Food allergies in the dog and cat (Proceedings)

Food allergy

A. Etiology is a type I hypersensitivity predominantly but a type III and type IV reaction may also occur. Animals are predisposed to develop food allergy through undefined genetic factors.

B. Historical findings

     1. No sex predisposition exists

     2. Breed predisposition may include Labrador retrievers, Shar Pei, English Springer Spaniels, Miniature Schnauzers, Cocker Spaniels, Collies, and Golden retrievers, but any dog may develop food allergy.

     3. Primary complaint is pruritus that is non-seasonal.

     4. Age of onset is usually less than 3 years but may occur later in life or at any age.

     5. Problem persists regardless of the commercial brand of food fed because of the similarity of ingredients. Onset of symptoms is usually not associated with a recent dietary change. Many dogs with food allergies have been on the diet that they are allergic to for 2 or more years before showing clinical signs.

C. Clinical findings

     1. Chief complaint is pruritus

          a. Dog distribution includes the face, feet, forelegs, axilla, ears, and sometimes inguinal or perianal regions (or any combination)

          b. Cat distribution includes the face and neck, especially the pre-aural region between the lateral canthus of the eye and the base of the pinna. Any type of eosinophillic granuloma or miliary dermatitis may also be present.

     2. Urticaria may be present (dogs)

     3. Concurrent GI symptoms are uncommon but can occur.

     4. Seizures are occasionally associated with food allergy

     5. Secondary pyoderma or otitis is common in dogs.

D. Differential diagnoses

     1. Non-seasonal atopy

     2. Scabies

     3. Flea allergy (non seasonal)

     4. Allergic contact dermatitis

     5. Malassezia dermatitis or pruritic pyoderma

E. Diagnosis is only made on the response to a food trial elimination diet

     1. A selected diet (preferably home cooked) that consists of a protein and carbohydrate source that the animal has not eaten for an appreciable length of time is fed. Nothing else passes the lips of our patient other than water. This includes flavored heartworm tablets or vitamins, toothpaste, chew toys, raw hides, etc.

     2. Rabbit, duck, venison, white fish, salmon, kangaroo are possible protein source options. These are usually combined with either potato or rice. Reports exist of cross reactivity between beef and venison exists. Therefore, in severely beef allergic animals this may not be the best protein to chose. Either commercial diets or home-cooked diets are used.

     3. Hydrolyzed diets have recently become available and are considered the Cadillac of the food trial diets. These diets use technology similar to that used in humans. The proteins in these diets are broken down into such a low molecular weight that the body no longer sees them as being foreign. Two of the more popular diets are: Purina HA (hydrolyzed soy) and Hill's ZD ultra. Both diets have different ingredients and molecular weights. Purina HA is hydrolyzed soy with an mw of less than 12,200 Daltons and Hill's ZD ultra is hydrolyzed chicken with less than 3,000 Daltons (no intact proteins). Another variety of Hills ZD is available but does not appear to be as good for food trials (hydrolyzed chicken also less than 3,000 Daltons but it has intact proteins (ie potato). Royal Canin also has a hydrolyzed diet. This diet uses hydrolyzed soy with chicken fat. Two different letters represent the two Royal Canin hydrolyzed products available. HP 19 is the dog formulation whereas the Royal Canin HP 23 is the cat formulation.

     4. The diet is fed for a minimum of 8 weeks or until clinical symptoms of pruritus have decreased significantly. Reports of successful food trials lasting 16 weeks have been documented.

     5. In order for a diagnosis of food allergy to be confirmed, a food rechallenge needs to be performed. These involve feeding the old diet (including treats) to the dog or cat. Clinical symptoms return quickly (hours to less than one week) to confirm the cause and effect. Although not as common, some reports exist that some food allergic animals may take as long as 2 weeks for their clinical signs to recur after rechallenge.

     6. The elimination diet is then given until symptoms subside (usually 1 to 2 weeks). The hypoallergenic diet can be given for life or the dog or cat may be individually rechallenged to determine which food ingredient or ingredients are causing the allergies. A commercial diet can then be selected for long term maintenance based on these rechallenge results. Most animals are allergic to 1 or 2 food ingredients but they can be allergic to as many as 5 different food ingredients.

     7. It is very uncommon that a patient will develop new sensitivities to a selected diet once the diagnosis is made.

     8. Intradermal skin testing with food allergens have been shown to be very inaccurate, and are not recommended.

     9. Serum allergy testing for food allergens is also not recommended due to accuracy problems (many false positives).

F. Treatment involves not feeding the offending allergen

     1. Secondary pyoderma and otitis must be treated

     2. Anti-inflammatory dosages of oral corticosteroids may provide temporary relief of pruritus, but not all respond.

     3. Many new commercial diets have improved the treatment options for food allergic patients. However, many dogs have been exposed to lamb and others and we are running out of novel protein sources for food elimination testing.

Selected readings

Leistra MHG, Markwell PJ, Willemse T. Evaluation of selected-protein-source diets for the management of dogs with adverse reactions to foods. J Am Vet Med Assoc. 219:1411-1414,2001.

Loefller A, Lloyd DH, Bond R, Kim JY Pfeiffer DU. Dietary trials with a commercial chicken hydrolysate diet in 63 pruritic dogs. Vet Rec. 54:519-522, 2004.

Roudenbush P. Hypoallergenic diets for dogs. In: Bonagura JD, ed. Kirk's Current Veterinary Therapy XIII. Small Animal Practice. Philadelphia: WB Saunders; 2000:530-535, 2000.

Tapp T, Griffin C, Rosenkrantz W, Muse R, Boord M. Comparison of a commercial limited-antigen diet versus home-prepared diets in the diagnosis of canine adverse food reaction. Vet Ther. 3:244-251, 2002.