Equis ISSN 2398-2977

Ear: pinnal acanthosis

Synonym(s): Fungal plaques, ear fungus, aural warts, ear warts, ear papilloma

Contributor(s): Prof Derek Knottenbelt, David Senter

Introduction

  • A very common sometimes alarming complex skin lesion involving the skin of the inner surface of the pinna.  
  • Cause: papilloma virus unrelated to equine papilloma virus responsible for conventional warts.
  • Signs: individual or coalescent pink or gray papules on the skin of the pinna. Can be extensive and much larger areas involved.
  • A second form of the condition can be found on around the sheath and glabrous skin forward of umbilicus and more rarely still on the medial aspect of the thighs. 
  • Diagnosis: history, characteristic clinical appearance, biopsy. 
  • Treatment: benign neglect is recommended.   
  • Prognosis: good but most cases remain static or gradually improve or deteriorate. A few cases are severe and then can cause secondary effects in the ear canal itself.

Pathogenesis

Etiology

  • Distribution of lesions strongly suggestive of vector transmitted virus infection.  
  • Virus has been identified by both electron microscopy and PCR methods.  
  • Vector assumed to beSimuliumspp (black fly) bites because the pinna and ventral midline region forward of umbilicus and medial thighs are preferred biting sites.
  • Earliest lesions are often very small punctate depigmented skin changes that gradually expand due to epidermal hyperplasia.  
  • Insect bite reactions have been suggested but most have no evidence of this and the anatomical.

Predisposing factors

General
  • Most cases develop in the spring/summer but signs may be seen some weeks after onset.
  • Successive waves/crops of lesions may develop in individual horses.

Pathophysiology

  • Very marked thickening and even some ulceration and bleeding occasionally occur.
  • Virally induced epidermal hyperplasia and hyperkeratinization are suggested to be the main etiopathogenesis.
  • Intranuclear crystalline arrays of roughly hexagonal viral particles have been found consistently in samples from affected skin. Their appearance is typical for papilloma virus   Papilloma virus    the viruses themselves are not visually distinguishable from equine papilloma virus.  
  • Viral particles are located as expected in the stratum spinosum and stratum granulosum.  
  • The precise nature of the virus has not yet been established.
  • The location of the lesions suggests that direct trauma is an unlikely route of viral infection. More likely they are transmitted in some way by simulid flies whose preferred feeding sites are the common sites for the disease (inner pinna   Ear: papilloma 01    Ear: papilloma 02   and hairless skin of the ventrum, sheath and thighs).

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Fairley R A & Haines D M (1992) The electron microscopic and immunohistochemical demonstration of papillomavirus in equine aural ear plaquesVet Pathol 29, 79-81 PubMed.

Other sources of information

  • Scott D W & Miller W H (2003) Equine Dermatology. W B Saunders, USA. pp 701-703.
  • Pascoe R R & Knottenbelt D C (1999) Manual of Equine Dermatology. W B Saunders, UK.
  • Scott D W (1988) Large Animal Dermatology. W B Saunders, USA.


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