Equis ISSN 2398-2977


Synonym(s): Warts, Equine viral papillomatosis, Grass warts, Milk warts, Fungal plaques, Cutaneous viral papilloma, Angleberry

Contributor(s): Clare Knottenbelt, Prof Derek Knottenbelt, Rosanna Marsella, Reginald Pascoe, Sue Paterson, David Senter


  • Congenital form occurs in newborn foals; usually single or few but can be extensive.
  • Viral papilloma is very common in young horses and less so in older or immunocompromised animals. Most cases occur in young weanlings or yearlings during their first season at grass, hence colloquial terms - Grass warts, milk warts.
  • Spontaneous remission is common but NOT invariable.  
  • Several different syndromes may relate to different variants of the virus or to different related and unrelated viruses. Aural plaques (pinnal acanthosis) is a common but poorly understood variant that is probably caused by some different viruses and transmitted by the biting flies and especially Simulium spp (Black Fly).  
  • Initial development in older horses is much less inclined to spontaneous remission.
  • There is no relationship in any form to the equine sarcoid Sarcoid. Immune response to viral papilloma is not protective or curative for sarcoid.
  • Cause: equine papilloma virus. Papilloma virus.
  • Signs: small, multiple pink or grey pedunculated lesions on muzzle, head and ears.
  • Diagnosis: history, clinical signs, biopsy.
  • Treatment: not usually necessary; excision if causing interference, eg with eating.
  • Prognosis: depends on type.



  • Equine papilloma virus is implicated.
  • Nine equine papillomaviruses have been reported, and more than one virus type can be present within the same lesion.  
  • Usually require some form of skin damage to infect the skin.

Predisposing factors


  • Age-related occurrence and implications for treatment and prognosis.

Pinnal acanthosis is a very difficult condition that should not be treated.


  • Onset over 24 weeks with some resolving lesions and some new lesions at first than gradually spontaneous resolution of the typical papilloma.
  • Atypical papilloma occurs in older horses, especially in the groin region. 
  • Pinnal acanthosis is a long-standing condition; most cases remain static for years and sometimes for life.


  • Horses on pastures with a history of being grazed by affected yearlings.
  • Moderately contagious by direct and indirect contact.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Barrelet A, Foote A & Littlewood J D (2010) Common equine skin tumours. UK Vet 15 (6), 9-17 VetMedResource.
  • Hibi H et al (2019) Laryngeal squamous cell carcinoma and papilloma associated with Equus caballus papillomavirus 2 in a horse. J Vet Med Sci 81 (7), 1029-1033 PMC.
  • Li C X et al (2019) Identification of a Novel Equine Papillomavirus in Semen from a Thoroughbred Stallion with a Penile Lesion. Viruses 11 (8), 713 PubMed.
  • Peters-Kennedy J et al (2019) Equus caballus papillomavirus 8 (EcPV8) associated with multiple viral plaques, viral papillomas, and squamous cell carcinoma in a horse. Equine Vet J 51 (4), 470-474 PubMed.
  • Mira J, Herman M et al (2018) Frequency of Equus caballus papillomavirus in equine aural plaques. J Vet Diag Invest 30 (4), 565-568 PubMed.
  • Sloet van Oldruitenborgh-Oosterbaan M M & Grinwis G C M (2018) Viral skin diseases in the Netherlands. Equine Vet Educ 30 (10), 558-563 VetMedResource.
  • Sykora S & Brandt S (2017) Papillomavirus infection and squamous cell carcinoma in horses. Vet J 223, 48-54 PubMed.
  • Torres S M F & Koch S N (2013) Papillomavirus-associated diseases. Vet Clin Equine 29 (3), 643-655 PubMed.
  • van den Top J G B, de Heer N, Klein W R & Ensink J M (2008) Penile and preputial tumours in the horse: A retrospective study of 114 affected horses. Equine Vet J 40 (6), 528-532 PubMed.
  • Pilsworth R C & Knottenbelt D (2007) Papillomatosis (viral warts). Equine Vet Educ 19 (8), 444-446 VetMedResource.

Other sources of information

  • Scott D W & Miller W H (2011) Neoplasms, Cysts, Hamartomas and Keratoses. In: Equine Dermatology. 2nd edn. Saunders, USA. pp 468-516.
  • Knottenbelt D C (2009) Viral Diseases. In: Pascoe’s Principles and Practice of Equine Dermatology. 2nd edn. Saunders, USA. pp 129-140.
  • Scott D W (2003) Neoplastic and Non-Neoplastic Tumors. In: Equine Dermatology. W B Saunders, Philadelphia, USA. pp 700-706.
  • Pascoe R R & Knottenbelt D C (1999) Manual of Equine Dermatology. W B Saunders, London.