Food Allergy (Canine)

Food allergy is a relatively common immune disease resulting in itchy skin and ears in dogs which can also affect the gastrointestinal tract. Food Allergy is both diagnosed and treated with a novel protein diet (a diet containing a protein that the dog has not encountered before).

Common name: Food allergy
Scientific name: Food allergy, food intolerance, food hypersensitivity, adverse reaction to food

Diagnosis

Signalment
Food allergy can affect dogs from 4 months of age up, but approximately one-third of cases are in dogs under one year of age. It affects males and females equally. Certain breeds appear to be predisposed, including Cocker Spaniels, Labrador Retrievers, German Shepherds and Boxers.

Incidence/prevalence
The exact prevalence of food allergy in dogs is not known; however, 20-30% of dogs with food allergy also have other allergies (i.e., to environmental allergens or fleas).

Geographic distribution
There is no known geographic predilection for food allergy.

Clinical signs (primary, most to least frequent, scientific term, synonyms)
Pruritic skin (itchy skin), otitis (inflamed ears), vomiting and/or diarrhea, flatulence.

Clinical signs (secondary, most to least frequent, scientific term, synonyms)
Pyoderma (skin infection), excoriation (trauma to skin from scratching), lichenification (thickening of skin).

Cause (scientific, common term)
Hypersensitivity reaction (body reacting to the food as if it were a dangerous invader), organ system affected (most to least affected), skin, ears, gastrointestinal tract.

Diagnostic tests
Novel protein diet trial, food challenge, differential diagnosis, environmental allergy, flea allergy, parasite, drug reaction, primary skin infection (caused by bacteria or yeast), primary ear infection (caused by bacteria or yeast).

Ringworm, inflammatory bowel disease, or any gastrointestinal or systemic disease causing vomiting and diarrhea.

Overview

Food allergy is a relatively common immune diseases resulting in itchy skin and ears in dogs which can also affect the gastrointestinal tract. Food allergy occurs when the body's immune system responds to a protein in the food as if it were a dangerous invader. Food allergy is treated with a trial of a “novel protein diet” (a diet containing a protein that the dog has not encountered before), then a re-introduction of the food to which an allergy is suspected. The prognosis for food allergy is very good, as long as the dog's prescribed diet is strictly followed.

Treatment

Home Care
If food allergy is suspected consult a veterinarian, as other causes for the dog's clinical signs must be ruled out. Furthermore, the commercial “novel protein diets” used to diagnose and treat food allergy can only be obtained with a prescription, and home-cooked novel protein diets are best prepared and administered under a veterinarian's direction.

Professional Care
The first step a veterinarian will take in diagnosing a food allergy is to rule out other causes of a dog's clinical signs. The veterinarian will examine the skin for fleas or mites, check the ears for infection, or run tests to rule out other causes of gastrointestinal disease. Food allergy is both definitively diagnosed and treated with a trial of a “novel protein diet:” a diet containing a protein that the dog has not eaten before, such as rabbit or venison (certain prescription foods also exist that contain proteins too small to cause an allergic reaction in most dogs; however, these diets are ineffective in approximately 20% of food-allergic dogs). Novel-protein diets can be home-cooked, but are also available commercially (by prescription). A six- to eight-week novel-protein food trial is followed by a re-introduction of the food to which an allergy is suspected. If the dog's clinical signs resolve on the novel protein diet then recur when the offending diet is re-introduced, a food allergy is presumed to be the diagnosis, and the dog is placed on a novel protein diet for the rest of his or her life.

Action
An owner who suspects food allergy in his or her dog should take the animal to a veterinarian for an examination and diagnostics as needed. Strict adherence to diet recommendations are key. If a dog is on a novel protein diet, ANY other protein (including not only foods, but also flavored heartworm pills or other medications, toothpaste, rawhides or pig's ear chews) will counteract its effects, making it worthless in diagnosing and treating the disease. Your veterinarian may recommend hypoallergenic treats, such as potato chews, or certain fresh vegetables. Always check with your veterinarian before offering anything other than the prescribed diet. A food-allergic dog typically requires 6-8 weeks on a strict novel protein diet before improvement is evident.

Outcome
The prognosis for a dog with food allergy is good with strict adherence to dietary requirements for the animal's life.

Recommended Treatment
See your veterinarian for proper diagnosis and treatment of suspected food allergy.

References/Additional Readings

Duclos D. Food Reactions (Dermatologic). In: Tilley LP and Smith FWK, eds. The 5-Minute Veterinary Consult. Philadelphia: Lippincott Williams & Wilkins, 2004; 488-489.

Hillier, H and Roudebush, P. Food Allergy, Gastrointestinal. In: Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats. St. Louis, Mosby, 2007; 398-400.

Lowe, A. Food Allergy, Dermatologic. In: Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats. St. Louis, Mosby, 2007; 396-398.

Medleau, L and Hnilica KA. Canine Food Hypersensitivity. In: Small Animal Dermatology. Philadelphia: Saunders, 2001; 110-114.

Verlinden A, Hesta M, Millet S and Janssens GPJ. Food allergy in dogs and cats: a review. Crit Rev Food Sci Nutr. 2006; 46(3):259-73..

Author

Andra Gordon-Gatica, DVM

Editor

Steven Hansen, DVM, MS, MBA

DABVT, DABT