Common Allergies in Cats
An allergy is an unpleasant physical reaction caused by the cat's immune system overreacting to a food, something inhaled, or something in the cat's environment. Without an immune system, any animal would not be able to build up resistance to viruses, bacteria, foreign proteins, and other irritating substances that get into the system. Sometimes, however, the immune system reacts to things that aren't really a danger. Certain foods or substances such as pollens, powders, feathers, wool, house dust, and insect bites trigger a reaction typified by itching and sometimes sneezing, coughing, swelling of the eyelids, tearing, or vomiting and diarrhea. This reaction occurs in cats as well as in humans. In rare instances, the immune system reacts against the cells of the cat's own body-these are autoimmune problems.
For a cat to be allergic to something, exposure must occur at least twice. What the cat is allergic to is called the allergen. The way the body responds to that allergen is called a hypersensitivity reaction or an allergic reaction.
There are two kinds of hypersensitivity reactions. The immediate type occurs shortly after exposure and produces hives and itching. Hives in the cat are characterized by sudden swelling on the head, usually around the eyes and mouth, and occasionally the appearance of welts elsewhere on the body. The delayed reaction produces itching that occurs hours or days afterward. Flea bite dermatitis is an example of both types. This explains why a cat may continue to itch even after fleas have been removed from the cat and the environment.
Cats may become allergic to certain foods or substances in foods. The most common food allergens are chicken, fish, corn, wheat, and soy; cats may also develop a food allergy to beef, pork, dairy products, or eggs. An intensely itchy rash often develops on the head, neck, and back, and may be accompanied by swollen eyelids. You may see hair loss and oozing sores from constant scratching. Sometimes, only the ears will be involved. In those cases, the ears will be very red and inflamed and may have a moist discharge. Less frequently, food allergy produces diarrhea or vomiting.
Treatment: Diagnosis is made by feeding the cat a diet without the suspected food for at least four to six weeks. The next step is exposing the cat to a suspected allergen and then watching to see if a reaction follows. There are numerous hypoallergenic diets available.
Atopic Dermatitis (Inhalant Allergy)
This is an allergic skin reaction caused by breathing pollens, house dust, molds, and other allergens indoors or outdoors. It may or may not occur seasonally. Signs and symptoms vary. They include itching on the head and neck, a rash along the neck and back similar to that described for feline miliary dermatitis, skin eruptions similar to those described in eosinophilic granuloma complex, and symmetrical hair loss over the body caused by excessive licking and grooming.
Atopic dermatitis is difficult to distinguish from other allergic skin disorders, such as those caused by insect bites, food hypersensitivity, and chemical contact. Diagnosis is best made by intradermal skin testing.
Treatment: Best results are obtained when the allergen can be identified and eliminated from the cat's environment. However, that is often not possible. Pollens, molds, and dusts can blow in through open windows and affect even indoor cats. Antihistamines or corticosteroids are beneficial in relieving symptoms but do not cure the problem. Allergy shots to hyposensitize the cat have been effective in some cases. Omega-3 fatty acids may also contribute to the cat's comfort and relieve some symptoms.
Immune-Related Skin Problems
The pemphigus complex represents the most common autoimmune skin conditions in cats. This is a group of skin diseases involving inappropriate immunological attack against one of the normal layers of the skin. Different types of pemphigus involve different areas of the skin.
Pemphigus foliaceus is the most common form seen in cats. The feet and the head are affected first, with the appearance of pustules that progress to crusts. The nose often loses its pigment. The cat may itch and, if the feet are involved, she may be lame. Cats with a severe case may have a fever, lethargy, and loss of appetite. A biopsy is the ideal way to make a diagnosis. Treatment involves the use of corticosteroids, immunosuppressive drugs, and, in some cases, gold injections.
Pemphigus erythematosus is a milder form and may be related to sun exposure. Signs are usually limited to the face and ears. Topical steroids may control this condition.
This article is excerpted from “Cat Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
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