Canine atopy is essentially another name for canine allergies. Most dogs with atopic dermatitis are triggered by environmental allergens, although some allergic reactions can be attributed to food allergies. The allergens causing your dog’s problems, as well as his reactions, are usually quite diverse.

Pets with atopy usually experience pruritis, or severe itching. Possible symptoms you may notice include licking of the paws, rubbing of the face and eyes, pruritis in the axille (under the front legs) in the groin, and chronic ear redness or ear infections. Often the atopy is concurrent with a flea allergy, during which the dog will chew between the rear legs, above the tail head and on the thighs. When experiencing food allergies, a dog will experience gastrointestinal problems.

Atopy may be a consequence of indoor, outdoor or food allergies, and is generally a combination of any of these. Outdoor allergies may be more seasonal; indoor and food allergies may show symptoms on a year-round basis. Environmental allergens may be specific for a certain part of the country; the native flora of one location, like the presence of certain grasses and pollens, may not be found in other areas. Tree pollens in the south, such as pine and pecan, will not be a common problem in Arizona where the weather is dry. Molds are a more common allergen in a moist area such as Louisiana, versus a dry environment like Nevada. In the United States most animals are multisensitive—they are allergic to more than one antigen. The most common allergens in Europe are house dust, house dust mites and human dander. Insect antigens, such as the mosquito and deer fly, cause allergic reactions in many atopic dogs. If a pet is moved from one part of the country to another, you may see a decrease in allergy symptoms due to a corresponding decrease of allergens in a particular area. But, as is unfortunately the case with an allergic individual, the beneficial effects of the move will be counteracted by the development of new allergies to allergens native to the new environment.

Interdermal skin testing is the best way to determine atopy-causing allergens that aren’t food-related. The test should be tailored to include common allergens in the part of the country in which you live. The test consists of injecting small amounts of allergen into the dermis of the skin and the observing and noting any subsequent allergic reaction. Reactions may include redness and swelling at the site of the injection. These reactions can occur immediately or be delayed. Have your pet checked 24 hours after an interdermal allergy test to check for a delayed reaction.

10 to 30% of atopic dogs may have negative skin test reactions. Common sources of interference with interdermal allergy testing include the taking of anti-inflammatory medications, or even medicated shampoos. Prior to allergy testing, injectable steroids should not be used for 2 months, oral and topical steroids should be withdrawn for 4 weeks, and antihistamines for 2 weeks. Products containing omega 3 and 6 fatty acids as well as medicated shampoos should be withdrawn 10 days prior to testing. Using any of these medications prior to testing may give you false results.

The best way to determine food allergies is to feed a diet that the pet has never been exposed to before. The most common food allergens include soy, egg, chicken or corn. Many dermatologists recommend a rabbit and potato as diet as their number one choice of a hypoallergenic diet. One of the most previously popular diets, lamb and rice, will often contain chicken, eggs and or preservatives, and is not considered truly hypoallergenic. Other hypoallergenic diets include white fish and potato, duck and potato, kangaroo and oats, and venison and potato. Venison and potato is a best seller, but is similar enough to beef to cause some cross-reactivity in dogs with beef allergies. These limited diets are marketed by Royal Canine, Eukuniba, and Hills. Another class of hypoallergenic diets consists of hydrolyzed proteins. Hydrolyzed proteins are proteins that are partially digested. In theory, long chain amino acids are more likely to produce an allergic reaction than are short chain amino acids. Hills produces a product called ZD, which is hydrolyzed chicken protein, and Purina manufactures a product called HA which contains hydrolyzed soy protein.

Regardless of the hypoallergenic diet chosen, a pet should be fed only that particular diet for a 6 week period of time to observe if there is a decrease in atopy symptoms. During the food trial, refrain from feeding any potential food antigens including doggy or people snacks. Even rawhide bones could be a potential source of allergens.

If the hypoallergenic diet improves the case of atopy after the 6 week diet trial, additional foods may be added to the diet slowly. For example, you may want to include baked chicken to the diet for 1-2 weeks. If no increase in pruritis is seen, you may safely assume that chicken was not an allergen responsible for this particular pet’s atopy.

Please note that allergies may change over time. A diet that is hypoallergenic for a 2-year-old dog may not remain effective for that pet 2-3 years later. The pet may develop allergies later to rabbit, potato, lamb or kangaroo. If clinical signs become worse a new diet trial may become necessary.

There are several ways to treat atopy, and all have varying degrees of success. First you can avoid what you are allergic to—often this is easier said than done. For example, if you were allergic to dust, you could vacuum and dust the home daily and yet not be able to escape the allergen entirely. A second way is to take the allergens you are allergic to and make a sterile extract of these allergens, thereby comprising an allergy serum which is injected into the patient in increasing amounts. This process is called hyposensitization therapy. An additional way of dealing with allergies is to decrease the allergic response through medication. Two drugs commonly used to cover up allergy symptoms are antihistamines and corticosteroids. Antihistamines block the release of histamines, released by the mast cells and causing an inflammatory response. Blocking histamines creates a decrease in redness, swelling and pruritis. Corticosteroids are often the most effective in eliminating allergic clinical signs, but will often result in a host of unpleasant side effects, including increased thirst and urination. Prolonged use of corticosteroids may result in thinning of the skin, liver enlargement, and heart problems. Cushing’s syndrome may be a result of protracted steroid usage.

Topical medications include medicated shampoos, sprays and powders. Often these products will also contain corticosteroids and antihistamines alone or in combination with sulfur, oatmeal, topical anesthetics and fatty acid emollients. Sulfur is very soothing to the skin, and a rinse or sulfur dip is very effective in the elimination of inflammation—unfortunately it has the unpleasant side effect of smelling like rotten eggs! Sulfur in smaller quantities if included in shampoos that help to mask the sulfur odor. You will often see sulfur combined with tar products to create a shampoo which is both soothing to the skin, and helps remove the excessive thickening and scaling (keratolytic) associated with irritated skin. Omega fatty acids are added for their skin-nourishing effects, and when supplemented with protein coat conditioners help increase manageability and give luster to the coat. Most topicals provide temporary relief of atopy but require frequent retreatment to be effective.

A relatively new immunotherapy may also be effective for canine atopy. Novartis Animal Health manufactures Atopica, cyclosporine capsules in various sizes to match the size of the dog. This is a nonsteroidal therapy which decreases the immune response to the allergen. Specifically Atopica is a T-lymphocyte immunosuppressor that will also inhibit eosinophil activation, thereby decreasing inflammation. Atopica is given at a dose of 5 mg/Kg daily until satisfactory results are obtained, usually 4 to 8 weeks. The dose of Atopica may then be decreased by dosing every other day, and eventually increasing the length of time between dosages unless clinical signs reappear. Administration of cyclosporine should not be within two hours of eating. The most common side effects of Atopica include diarrhea and vomiting although more severe reactions have been reported.




References:

Muller and Kirk, “Small Animal Dermatology” 5th Edition. W.B. Saunders Co. Philadelphia. Pp.500-518.

Hilary A. Jackson, “Dermatologic Manifestations and Nutritional Management of Adverse Food Reactions”. Veterinary Medicine. Vol 102. No. 1. January 2007.