Equis ISSN 2398-2977

Papilloma virus

Synonym(s): EPV

Contributor(s): Sarah Binns, David Senter, Richard Walker




  • Family:Papovaviridae.
  • Subfamily:Papillomavirus.


  • L:papilla- nipple.
  • Gk:-oma- tumor, abnormal growth.

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Clinical Effects



  • Can survive on fomites, such as thorns, grooming brushes or surgical instruments.


  • Acquired through skin abrasions.
  • Direct infection through contact with an infected horse.
  • Indirect infection from contaminated fomites.
  • Occasionally transmitted through sexual activity.
  • Papillomaviruses causing aural plaques may possibly be transmitted by biting arthropods.

Pathological effects

  • Recovered horses usually develop complete, life-long immunity to the virus after 3-4 months.
  • Complement-fixing and neutralizing antibodies develop.
  • If warts persist, immune compromise should be suspected.
  • Causes equine squamous cell papilloma ('warts')   Papillomatosis  and aural plaques - benign proliferative cutaneous epithelial neoplasms.
  • Warts are most commonly recognized in horses 1-3 years old; aural plaques in horses over 1 year old.
  • The incubation period may be more than 2 months.
  • Papillomas originate in the stratum basale of the skin, commonly on the muzzle, nose and lip commissures.
  • Multiple warts usually form.
  • Warts usually regress spontaneously within 1-9 months.
  • Aural plaque lesions preferentially affect the inner surface of the pinna.
  • Aural plaques rarely regress spontaneously, but are usually asymptomatic.


Control via animal

  • Treatment for warts is often not indicated, unless for aesthetic reasons.
  • Few objective data on treatment of warts are available, but many treatments have been suggested.

Control via chemotherapies

  • Various therapies have been suggested for warts, including:
    • Intralesional or intravenous immunomodulatory mediators, eg Bacille de Calmette et Guerin (BCG).
    • Intralesional cisplatin.
    • Topical caustic agents.
    • Biological response modifier, eg 5% imiquimod cream.

Control via environment

  • Fly repellents or appropriate management to avoid fly irritation may be required for aural plaques.
  • Fly repellents to avoid irritation of aural plaques.

Other countermeasures

  • Other proposed treatments for warts   Papillomatosis  include:
    • Surgical removal.
    • Cryonecrosis.
    • Radiofrequency hyperthermia.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Johnson P J (1998) Dermatologic tumors (excluding sarcoids). Vet Clin North Am Equine Pract 14 (3), 625-658 PubMed.
  • Fairley R A & Haines D M (1992) The electron microscopic and immunohistochemical demonstration of a papillomavirus in equine aural plaques. Vet Pathol 29, 79-81 PubMed.
  • O'Banion M K, Reichmann M E & Sundberg J P (1986) Cloning and characterization of an equine cutaneous papillomavirus. Virology 152, 100-109.