Equis ISSN 2398-2977

Skin: contact dermatitis

Synonym(s): Contact allergy

Contributor(s): Rosanna Marsella, David Senter

Introduction

  • Although only few publications exist on contact dermatitis in horses, this disease is recognized by clinicians in the field.
  • Contact dermatitis may be irritant or allergic in nature.
  • Irritant reactions are noted in all exposed animals and are detectable the first time of exposure, while allergic reactions develop in a small number of animals and are not noticeable when animal is first exposed as hypersensitivity requires time to develop.
  • Cause: direct contact between the horses skin and an irritant substance, eg shampoo, fly spray, etc.
  • Signs: pruritus, scaling, alopecia.
  • Diagnosis: confinement, patch testing, biopsy.
  • Treatment: avoidance, anti-inflammatory drugs.
  • Prognosis: good.

Pathogenesis

Etiology

  • Small proteins (called haptens).
  • Substances reported to cause contact allergy include plants, bedding, shampoos, blankets, fly sprays   Skin: contact dermatitis 01    Skin: contact dermatitis 02  , topical antibiotics such as neomycin   Neomycin  .

Predisposing factors

General
  • Previous trauma to the skin, whether related to other pruritic conditions or the development of secondary infections, may predispose to increase allergen penetration thus the development of a hypersensitivity.

Pathophysiology

  • Contact hypersensitivity is a type IV hypersensitivity in which small allergens (haptens) are thought to bind to epidermal proteins in order to become a complete antigen. 
  • During the sensitization phase the allergen is processed by antigen presenting cells (Langerhan's cells) and presented to lymphocytes in regional lymph nodes. This phase can last from weeks to months and during this time no clinical signs are noted upon exposure.
  • Once sensitization has occurred any subsequent exposure to the allergen triggers release of pro-inflammatory cytokines, eg TNF-a, and activated memory T-cells are recruited at the site of the challenge.

Timecourse

  • Incubation (also called sensitization phase) varies from a few weeks to several months.
  • In some cases animals might have been exposed to allergen for up to years before developing any problem.

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.
  • Fadok V A (1995)Overview of equine pruritus.Vet Clin North Am Equine Pract11(1), 1-10 PubMed.


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