What are allergies?
The role of the immune system is to keep infectious microorganisms, such as certain bacteria, viruses, and fungi, out of the body, and to destroy any infectious microorganisms that do invade the body. Allergies are the result of inappropriate response to a substance which would usually be considered harmless (such as a type of food, pollen etc). In an allergic animal, the immune system over reacts to the substance and mounts an immune response against it.
Food Allergies in cats
Food allergies are the third most common type of allergy in cats (behind flea allergy and inhalant allergy). This is caused by an allergic reaction to one or more ingredients in the cat's food. The most common causes of food allergies are fish, beef, chicken, eggs and wheat. Cats become allergic to foods they have eaten for a long period of time (usually two years or more). There is no breed, sex or age predilection. Cats with other allergies (such as inhalant) may be at greater risk of developing food allergies. There appears to be a genetic component.
What are the symptoms of food allergies in cats?
Symptoms of food allergies occur over a period of months. The most common signs of food allergy include:
Nonseasonal itching, especially on the front half of the body, head, face, ears, and neck.
Otitis externa - Itching and scratching can lead to inflammation and sometimes infection of the ears.
Excessive licking of the affected skin.
Affected areas of the skin may develop papules (small, fluid-filled bumps).
Hair loss (due to excessive scratching, grooming etc).
Diagnosis of food allergies in cats:
There is no blood test to diagnose food allergies. Your veterinarian will need to rule out other common disorders which have similar symptoms (such as flea allergy dermatitis, inhalant allergy, ringworm, mange). Once this has been done, he will place your cat on a food elimination trial. This usually lasts between 8-12 weeks. During this time, you must not give your cat any other foods, vitamins, minerals or chewable medications apart from the prescribed diet. If any other foods or vitamins are given during this trial it will invalidate the results. If the allergy clears up after the specified time then a food allergy is the likely cause. The diet given to your cat during the trial will be a food the cat has never had before such as rabbit, duck or venison. The diet may be home made or a special 'prescription' diet.
Recent advances have lead to the creation of hypoallergenic diets containing "hydrolyzed protein" which involves breaking down the protein into individual amino acids which are too small for the immune system to detect (and react to). Two commercial brands are Hills z/d and Royal Canin Hypoallergenic. Food elimination diets must contain only one protein and one carbohydrate.
After the food trial, you may be asked to 'challenge' your cat by re-introducing your cat to his usual diet to see if the allergy returns.
If there is no reduction in your cat's symptoms after 2-3 months on the food trial, food allergy may not be the problem and other causes will need to be investigated. The most common of which inhalant allergy.
Treatment of food allergies:
Avoiding the food which caused the allergies is the best method of treatment. This may either be a homemade diet using novel ingredients (such as kangaroo) or the use of commercial hypoallergenic one. If you are feeding a home made diet it is important to ensure that your cat is receiving the correct nutrients in the diet.
Corticosteroids may be prescribed to control itching. Unfortunately, not all cats will respond to this treatment.
Antihistamines to control the itching.
Antibiotics may be required to treat skin infections caused by itching.
If you have decided to feed your cat a homemade diet, you may choose at times to introduce a new meat and see how your cat reacts to it. For example, you have your cat on a diet of kangaroo meat and the allergies go away, introduce beef and see how he reacts. If there are no signs of allergies over a few weeks you know you can feed him this, introduce lamb, watch for signs of allergies returning etc. This way, you can slowly increase the type of food your cat can eat.
Occasionally new food allergies develop over time, if this happens then it will be necessary to re-evaluate the new diet.