a member of the large Herpesviridae family, causes the highly contagious viral venereal disease, equine coital exanthema (ECE), which causes genital lesions on both stallions and mares.


Sporadic cases occur worldwide.

ECE is transmitted primarily via coitus but has also been seen on foals feeding from dams affected, presumably transmitted by contact. An asymptomatic carrier state may occur in stallions.

Iatrogenic transmission via personnel and equipment is also possible.


Horses of breeding age are usually affected due to the mode of transmission.

Aged mares may develop recurrent ECE during gestation and the peri-parturient period.

Clinical Signs

ECE causes vesicular lesions on the penis and prepuce of stallions and vulva of mares which can be extrememly painful, especially to males. These lesions often suppress breeding behaviour but have no direct impact upon fertility.

The initial vesicles begin on the penis, spreading onto the prepuce and develop into pustules which then slough leaving ulcerated areas up to 1.5cm in diameter. These ulcers heal within a few weeks but leave depigmented scars behind. Systemic signs develop occasionally in stallions, affected animals exhibiting a dull, depressed demeanour and pyrexia.

In mares,small red nodules appear on the vulva, vaginal mucosa, clitoral sinuses and perineal skin 4-8 days after breeding. These develop into pustules and then vulval erosions which form scabs and then heal very similarly, leaving depigmented scars.

Ulcers can occasionally be found on the teats, lips, nasal and oral mucosae.

In cases with secondary Streptococcus spp. infection, the ulcers enlarge and exude a mucopurulent discharge.


Diagnosis is usually based upon clinical signs. Paired antibody titres can also be measured and interpreted with a 2-3 week interval.

The margins of ulcers can be viewed under electron microscopy revealing viral particles within the cells. Biopsies of lesions can also be histologically examined for viral inclusion bodies.


ECE resolves spontaneously within a few weeks, requiring no treatment. A short-lived immunity then develops. Recurrence within the same breeding season is uncommon.

Topical antibiotics may be used to prevent secondary infections while lesions are open and ulcerated.

Stallions should be rested while affected to prevent transmission, pain and association of pain with breeding which may lead to future breeding problems.


Affected stallions should be rested for at least 3 weeks after cessation of clinical signs to prevent spread to mares. Semen from such individuals may be collected and delivered via artificial insemination if permitted.

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Lavoie, J-P., Hinchcliff, K. W (2008) Blackwell’s Five-Minute Veterinary Consult: Equine 2nd ed. Wiley-Blackwell, Oxford, pp378-379.

Merck Veterinary Manual, Equine Coital Exanthema, accessed online 24/07/2011 at http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/110800.htm

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