Reproduction: coital exanthema - EHV 3 in Horses (Equis) | Vetlexicon
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Reproduction: coital exanthema – EHV 3

ISSN 2398-2977

Synonym(s): Genital horse pox, eruptive venereal disease, equine venereal vulvitis/balanitis, coital vesicular exanthema


  • Coital exanthema is a highly contagious disease of the external genitalia primarily regarded as venereally transmitted.
  • Cause: equine herpesvirus-3 (EHV-3).
  • Signs: vesicles, pustules and ulcers on external genitalia; systemic signs occur rarely in stallions.
  • Diagnosis: lesions, virus detection, serology.
  • Treatment: self-limiting; prevent secondary bacterial infection.
  • Prognosis: good.
Print off the Owner factsheet on Equine herpesvirus - EHV to give to your clients.

Presenting signs

  • Vesicles, pustules, ulcers on external genitalia of mares or stallions.
  • Subclinical, latent infection in mares.
  • Systemic signs in stallion, eg anorexia, fever, lack of libido.
  • Reduced conception rates (very rare).

Acute presentation

  • As above.

Geographic incidence

  • USA, Canada, Australia, UK.
  • Worldwide.

Age predisposition

  • Adults.
  • Under 2 years (rare).

Breed/Species predisposition

  • None, but most likely in breeding animals.

Cost considerations

  • Temporary reduction in fertility due to delay in/or resistance to covering by stallion/mare.
  • Disruption of breeding schedule.



Predisposing factors

  • Mare or stallion involved in breeding.
  • Venereal contact at coitus.


  • Other transmitters include insects, veterinary surgeons/grooms, instruments, ultrasound probe.
  • Damage to the vulva from foaling injuries or surgery may encourage infection.


  • Equine herpesvirus-3 infection   →   venereal transmission   →   lesions on external genitalia.
  • Viral replication in stratified epithelium of epidermal tissue within skin or at mucocutaneous margins.
  • Highly contagious.
  • Non-venereally transmitted form recognized in maiden fillies and colts.
  • Hypothesized that latent infection is established in sciatic and/or sacral ganglion.
  • Venereal infection with EHV-3   →   stallions may rarely show systemic signs, eg dullness, anorexia, pyrexia.
  • Lesions (papules or nodules) up to 2 mm diameter develop first on penis, then prepuce 2-5 days later   →   vesicles up to 1.5 cm diameter   →   circumscribed pustules with raised border   →   slough and ulcerate (3-10 mm in diameter)   →   heal over 10-14 days by granulation leaving depigmented spots. Penis and prepuce may be painful and edematous.
  • Some affected stallions refuse to breed.
  • Recurrent cases can occur; recrudescence can also be seen after foaling.
  • Secondary bacterial infection delays healing and increases inflammation/pain.


  • Rarely show systemic signs.
  • Vulvar mucosal and perineal skin lesions   →   multiple discrete circular nodules (2 mm diameter) progressing to vesicles/pustules which rupture to scabrous erosions   →   hyperemic erosions with sharply defined margins   →   heal over 10-14 days unless complicated by secondary bacterial infection.
  • Secondary bacterial infection withStreptococcus zooepidemicus  Streptococcus spp  is common.
  • Signs include vulval discharge, tail switching, increased frequency of urination and arching of back.
  • Lesions around the anus can be associated with anorectal lymphadenopathy, constipation and tenesmus.
  • Delayed foaling or reduced pregnancy rates may occur due to missed breeding opportunities.
  • Rarely may cause reduced conception rates for that particular mating.
  • Some mares show recurrence of lesions, usually around the time of parturition.

Maiden fillies and colts

  • Non-venereal spread from infectious in-contacts.
  • Pyrexia and painful coalescing skin lesions over the anus and vulva in fillies, and perineum, scrotum and inside hindlimbs in colts.


  • Reinfection without clinical signs is common.
  • Virus may remain latent in genitalia.
  • Use of corticosteroids has caused recrudescence experimentally.


  • Incubation period 5-10 days.
  • Unless complicated the lesions granulate and heal within 2-3 weeks leaving depigmented circular lesions.
  • Covering can begin during the next estrus.


  • EHV-3 usually passed from subclinically infected mare   →   stallion at breeding   →   transmitted to susceptible mares prior to developing clinical signs.


Presenting problems

Client history

  • Contact with infected mare or stallion.
  • Breeding animal.
  • Lesions on external genitalia.
  • Reluctance to copulate, especially in stallion.
  • Reduced conception rates in usually fertile mares for one estrus.
  • Systemic illness.

Clinical signs

  • Vesicles, pustules and ulcers on penis and prepuce or vulva.
  • Pain and edema of penis and prepuce/perineal skin.
  • Depigmented circular lesions in similar areas following healing.
  • Secondary bacterial infection leads to increased purulent discharge and inflammation with delayed healing.
  • In stallion:
    • Reluctance to copulate.
    • Depression.
    • Anorexia.
    • Pyrexia.
  • Rarely lesions in mouth/nostril or lips due to genitonasal contact.
  • Sometimes lesions in rectum and around anus if recal examination gloves are not discarded between examination of individual mares.
  • Atypical manifestation of rhinitis due to iatrogenic spread from contaminated endoscope has been reported.

