Allergic Skin Diseases
by Marion Coffman
This article is by Marion Coffman. For those of you who enjoyed the previous article by Marion Coffman - we have a feast ahead. She has been kind enough to send us a range of articles on various issues that will appear in future newsletters - thanks Marion.]
Most breeds of dogs have allergies to certain substances, the 3 most common being food, inhaled substances, or injections such as vaccines, insect bites or drugs.
The most devastating allergic reactions come from injected allergens, most often insect bites. By the time the owner realises that his dog has been bit and is suffering distress, it is often too late to save the animal. The reaction to a bite can be so immediate that there isn't enough response time available and the dog will go into shock and respiratory failure.
Inhalant allergies and food allergies represent the most common reactions, not related to parasites, in dogs. Most of these allergy problems are not life threatening but interfere with the full enjoyment of life because of the annoyance of skin, gastrointestinal, and respiratory problems. Besides being a source of discomfort to the dog, they are also frustrating to the owner looking for a solution to the problem.
Allergic inhalant dermatitis is one of the most common skin problems presented to the veterinarians. Affected dogs react to a variety of inhalants including house dust, feathers, grass, tree and weed pollen. Moulds often cause allergies and occur all year long. They produce a vast number of small spores that outnumber even the pollen in the air. This is especially hard on owners of hunting dogs as the allergy causes immediate reaction of wheezing, coughing, chewing at the feet and discharge in the eyes.
More often though, inhalant allergies will show up as they affect the skin. Dogs develop itchiness, hair loss and hives in the groin, flanks and armpits. Many dogs rub their faces on the furniture to relieve the itching and inflammation on the face and ears. Secondary skin infections develop in the traumatised areas, resulting in hot-spots - red and moist lesions with hair loss in the center. Antibiotics are needed to combat the infections and testing can be done to determine which allergies affect your dog.
Veterinary dermatologists usually rely on skin tests to confirm the diagnosis and to identify specific allergens to which the dog is allergic. Skin testing involves shaving the hair off the dogs side, then injecting minute amounts of allergy extracts of various compounds known to cause allergy. The skin is examined at 15 minutes and again at 30 minutes. Swelling and inflammation around one or more of the test substances helps identify the culprit and, once the cause is known, hypo-sensitisation can be attempted. Although individual responses vary, most dogs can be sufficiently desensitised to give them relief.
Having your dog avoid inhalant allergens is rarely practical unless it is proven that the problem is a contact allergy. In that case environmental control can be aimed at by limiting the exposure to the allergens by removing substances such as wool, house plants and even plastic food dishes. Topical therapy using a variety of shampoos will often make the allergic dog more comfortable. Colloidal oatmeal can also be added to the bath water and has a soothing effect.
Immunotherapy (allergy shots) is a slow process sometimes taking up to a year before improvement. Antihistamines are useful and the advantage in using them is that they are relatively safe compared to corticosteroids.
Some dogs develop allergies to food, rawhide chews, medications or other ingested substances. These allergies most often show up as skin problems and not as digestive upsets. Although food allergies are relatively uncommon they are an important cause of severe itching in dogs. The clinical signs of food allergy are very much like those of many other allergic conditions except that clues that the diet is at fault may be that food allergy is not seasonal and that, unlike flea or inhalant allergy, it is not easily relieved by treatment with corticosteroids. Since food allergy is uncommon, other sources should be excluded before you blame it on the diet.
Many affected animals have been fed the offending food 2 or more years before developing any clinical signs. Clinical signs may develop at any age, even appearing before the dog is 9 months of age or after the dog is old (more than 8 years).
For most food hypersensitivities the symptoms are all year round, being typically abrupt in onset and only affecting one dog in the household though all are on the same diet. The symptoms may progress to loss of appetite, weight loss, itchy reddened skin and hair loss especially on the head, feet, armpits, groin and ears. Vomiting, diarrhea, sneezing, asthma-like conditions and behavioral changes may occur.
The only way to be certain that the diet is the problem is by dietary restrictions. Just changing from one commercial pet food to another is not the answer because many of these diets contain the same ingredients. The most common causes of food allergies are beef, pork, chicken, milk, corn, soy, whey, eggs, fish and preservatives.
The easiest way to check for food allergies is to put the dog on an elimination diet. This diet usually consists of nothing except pure lamb (editors note: remember that all sheep products in New Zealand should be cooked or frozen to standards required for destruction of hydatids and sheep measles) and rice. Your veterinarian will work out with you to reintroduce particular foods until the offending ingredients are discovered.
Hypoallergenic diets must contain ingredients not previously encountered by the patient and all other sources of potential or offending substances should be excluded including rawhide chews, table scraps and vitamin and mineral supplements.
Response to the hypoallergenic diet rarely occurs within the first week. If the dogs skin condition improves by the twenty-first day diet is probably at fault and the animal will be put back on the original diet. If the animals itchiness increases, there is no doubt what the problem is. In this case you will need to find a diet that is both nutritionally sound and free of the offending substances.
Many food allergic dogs can safely eat commercially prepared hypoallergenic diets. Introduction of individual dietary antigens can be based on a list of ingredients in the dogs original commercial meal. For the dog eating foods containing dried whey, powdered milk can be mixed into the daily ration. If there is no resumption of the itching within 7 days, ground beef can be substituted for the lamb. If neither of those ingredients causes itching, wheat flour and then soy or corn meal can be added in a similar manner. If there still is no resumption of itching, the dog can be placed on a commercial diet free of additives, preservatives and artificial flavours and colours.
Avoidance of the offending foods is the only specific and practical treatment of food allergies.