Canis ISSN: 2398-2942

Skin: allergic contact dermatitis

Synonym(s): Contact hypersensitivity

Contributor(s): Rosanna Marsella, David Scarff

Introduction

  • Rare, delayed or cell-mediated hypersensitivity reaction to contacted allergens in sensitized individuals.
  • Cause: various allergens.
  • Signs: alopecia, erythema, papular eruption.
  • Diagnosis: history, clinical signs (resolution with avoidance/confinement), histopathology, patch test.
  • Treatment: glucocorticoids, bathing, and removal of allergen.
  • Prognosis: good if allergen identified.

Pathogenesis

Etiology

  • Compounds are simple, acting as haptens to link epidermal proteins.
  • Plant resins and oils.
  • Medications, eg neomycin in otic preparations, for containing shampoos.
  • Carpet mordants and dyes.
  • Chlorine in water.
  • Flea collars.
  • Insecticides.
  • Plastic feed bowls.
  • Plants (Commelinanceaefamily).

Pathophysiology

  • Chemicals act as haptens to bind to proteins, forming a conjugate which binds to Langerhans' cells in the skin. These altered cells trigger a T-cell response.
  • Following exposure to antigen in a sensitized animal, mononuclear cells infiltrate the skin and then are removed by sensitized lymphocytes leaving intra-epidermal vesicles.
  • This type IV hypersensitivity reaction leads to pruritus.
  • Low molecular weight haptens link epidermal proteins to form antigens. Antigen is trapped, processed and presented by Langerhans' cells. They produce cytokines which attract T-cells → activation of keratinocytes to release pro-inflammatory cytokines. They also travel to local lymph nodes to amplify the immune response.

Timecourse

  • Sensitization takes a minimum of 6 months.
  • After contact with an allergen, clinical signs will take 48 h to develop in a sensitized dog. This is a delayed allergic reaction.

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.
  • Marsella R et al (1997) Use of pentoxifylline in the treatment of allergic contact reactions to plants of the Commelinanceae family in dogs. Vet Derm 8 (2), 121-126 Wiley Online Library.
  • Walder E J & Conroys J D (1994) Contact dermatitis in dogs and cats - pathogenesis, histopathology, experimetal induction and case reports. Vet Derm 5 (4), 149-162 VetMedResource.
  • Olivry T, Prélaud P, Héripret D & Atleer B A (1990) Allergic contact dermatitis in the dog - principles and diagnosis. Vet Clin North Am 20 (6), 1443-1456 PubMed.
  • Kunkle G A (1988) Contact dermatitis. Vet Clin North Am 18 (5), 1061-1068 PubMed.


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