Equis ISSN 2398-2977

Reproduction: coital exanthema - EHV 3

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

Contributor(s): Sarah Binns, Terry Blanchard, Rachael Conwell, Graham Munroe, Sarah Stoneham


  • 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.



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.


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

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: enquiries@hblb.org.uk; Website: http://codes.hblb.org.uk.