Allergic Dermatitis

by Bruce W. Little, DVM

ALLERGIC DERMATITIS


We have written in this space previously about itchy skin on the family dog with incessant scratching, hair loss and severe burning discomfort whereby the dog awakens family members at night seeking relief from this most uncomfortable condition. In previous articles, we talked about the physical irritation and self-mutilation of dogs who were experiencing some form of skin irritation due to fleas crawling over their skin, ticks biting to have a blood meal, mange mites boring into the skin causing itching and discomfort, or ear mites irritating the dog’s ear canals causing severe scratching, head-shaking and further skin irritation. Although these primarily physical irritations can lead to allergic dermatitis, they don’t always do so. There are over 160 skin conditions that affect dogs. Some of these conditions are treatable and can be resolved with a successful cure, while others are of a more chronic nature and must be monitored and controlled with selected diets, medications, supplements, shampoos and other skin treatment products over a long period. Your veterinarian needs to gather a complete history of the symptoms that were observed leading up to the incessant scratching and biting of body parts. Severe scratching due to external parasites or self-induced body sores and inflammations can usually be cured or controlled by utilizing one of many parasite control insecticides and soothing shampoo and rinses to control the parasite population that is causing the problem.

Unlike human cases of allergies which usually manifests itself as an upper respiratory condition with runny noses, itching and watering eyes and stuffed up heads, allergic dermatitis in dogs creates a skin problem causing itchy, dry skin and causing incessant scratching by the dog. This continuous scratching can lead to further sores and inflamed skin that exacerbates the uncontrollable scratching therefore leading to even further skin irritation. In this article, we will limit our discussion to allergic dermatitis that exhibits clinical signs caused by three common irritants to which your dog may be susceptible. Those conditions, some of which, seem to show their clinical signs in the late summer or fall of the year are: flea bite dermatitis, atopic dermatitis and food allergy dermatitis. All three can cause severe itching and scratching leading to serious skin irritations for the dog. The most common cause of allergic dermatitis in dogs is flea bite dermatitis. When the flea bites, it secrets a protein through its mouthparts that prevents the blood from coagulating so they can extract a blood meal. Many dogs develop a reaction to this protein which can cause a severe allergic dermatitis. A flea infestation with just a few fleas can cause scratching by the dog to the extent that the dog causes self-inflicted skin rash or irritation. Sometimes, if left untreated, these irritations become infected causing major sores usually on the rump area. Other signs of flea-bite dermatitis include fever, loss of appetite and incessant scratching that leads to further skin damage. To control the flea population a vigorous management process must be put in place on the dog, in the house and in the yard or any other location that the dog may frequent. New and safer more effective products aimed at controlling fleas have made flea management possible without pesticide sprays, shampoos and dusts in most situations. Once fleas infest a home, control will require a vigilant program that includes vacuuming, eliminating fleas on pets, and cleaning and treating areas outdoors where pets frequent. If yours is a multi-pet family, you must control the flea infestation on all pets to control the flea bite dermatitis on the effected dog. Newer products to control fleas on dogs are applied either orally or topically to the body and are much more effective than the products that were available even a few years ago. Veterinarians can now prescribe products to help manage flea allergies by using products that kill the fleas before they accumulate enough protein in their saliva to cause an allergic reaction. It is important to consult with your veterinarian about total management of the flea population when attempting to treat flea bite dermatitis on your family dog.

