Tampa Veterinary | Tampa Newsletter | FL | Cross Creek Animal Medical Centre |

Food allergy is about 10% as common as pollen/mold allergies in dogs and just about as common as pollen/mold allergies in cats. In food allergy, the pet history is that of a non seasonal itching, with little variation in the intensity of itching from one season to another in most cases. Most reports do not suggest a breed predilection; however, one report indicated an increased relative risk in Labrador Retrievers, West Highland White Terriers, and Cocker Spaniels. The age of onset is variable, from 2 months to 14 years old. One report indicated that most food allergies begin at less than 12 months of age.

The distribution of itching and lesions varies markedly between animals.

Ear canal disease manifesting as itching and secondary infection with bacteria (usually Staphylococcus , Pseudomonas , Proteus , or Escherichia coli ) or yeast ( Malassezia pachydermatis ) are common and may be the only presenting complaint.

Other patterns seen include rubbing the eyes, generalized itching, generalized seborrhea, red lesions, or a distribution pattern that may mimic that of pollen/mold allergies (the feet, face, and undersides) or flea allergy dermatitis (the lower back and hindlegs). The most common areas of involvement include the ears, feet, groin, underarm area, front of forelegs, around the eyes, and the muzzle. The degree of itching is usually moderate to severe. Response to anti-inflammatory steroids varies from poor to excellent.

Food allergy remains a confusing allergy to diagnose because there is no 100% reliable diagnostic test other than a strict food elimination diet.

Blood testing and skin testing for food allergens can be unreliable in some cases. The ideal food elimination diet should be balanced and nutritionally complete and not contain any ingredients that have been fed previously to the animal. Many diets contain novel protein or carbohydrate sources (eg, lamb and rice). However, it is often misunderstood that if any previously fed ingredient is present in the elimination diet, the animal may be allergic to that ingredient and the diet trial will be a failure. The key point in any food elimination diet trial is that only novel food ingredients can be fed.

The trial diet should be fed for up to 3 months. If marked or complete resolution of the itching and clinical signs occurs during the elimination diet trial, food allergy can be suspected. To confirm that a food allergy exists and that the clinical improvement was not just coincidental, the animal must be challenged with the previously fed food ingredients and a relapse of clinical signs must occur. The return of clinical signs after challenge is usually between 1 hour and 14 days, although it is usually within 3 days. Once a food allergy is confirmed, the elimination diet should be reinstituted until clinical signs resolve, which usually takes 14 days. At this point, previously fed individual ingredients should be added to the elimination diet for a period of up to 14 days. If itching increases, the individual ingredient is considered positive for having a causative role in the food allergy. If itching does not increase, the individual ingredient is not considered important in causing the clinical signs.

The number of offending food allergens varies from 1 to 5 ingredients per animal. The most frequently identified causative allergens in canine food allergy include beef, chicken, corn, wheat, soy, and milk. Once the offending allergens are identified, control of the food allergy is by strict avoidance of these offending allergens. Concurrent diseases (such as pollen/mold allergy or flea allergy) may complicate the identification of underlying food allergies. Infrequently, the dog will react to new food allergens as it ages.

Clinical presentations of food allergy in cats include small scabs, hair loss, red lesions, and severe head and neck itching. No breed, sex, or age predilection is seen. Age of onset varies from 3 months to 11 years. In one study, 46% of affected cats became symptomatic at 2 years of age, and Siamese cats represented 30% of the cases.

Response to steroids is variable, but about two-thirds of cats show excellent response to steroids initially. Many cats develop a poor response to steroids with repeated treatments. As with canine food allergy, an elimination diet should be fed for up to 3 months. The elimination diet should not contain any previously fed ingredients. Food elimination diets can be difficult in cats because many cats are often reluctant to change diets. Cats should not be starved or forced into eating a new elimination diet due to the serious nature of liver disease that may be induced by prolonged fasting.

Response time to the elimination diets varies from 1 to 9 weeks. Time until relapse of itching after challenge with the offending food varies from 15 minutes to 10 days. The most frequently identified food allergens in cats include fish, beef, and chicken. Avoidance of the offending allergens will control the clinical signs associated with the food allergy.

Special prescription diets from Hills, Royal Canin and Purina are available from veterinarians to test for and to treat food allergies.