Atopy can be considered the canine equivalent of hay fever. It is quite common, affecting around 10 per cent of dogs. Animals with this condition become sensitized to substances (allergens) in the environment, that are inhaled or absorbed through the skin (and which cause no problems for non-atopic animals). The resultant allergic reaction is primarily seen as extreme itchiness (pruritis).
The main allergens involved are house dust mites, house dust, human dander, feathers, molds, and pollens from trees, weeds, and grasses. Atopic dogs are also prone to seborrhea, secondary bacterial skin infections (pyoderma) and probably yeast (Malassezia) infections as well
The exact mode of inheritance is unknown. There is a strong breed predilection for this condition, and marked familial involvement (ie. if both parents are allergic, there is a very strong likelihood the offspring will be as well).
The condition is usually first seen between 1 and 3 years of age, although it may develop as late as 6 or 7. Initially atopy may be seasonal (eg. from spring to fall) but most affected dogs eventually have signs all year round.
Dogs with atopy are very itchy. The areas most affected are the face, paws, lower legs, groin, and, less often, the ears and eyes. In addition to scratching themselves with their hind feet, they often lick or chew the affected areas, or rub along the carpet to scratch the face or ears. The intense itching can make them irritable and less tolerant of being handled.
Initially, there are no apparent skin abnormalities, except possibly slight reddening, even though the dog is clearly itchy. (This is important because in other conditions there is often a rash or some visible lesion.) Over time, lesions develop as a result of the scratching and self-trauma, bacterial or yeast infections, and seborrhea, all of which can contribute to the objectionable odor of these dogs. The skin becomes reddened and eventually darkened (hyperpigmentation), abraded, thickened, and wrinkled, with loss of hair and bronze staining from saliva.
The concept of "allergen load" is important in understanding and treating this disorder. Atopic dogs are generally allergic to more than 1 agent. A small amount of allergens may be tolerated without developing a reaction, but an increase in any one of those (ie. an increase in allergen load such as occurs during pollen season) may push your dog over the edge to an allergic reaction of extreme discomfort.
There are many skin diseases that cause itching, and they can all look rather similar on physical examination. Your veterinarian will ask you questions about your dog's diet, environment, any kind of skin care you are already providing, whether any other pets or people in the house are itchy, where and how quickly did the skin lesions start, and is there any seasonal pattern to the itching. The answers, as well as the age and breed of your dog, will provide diagnostic clues. For example, itching that begins suddenly and rapidly gets worse, is more typical of a flea allergy, scabies, or a drug hypersensitivity. Itching that begins insidiously and gradually worsens, is seen more often with atopy, food allergy, bacterial or yeast skin infection, and seborrhea. Skin infections and seborrhea commonly develop secondary to atopy and may have to be cleared up before your veterinarian can diagnose atopy.
Diagnostic tests may include multiple skin scrapings and smears (for mites or yeast infection), fecal examination (for parasites), skin biopsy, skin testing (for allergies to different substances), elimination diets or change in environment (if food or contact allergy is suspected),
Atopy can be satisfactorily controlled in at least 90 percent of affected dogs. There are 3 components to successful treatment, which will be life-long and will likely require modification from time to time. A combination approach is generally most effective.
1 reduction in exposure to allergens. This requires identification of the substances to which your dog is sensitive (ie. allergy testing). You may be able to avoid some allergens altogether (if your dog is allergic to feathers or tobacco smoke for example), and reduce exposure to others (by keeping your pet out of carpeted areas to reduce house dust mite exposure for example). Your veterinarian will discuss this with you, in conjunction with the results of your dog's allergy testing.
2 hyposensitization (immunotherapy or "allergy shots"). This is recommended when the allergens involved can't be avoided, and your dog has clinical signs more than 4 to 6 months of the year which can not be kept under control with medical therapy. Immunotherapy is carried out after your dog's allergens have been identified by allergy testing. Injections of low doses of the appropriate allergens are given at short intervals at first, and then boosters given as needed when clinical signs begin to reappear.
3 medical treatment. Long term management may include gentle moisturizing anti-pruritic (control itching) shampoos, fatty acids, antihistamines (more likely effective when given as preventative), and short-acting corticosteroids on alternate days (given for short periods at times when there are flare-ups, to mimimize the potentially serious side-effects).
A tentative diagnosis can be made based on history, physical exam, and laboratory tests to rule out other possibilities. Intradermal testing (and to a lesser extent, serologic allergy testing) is necessary for definitive diagnosis and identification of allergens involved. Diagnosis should not be made based solely on intradermal (because of low specificity) or serologic testing (very common false-positive reactions).
Intradermal testing is the preferred method of diagnosing canine atopy and determining appropriate immunotherapy. However to get good results requires experience, practice, and close attention to detail. Many factors can lead to false-positive and false-negative reactions. Where possible, it is desirable to refer cases to specialists in this area.
Although the specific mode of inheritance is unknown, it is best not to breed affected dogs, their parents, and preferably their siblings as well, given the strong familial predisposition to this condition.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Scott, D.W., Miller, W.H., Griffin, C.E. 1995. Immunologic Skin Diseases. In Muller and Kirk's Small Animal Dermatology. p. 500-518. W.B. Saunders Co., Toronto. This reference contains detailed information on allergy testing and on hyposensitization. Page 515 has practical suggestions for environmental management in atopic dogs.
Ihrke, P.J. 1995. Pruritis. In E.J. Ettinger and E.C. Feldman (eds.). Textbook of Veterinary Internal Medicine, pp. 214-219. W.B. Saunders Co., Toronto.
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