Felis ISSN 2398-2950

Skin: allergic disease overview

Contributor(s): David Godfrey, Rosanna Marsella

Introduction

  • Although the hallmark of allergy is pruritus, this is not always readily apparent in cats.
  • Signs: very variable   →   excoriation, miliary dermatitis, alopecia and eosinophilic granuloma complex disorders are all common.
  • Allergens may be derived from ectoparasites, airborne particles, drugs and chemical, ingested substances and possibly some other sources.
  • Diagnosis: often by trial treatment although ancillary diagnostic tests area important.
  • Treatment: pharmaceuticals: ectoparasiticides and anti-inflammatories, with avoidance of the allergen rarely being possible.
  • Prognosis: guarded for cure - most cats require on-going therapy.

Pathogenesis

Etiology

  • Flea allergic dermatitis Flea bite hypersensitivity Dermatitis: flea allergic  Flea feces test  Flea feces: microscopic appearance :
    • the allergen is substances found in flea saliva.
  • Food allergy Food hypersensitivity Food allergy testing  Skin: food allergy 01  Skin: food allergy 02  Skin: food allergy 03 :
    • This condition may be a mixture of true allergic disease and the ingestion of excessive amounts of pruritus-inducing substances, eg histamine.
  • Atopy Skin: atopic dermatitis  Atopy: positive intradermal skin test :
    • Probably a Type I hypersensitivity to air-borne allergens either inhaled or entering the body percutaneously.
  • Drug reactions Drug eruption  Drug eruption: due to FeLV vaccination :
    • Part of the pathogenesis in reactions to drugs and vaccines can be hypersensitivities.
  • Contact allergy Skin: allergic contact dermatitis  Allergic contact dermatitis :
    • Is not well documented in cats.
  • Insect bite hypersensitivity:
    • Well documented to occur with mosquito bites.
  • Angiedema:
    • Usually caused by hymenoptera stings, also reported with flea and drug allergens.
  • Urticaria:
    • Probably reported with drugs.
  • Ectoparasites Parasitic skin disease: overview:
    • Although these are often usually classified as etiologically different from allergy, the pathogenesis of parasitic dermatoses often involves allergic disease, eg infestation with Otodectes cynotis Otodectes cynotis.
    • An allergic reaction may occur in those cats which are pruritic with dermatophytosis   Dermatophytosis.
  • Miscellaneous:
    • Allergies to intestinal worms and protozoa, and to anal sac material have been postulated but little has been reported about these purported conditions.

Pathophysiology

  • Allergic skin disease is the subject of much of the research in veterinary dermatology although relatively little is directed at feline disease.
  • Different pathological processes are involved in different allergic conditions and there is probably always a mixture of processes in any one condition.

Coomb's classifications

Current concepts

  • Some more recent ideas about the pathogenesis of allergies include the concept of the balance among CD4 helper T cells being awry, such that the T helper 2 cells are more active than in a non-allergic individual.
  • Cytokines, especially interleukin-4, induce excessive IgE.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • O'Dair H A & Foster A P (1995) Focal and generalized alopecia. Vet Clin North Am Small Anim Pract 25 (4), 851-870 PubMed.
  • Wills J & Harvey R (1994) Diagnosis and management of food allergy and intolerance in dogs and cats. Aust Vet J 71 (10), 322-326 PubMed.
  • Scott D W, Miller W H Jr. (1993) Medical management of allergic pruritus in the cat, with emphasis on feline atopy. J S Afr Vet Assoc 64 (2), 103-108 PubMed.
  • Miller W H Jr. (1989) Nutritional considerations in small animal dermatology. Vet Clin North Am Small Anim Pract 19 (3), 497-511 PubMed.
  • Schultz K T (1982) Type I and type IV hypersensitivity in animals. JAVMA 181 (10), 1083-1087 PubMed.
  • Thoday K L (1981) Investigative techniques in small animal clinical dermatology. Br Vet J 137 (2), 133-154 PubMed.
  • Scott D W (1978) Immunologic skin disorders in the dog and cat. Vet Clin North Am (4), 641-664 PubMed.

Other sources of information

  • Bevier D E (1997) Atopy. In: Consultations in Feline Internal Medicine. pp 214-220. 3rd edn. Ed. August J R. W B Saunders. ISBN 0 7216 5814 8.
  • Scott D W, Miller W H and Griffin C E (1995) Hypersensitivity disorders. In: Small Animal Dermatology. pp 497-556. 5th edn. ISBN 0 7216 4850 9.
  • Moriello K A (1994) Allergic skin diseases. In: The Cat - diseases and clinical management. pp 1924-1931. 2nd edn. Ed. Sherding R G. W B Saunders. ISBN 0 443 08879 9.


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