Food allergy with cats
General information
Other common/scientific names: food hypersensitivity, adverse reaction to food, food intolerance
A food allergy is a disorder in which eating a particular food or food additive causes an allergic reaction in the cat. Usually the symptoms are limited to the skin or the gastrointestinal (g.i.) tract, although sometimes both systems may be affected. Food allergies may develop at any time during a cat’s life, so cats that have tolerated the same food for years may one day have an allergic reaction to that food. About 10-15% of all allergic skin disease is caused by a food allergy. Siamese cats appear to have an increased risk of developing a food allergy.
Causes
Although a variety of ideas have been proposed, the exact causes of food allergies are not completely understood. It is thought that the majority of food allergies are due to an abnormal response of the immune system. Cats with an abnormal mucosal barrier of their g.i. tracts also seem to be at greater risk of developing a food allergy.
Common food allergens that cause skin disease in cats are beef, dairy products, and fish, although any food or food additive can be the trigger for a food allergy.
Cardinal symptom
•Intense itchiness, often around the head
•Vomiting
•Diarrhea
•Weight loss
Symptoms
The most common sign seen in the skin of a cat with a food allergy is intense itchiness around the cat’s head, neck and ears. Often hair loss, scratches, sores and scabs caused by self-trauma are seen in these areas as well, and the skin may be secondarily infected. Sometimes the itchiness is generalized and small raised lesions and crusts may be seen over much of the cat’s body. In some cases, eosinophilic placques and linear granulomas are seen as well. Often ear infections and eye infections are also present. Note that the observed signs do not vary with the seasons, as they often do in atopy, which can cause similar skin problems.
Cats with g.i. signs due to a food allergy often have a history of vomiting, soft stools or diarrhea, and weight loss. Flatulence and an increased frequency of defecation are also frequently noticed. Often the cat’s appetite is decreased and there are intermittent signs of abdominal pain and distension.
Diagnosis
To make a diagnosis of food allergy the veterinarian will first want to eliminate other common diseases that could cause similar clinical signs. Fleas, mites, and ringworm will need to be excluded as the underlying cause if the cat is itchy and has skin lesions. Bloodwork, x-rays, and ultrasound may be recommended to eliminate other common causes of g.i. disease. Evidence which may support a diagnosis of food allergy is nonseasonal itchiness and a poor response to corticosteroid therapy.
Once other common diseases have been excluded, a definitive diagnosis of food allergy can be made performing an elimination food trial for 8-12 weeks. Although time-consuming and sometimes difficult, this is the only useful test to truly confirm a diagnosis of food allergy. Both intradermal skin tests and blood tests for food allergens are unreliable.
The diet used for the elimination food trial should be nutritionally balanced and consist of a single “novel” protein and a single carbohydrate. A “novel” protein is one that the cat has never previously eaten, perhaps venison or pork. Commercial diets are available that can be used, or a home-cooked diet may be prepared. Once the diet has been properly introduced and accepted by the cat, this diet and only this diet can be fed to the cat for the duration of the 8-12 weeks. No other food (including treats, vitamins, chewable medicines, or table scraps) can be fed while the food trial is being performed. This may mean that an outdoor cat will need to be kept indoors during the food trial, or that the whole cat household will need to be eating the same food for the duration of the trial!
If a food allergy is present, cats with itchiness will generally improve within 4-6 weeks on the new diet, although in some cases it may take up to 12 weeks. Cats with g.i. symptoms due to a food allergy typically improve within 4-8 weeks.
If improvement has been seen at the end of the 8-12 weeks on the new diet, there is still one step left to confirm a diagnosis of food allergy. At the end of the 8-12 weeks, the original diet is then fed back to the cat for 10-14 days. If the signs return, a diagnosis of food allergy can be made. If the signs do not return, it is unlikely that any improvement was the result of the new diet, and food allergy cannot be diagnosed. In some cases a second food elimination trial using a different diet is necessary to reach a diagnosis.
Treatment
Individual ingredients can be added to the elimination diet one by one to see if signs recur. In this way the specific ingredient or ingredients that caused the allergy may be determined and avoided. A commercial diet that does not include the offending ingredients should then be fed. Because there is a greater risk of nutritional problems developing with the extended use of home-cooked diets, these kinds of diets are not typically recommended long-term.
Prognosis
If the offending food or food additive can be avoided, the prognosis is excellent.
Prevention
Cats with one sort of allergy often have other types of allergies. About 20-30% of cats with a food allergy also have atopy or a flea allergy. It appears that a cat may not show any symptoms until the collective total of its exposure to allergens reaches some critical threshold level. Once this level is exceeded, it will begin to have symptoms. For this reason, preventive measures should be taken to ensure that any cat with a food allergy is kept free of internal and external parasites which could contribute to its overall allergen level.
Tips
When introducing a new diet to a cat, go slowly! Cats can be finicky, and if a cat stops eating it can quickly develop hepatic lipidosis, which can be life-threatening. Introduce a new food by mixing a small amount of it with your cat’s regular food. You may want to start off with as little as one part new food to nine parts old food. Once your cat is eating this mixture well, gradually increase the percentage of the new food every 5-7 days until the cat is eating 100% of the new food. This may take several weeks and may delay the start of your food elimination trial, but in the end it will be worth it!