Allergies, Canine

What is an allergy?
An allergy is a state of over-reactivity or hypersensitivity of the immune system to a particular substance called an allergen. Most allergens are proteins. The allergen protein may be of insect, plant or animal origin. Repeated exposures  to the allergen may over-sensitize the immune system, such that a subsequent exposure to the same or related allergen causes an over-reaction. This means that the immune response, which normally protects the dog against infection and disease, can actually be harmful to the body.

What are the symptoms of allergies in dogs?
The most common symptom associated with allergies is itching of the skin, either localized (in one area) or generalized (all over the body). Another group of symptoms involves the respiratory system with coughing, sneezing, and/or wheezing. Sometimes, there may be runny discharge from eyes or nose. The third manifestation, which occurs in some cases of food allergies, involves the digestive system resulting in vomiting and diarrhea.

What are the common allergy-causing substances (allergens)?
A very large number of substances can act as allergens. Most are proteins of insect, plant or animal origin, but small chemical molecules known as haptens can also cause allergy. Examples of common allergens are pollens, mold spores, dust mites, shed skin cells (similar to “pet allergies” in humans), insect proteins such as flea saliva, and some medications

What is Flea or Insect Bite Allergy and how is it treated?
Flea allergy is the exaggerated inflammatory response to a flea bite or other biting insect. Flea saliva is the most common allergen. It is a common allergy of dogs, although only a minority of dogs becomes allergic. Most dogs experience only minor irritation from flea bites. However, in a dog that is allergic to flea or insect bites may react to a single bite with severe local itching. It will bite and scratch itself and may remove large amounts of hair, especially in the tail-base region. Secondary bacterial infection may occur in the broken skin. The area most commonly involved is over the rump in the tail-base region and the hind limbs.

Because one flea can be a problem for the allergic dog, strict flea control is essential, and with modern medications you should be able to provide a flea-bite free environment for your dog (see Fleas for additional information). When strict flea control is not possible or in cases of severe itching, anti-histamines or corticosteroids (also referred to simply as "cortisone" or as "steroids") can be used, under careful veterinary guidance, to block the allergic reaction and give relief. If secondary bacterial infection is present, appropriate antibiotics will be prescribed.

What is Atopy and how is it treated?
The term "Atopy" or "Atopic Dermatitis" refers to allergic itching in the skin as a direct result of skin contact with environmental allergens. The main causative allergens are tree pollens (cedar, ash, oak, etc.), grass pollens, weed pollens (ragweed, goldenrods, etc.), molds, mildew, and house dust mites. Many of these allergies occur seasonally, such as such ast hose caused by grass, tree, and weed pollens. However, others such as molds, mildew, and house dust mites are year-round. When humans inhale these allergens, the allergy manifests mainly with respiratory signs – runny eyes, runny nose, and sneezing (“hay fever”). But in dogs the result is itchy skin.

Most dogs that have atopy start showing signs between one and three years of age. Affected dogs will often react to several allergens. In most cases  the offending allergens can be identified by blood tests and once those have been determined,  the dog should be protected from exposure to them as much as possible. But this is difficult and recurrent bouts are likely. These allergies can be treated but a permanent cure is not usually possible.

Treatment depends largely on the length of the dog's allergy season. It involves three approaches: 

Anti-inflammatory. Treatment with anti-inflammatory drugs such as corticosteroids or antihistamines will quickly block the allergic reaction in most cases. Fatty acid supplementation of the diet can improve the response to steroids and antihistamines in some cases. Newer drugs such as oral cyclosporine may hold promise for severely atopic dogs.

Shampoo therapy. Frequent bathing with a hypoallergenic shampoo can be soothing and helpful. The bathing may also rinse out allergens in the coat that could be absorbed through the skin. Some therapeutic shampoos contain anti-inflammatory ingredients that may further benefit your pet. 

Hyposensitization therapy. The third major form of allergy treatment is hyposensitization with specific antigen injections or "allergy shots". Once the specific sources of allergy are identified by allergy testing, very small amounts of the antigen are injected weekly. This repeated dosing has the objective of reprogramming or desensitizing the immune system. Results are sometimes good but success is variable. Approximately fifty-percent of treated dogs will see significant improvement in their clinical signs while approximately twenty-five percent more will see a decrease in the amount or frequency or corticosteroid usage.

What is Food Allergy and how is it treated?
Food allergy can develop to almost any protein component of food. It most commonly develops in response to the protein of the food of a particular food origin; beef, pork, chicken, or turkey are commonly associated with food allergies. Food allergy can develop at almost any age.

Food allergy may produce any of the clinical signs previously discussed including itching, digestive disorders, and respiratory distress. Food allergy may occur with other allergies, such as Atopy.

Food allergy does not respond well to corticosteroids or other medical treatments. Treatment requires identifying the offending component(s) of the diet and eliminating them. Testing for specific food allergies by blood tests is unreliable, so a hypoallergenic diet trial is necessary. Because it takes at least eight weeks for all other food products to be removed from the body, the dog must eat the special diet exclusively for eight to twelve weeks. If a positive response and improvement of your pet’s clinical signs occurs, your veterinarian will advise you on how to proceed. It must be emphasized that if the diet is not fed exclusively, it will not be a valid test. All table food, treats or vitamins must be discontinued during the testing period. There may be problems with certain types of chewable tablets such as heartworm preventative. Your veterinarian will discuss this with you.

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