Canine atopic dermatitis is a common, genetically related, inflammatory and pruritic (itchy) skin disease found in dogs. It is thought to be an inherited condition that is related to the immune system; therefore, there is a wide disparity in clinical signs necessary for diagnosing the exact cause and developing a specific treatment regimen for controlling the condition. Different breeds of dogs and various geographical locations may cause the signs of atopic dermatitis to vary considerably from other cases in the same environment. It is extremely important for the veterinarian to capture a comprehensive history from the family members regarding the dog’s daily lifestyle. Does the dog stay inside all the time except for walks on a leash to go to the bathroom, or is it allowed to roam free from the in-home environment? Does the dog frequent wooded areas or is it confined to the owner’s yard or immediate surroundings? What does the dog eat including treats and occasional raids on the garbage cans in the kitchen or elsewhere? The veterinarian must first rule out other skin conditions that may have clinical signs that resemble or overlap with canine atopic dermatitis. The variation in breed predilection or genetic factors, the stage of the disease, the presence of secondary infections, as well as resemblances to other non-atopic related skin diseases, must be confirmed before a differential diagnosis can be assured. Finally, after a complete history of the dog’s daily routine, food consumption, environmental factors such as parasite infestations, and an assessment of the clinical signs evident on the dog the veterinarian can sometimes identify the allergen by two diagnostic tests, an intradermal test for certain allergens or an allergen-specific blood serum test.

Once a definitive diagnosis has been made that it is atopic dermatitis and a specific allergen has been identified, only then can treatment or control of the symptoms be initiated. Many skin disorders such as atopic dermatitis are influenced by the body’s immune system. Most immune mediated diseases including atopic dermatitis are chronic, inflammatory and proliferative. Conventional treatments include corticosteroids and immune suppressant treatments and have been used for decades. These treatments have been effective in improving the symptoms; however, both steroids and immune suppressors have shown complications and side effects with long term application and can be major obstacles to this treatment. There has been some evidence that certain probiotics can help to alleviate these side effects by shortening the length of treatment with immune suppressors, but more work is needed to substantiate that claim. Many therapeutic options for treating atopic dermatitis take aim at control rather than cure, which can make this disease a very frustrating one for both client and veterinarian, not to mention the dog itself. Sublingual immunotherapy, an important breakthrough for allergic veterinary patients, is currently being studied in field trials by veterinary dermatologists and shows considerable promise for future atopic dermatitis therapy.

Food allergies are the third major factor in allergic dermatitis in dogs. To uncover which food or ingredient may be causing the allergic reaction, there needs to be a family commitment to a diet trial to ascertain which food or ingredient is causing the allergic response. To stay on track with these diet trials all dietary information provided by your veterinarian must be followed precisely. Feed your dog only the prescribed diet with no other foods or treats allowed. It is imperative that all family members and friends that may be in contact with the dog must be informed and participate in the feeding trials. Provide no treats, flavored products such as medications or chew toys unless they contain the prescribed ingredients. Do not let your dog eat dropped food either while the family is eating meals in the house or outside from garbage containers, dropped food by passersby or any other source. This trial may take as much as eight weeks of feeding the special diet before clinical improvement is realized. Should the ingredient with which the pet had an allergic reaction is reintroduced into diet, the symptoms will probably reoccur. Only symptoms are alleviated, the underlying allergic reaction remains, many times for the life of the pet.

Veterinarians must determine what is happening to the skin before therapeutic strategies can be employed. It takes a new, healthy skin cell about four to six weeks to mature and be present near the skin surface; therefore, even curable allergic dermatitis cases may take weeks to resolve. For the cases that are not curable, symptomatic signs can be reduced or alleviated altogether; however, should the allergen return, the symptoms will most likely reoccur at some level for the rest of the pet’s life. Because an itchy dog may be suffering from a food allergy, airborne allergy, reaction to insect bites or allergies of unknown causes, it is important that your veterinarian knows all about the lifestyle your dog lives including what he or she eats. Do these symptoms exhibit themselves seasonally when the dog goes outside or when he travels to other locations? To confirm or rule out possible allergic triggers, veterinarians will order tests. The doctor may call for skin scrapings or serum tests to identify airborne allergens as the source of the reaction. Regardless of what caused the problems, tests are required to determine the most effective treatment for your dog. The quicker the diagnosis is made, the less symptoms he will exhibit. Allergic dermatitis cases usually are very frustrating and complicated. It is important that you seek out the services of a veterinarian who has expertise in diagnosing and planning a strategy for controlling these conditions as early as possible after the dog begins to show signs of scratching. And that makes for a happier dog, as well as a happier family.



Bruce W. Little, DVM