Atopy, Predisposition to Allergic Diseases
Atopic dermatitis is the predisposition to allergic disease in response to environmental allergens. One of the most common source of allergens causing atopy is the house dust mite. Tree, grass and weed pollens can also cause this disease. Flea allergic dermatitis and parasitic infections such as sarcoptic mange (scabies) and otodectic mange also cause allergic-type reactions.
Atopic dermatitis, the second most common hypersensitivity in dogs and cats, is a common, genetically programmed, itchy disease of dogs and cats. The sensitizing antigen is generally an inhaled environmental allergen.
Atopic Dermatitis in Dogs
Females tend to more affected than males. Though any breed can develop atopy, several breeds have a marked predisposition including Cairn Terrier, West Highland White Terrier, Shar-Pei, Scottish Terrier, Lhasa Apso, Wirehaired Fox Terrier, Dalmatian, Irish Setter, Boston Terrier, Pug, Golden Retriever, Boxer, English Setter, Labrador Retriever, and Miniature Schnauzer. The onset usually occurs 1-3 years of age, with the exception of the Shar pei which can begin as young as 3 months.
Signs of Atopic Dermatitis in Dogs
Dogs with atopic dermatitis usually have physical signs commonly seen in other dog skin diseases, such as flea bite hypersensitivity, food hypersensitivity, contact dermatitis, scabies, intestinal parasite hypersensitivity, folliculitis, pelodera dermatitis, and hookworm dermatitis. In cats atopic dermatitis often mimics various causes of symmetric alopecia, indolent ulcer, eosinophilic plaque and eosinophilic granuloma.
Atopic Dermatitis in Cats
Felines show no breed or sex predilection.
Primary skin lesions, in the absence of secondary infections, are not commonly seen. Skin lesions seen in atopic animals are usually associated with self-trauma, secondary pus-forming bacterial infection (pyoderma), and secondary seborrheic skin disease. The lesions are generally found on the face, feet, and abdomen. Chronic inflammation and pruritis produces variable degrees of hyperpigmentation, formation of purplish plaque, alopecia, and salivary staining, and itchiness.
-
Crusted red spots affecting the ear flaps, outer aspect of elbows and hindlimbs with intense itchiness, sometimes with family members affected, is typical of sarcoptic mange. Itching with hair loss, crusting and scaling affecting the lower part of the back and tail base, often with sudden spinning round to nibble, is indicative of flea allergy dermatitis.
-
Foot licking, recurrent ear inflammation, face rubbing, itching of the armpits and groin in a young animal is very suggestive of atopy.
These clinical signs initially seasonal or non-seasonal depending on allergen. Most animals with seasonal allergies tend to develop non-seasonal allergies.
Signs of Atopic Dermatitis in Cats
Facial itchiness with or without lesions (2); itchy ears with or without lesions (3) widespread itchy crusts and papules (miliary dermatitis) (4) ulcers, eosinophilic plaque or eosinophilic granuloma (5) symmetric alopecia and (6) generalized itch with or without lesions.
Diagnosis of Atopic Dermatitis
Diagnosis of allergies is a complicated task. The investigation of a suspected allergic dog should include rigorous treatment for external parasites and secondary bacterial and yeast infections which often complicate and contribute to the itch. A diagnosis of food intolerance is made in 2-10% of 'itchy' dogs. It can be controlled without using drugs and is worth ruling out by introducing an elimination diet followed by dietary challenge to confirm the diagnosis. Elimination diets are time consuming and require considerable owner commitment. It can be up to 3 months before the dog stops scratching. Once other causes of itch have been ruled out, specific tests to detect allergic antibodies to environmental allergens can be undertaken to confirm the diagnosis of atopy.
Skin tests can be used to determine the allergens to which the animal is hypersensitive. It is essential to understand that a positive skin test means only that the patient has skin sensitizing antibodies, not necessarily a clinical allergy. False results can often occur.
Reasons for false positives include: (1) irritant test allergens (2) bacterial or fungal contaminated test allergens (3) skin sensitizing antibody only (4) poor technique (5) substance causes non-immunogenic histamine release (6) "irritable" skin.
Treatment of Atopic Dermatitis
Unfortunately, dogs rarely 'grow out' of their allergies and most atopic dogs require lifelong therapy. Various treatments are available and your veterinary surgeon will recommend the best regime. Unfortunately, many atopic dogs are prone to recurrent secondary bacterial and yeast infections which will require intermittent or ongoing therapy as well as treatment to control the underlying allergic disease. An atopic dog can be difficult to treat and expensive.
Affected animals should not be used for breeding. The breeders of atopic animals should be informed if a particular sire and dam produced affected offspring and this should influence decisions regarding future breeding.
References:
REF FILE #DH-128-67
|