Allergy in pets is one of the more common and challenging conditions we see at Manchester Animal Hospital. It is defined as a state of over-reactivity or hypersensitivity of the immune system to a particular substance called an allergen. Most allergens are proteins from plants, insects, animals or foods.
Exposure to the allergen, usually on multiple occasions spanning months to years, sensitizes the immune system, and a subsequent exposure to the same or related allergen causes an over-reaction. Normally the immune system protects the dog against infection and disease, but with allergies, the immune response can actually be harmful to the body. Allergies may be thought of as an unnecessary normal immune response to a benign foreign substance
In the dog, the most common symptom associated with allergies is itching of the skin, either localized (in one area) or generalized (all over the body). In some cases, the symptoms involve the respiratory system, with coughing, sneezing and/or wheezing. Sometimes, there may be runny discharge from the eyes or nose. In other cases, the allergic symptoms affect the digestive system resulting in vomiting and diarrhea. Unfortunately, allergies are quite common in dogs of all breeds and backgrounds. Most allergies appear after the pet is six months of age, with the majority of affected dogs over age one or two.
A very large number of substances can act as allergens. Most are proteins of insect, plant or animal origin, but small chemical molecules 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. Insect bite allergy is the exaggerated inflammatory response to the bite or sting of an insect. Arachnids such as spiders and ticks, and insects including fleas, blackflies, deerflies, horseflies, mosquitoes, ants, bees, hornets and wasps, can cause an allergic reaction in sensitive dogs. Flea saliva is by far the most common insect allergen in dogs, causing flea allergy dermatitis (FAD). While most dogs experience minor local irritation from flea bites, the FAD dog will react to a single bite with severe local itching.
Food allergy or food hypersensitivity can develop to almost any protein or carbohydrate component of food. It most commonly develops in response to protein of the food; dairy products, beef, wheat gluten, chicken, chicken eggs, lamb and soy are commonly associated with food allergies in dogs. 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 typically does not respond well to corticosteroids or other medical treatments.
Contact allergy is the least common type of allergy in dogs. It results from direct contact to allergens, such as pyrethrins found in flea collars, pesticides used on the lawn, grasses, materials such as wool or synthetics used in carpets or bedding, etc. Contact allergies can develop to practically anything and at any age. If the dog is allergic to any of these substances, there will be skin irritation and itching at the points of contact, usually the feet and stomach. Removal of the allergen (once it can be identified) often solves the problem.
The term inhalant allergy in the dog is often called atopy. The main inhalant allergens are tree pollens, grass pollens, weed pollens, molds, mildew, and house dust mites. Many of these allergies occur seasonally, however, others such as molds, mildew, and house dust mites occur year-round. When humans inhale these allergens, the resulting allergy primarily manifests with upper respiratory signs: runny eyes, runny nose and sneezing.
Symptoms of atopy can be controlled but a permanent cure is not usually possible. Most dogs that have inhalant allergy start showing signs between one and three years of age. Affected dogs will often react to several allergens and often experience concurrent flea or food allergies. If the offending allergens can be identified by intradermal skin tests (skin testing) or blood tests, the dog should be protected from exposure to them as much as possible. Because most of these allergens are environmental, this is difficult and recurrent bouts are likely. Symptoms of atopy can be controlled but a permanent cure is not usually possible. Treatment depends largely on the length of the specific allergy season. It may involve one or more of the following three therapies:
Anti-inflammatory therapy: Treatment with anti-inflammatory drugs such as corticosteroids, or with 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. Recently-approved drugs such as oral cyclosporine are also very beneficial in treated atopy and have fewer long-term side effects than corticosteroids.
Shampoo therapy: Frequent bathing with a hypoallergenic shampoo can be soothing to itchy, inflamed skin. Bathing also rinses out allergens in and on the coat that can be absorbed through the skin. Some therapeutic shampoos also contain anti-inflammatory ingredients that may further benefit your pet.
Hyposensitization or desensitization therapy: If the specific offending antigens are identified by allergy testing, an allergy injection serum or allergy shots can be given to the patient. With this treatment, very small amounts of the antigen are injected weekly. This repeated dosing has the objective of reprogramming or desensitizing the immune system. Success rates vary with this treatment. Approximately 50 percent of treated dogs will see significant improvement in their clinical signs, while approximately 25 percent more will see a decrease in the amount or frequency or corticosteroid usage
Treatment requires identifying the offending component(s) of the diet and eliminating them. The most accurate way of testing for food allergies is with an elimination diet trial using a hypoallergenic diet. Because it takes at least eight weeks for all other food products to be eliminated from the body, the dog must eat the special diet exclusively for eight to twelve weeks. If the diet is not fed exclusively, it will not be a valid test. All table food, treats, and flavored vitamins must be discontinued during the testing period. There may be problems with certain types of chewable tablets or medications such as heartworm preventive. Your veterinarian will discuss the specific diet and restrictions recommended for your dog.
The symptoms of allergies can be confused with other disorders or occur concurrently with them. Therefore, do not attempt to diagnose your dog without veterinary professional assistance. Be prepared for your pet to receive a full diagnostic evaluation to rule out other causes of itching and skin problems.
Dr. Lamb is the Veterinarian at the Manchester Animal Hospital.