Diagnostic investigation



  • Complement fixing antibodies peak 14-21 days after infection, becoming non-detectable in 60 days.
  • Serum neutralizing antibodies peak 14-21 days after infection and remain for at least a year.
  • Identification of EHV-3 by demonstration of inclusion bodies in lesions.
  • Skin biopsy   Dermatology: biopsy  of lesions.


  • Microscopy: Herpesvirus particles identified by electron microscopy.

Confirmation of diagnosis

Discriminatory diagnostic features

  • History.
  • Clinical signs.

Definitive diagnostic features

  • Virology.
  • Serology.
  • Microscopy.
  • Histopathology.

Histopathology findings

  • Hyperplastic superficial and deep perivascular dermatitis with ballooning degeneration and eosinophilic intranuclear inclusion bodies.

Differential diagnosis


Initial symptomatic treatment

  • The disease is self-limiting.
  • Apply local antiseptic or antibiotic treatment   Therapeutics: antimicrobials  to prevent secondary bacterial infection (3-7 days).
  • Cleanse penis and prepuce with mild soap and water.

Corticosteroid creams are generally contraindicated, although recommended by some authors to reduce inflammatory response.

  • Sexual rest and daily cleaning of affected areas until no fresh lesions are seen.
  • Use of topical antivirals (aciclovir cream   Aciclovir  ) has been described.


  • Clinical signs.
  • Serology.

Subsequent management


  • Sexual rest for a minimum of 4 weeks.
  • Self-limiting disease, therefore prolonged treatment is not necessary.


  • Resolution of clinical signs.



  • Avoid iatrogenic transmission via contaminated sleeves, water or equipment.
  • Do not breed acutely affected animals.
  • Leave until next estrous period.


  • No available vaccination.
  • Routinely inspect breeding mares and stallions prior to mating.

Group eradication

  • Serology and epidemiologic data may be used to identify carrier mares.
  • All mares covered by an affected stallion during the previous 10 days should be examined, and treated if necessary.
  • It may be thought necessary to avoid breeding affected stallions for 10-14 days. Artificial insemination   Reproduction: artificial insemination  may be used once lesions are no longer painful.
  • Equipment should be cleaned and sterilized between mares or disposable instruments used.



  • The disease is self-limiting.
  • Pregnancy rates are normal in mares that do not become infected after breeding, or after clinical recovery.
  • Prognosis is good to excellent for clinical recovery, although some mares and (more rarely) stallions may show recurrent coital exanthema.

Expected response to treatment

  • Lesions typically heal 10-14 days after onset.
  • Virus may be shed for 40 days after acute infection, and repeat periods of shedding may occur.

Reasons for treatment failure

  • Latent genital infection may occur.
  • Recurrence occurs in some cases.
  • Natural immunity short-lived.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Barrandeguy M & Thiry E (2012) Equine coital examthema and its potential economic implications for the equine industry. Vet J 191 (1), 35-40 PubMed.
  • Barrandeguy M et al (2010) Outbreak or rhinitis caused by equine herpesvirus type 3. Vet Rec 166 (6), 178 PubMed.
  • Barrandeguy M et al (2008) Experimental reactivation of equine herpesvirus-3 following corticosteroid treatment. Equine Vet J 40 (6), 593-595 PubMed.
  • Blanchard T L, Kenney R M & Timoney P J (1992) Venereal disease. Vet Clin North Am Equine Pract (1), 191-193 PubMed.
  • Uppal P K et al (1989) Equine coital exanthema (EHV-3 virus) infection in India. Zentrabl Veterinarmed [B] 36 (10), 786-788 PubMed.
  • Pascoe R R (1981) The effect of equine coital exanthema on the fertility of mares covered by stallions exhibiting the clinical disease. Aust Vet J 57 (3), 111-114 PubMed.
  • Feilen C P, Walker S T & Studdert M J (1979) Equine herpesvirus type 3 (Equine coital exanthema) in New South Wales. Aust Vet J 55 (19), 443-444 PubMed.
  • Pascoe R R & Bagust T J (1975) Coital exanthema in stallions. J Reprod Fertil Suppl Oct (23), 147-150 PubMed.
  • Bitsch V (1972) Cases of equine coital exanthema in Denmark. Acta Vet Scand 13 (2), 281-283 PubMed.
  • Gibbs E P, Roberts M C & Morris J M (1972) Equine coital exanthema in the United Kingdom. Equine Vet J 4 (2), 74-80 PubMed.

Other sources of information

  • Horserace Betting Levy Board (2016) Codes of Practice. 5th Floor, 21 Bloomsbury Street, London WC1B 3HF, UK. Tel: +44 (0)207 333 0043; Fax: +44 (0)207 333 0041; Email:; Website: