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Veterinarian Technician June 2008 (Vol 29, No 6)

Diagnosis and Management of Food Allergies in Dogs and Cats

by Vera M. Steinbergen, CVT, Amanda Gordon, BS, CVA

    CETEST This course is approved for 0.5 CE credits

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    Dogs and cats with adverse reactions to food show an abnormal response to an ingested food or food additive.1,2 These adverse reactions are classified into two categories: (1) food allergy or hypersensitivity and (2) food intolerance.3 Food allergy or hypersensitivity is an adverse reaction to food caused by an immunologic response (typically IgE-mediated type I hypersen­sitivity; however, types III and IV also are highly suspected),4 whereas food intolerance is an adverse reaction to food due to a nonimmunologic cause (e.g., food poisoning, garbage ingestion, ingestion of chocolate or onions).1-4

    Although pets routinely ingest a number of diverse foods, food-related reactions occur relatively infrequently.1 Adverse food reactions are thought to account for only 1% to 6% of all canine and feline dermatoses in general practice and 10% to 20% of all cases seen in dermatology practices.1,5-12 Although some adverse reactions can occur within minutes of exposure to the allergen, delayed responses can take several hours — or even days — to develop.1,3

    Signalment

    Dogs

    No sex or age predilections have been re­ported for dogs with food allergies6; however, several researchers indicate that 33% of the dogs that were studied were less than 1 year of age when they developed clinical signs of food allergies.13 Most researchers have not identified a breed disposition.6 However, other researchers have found that certain canine breeds — soft-coated wheaton terriers, Dalmatians, West Highland white terriers, collies, shar-peis, Lhasa apsos, cocker spaniels, springer spaniels, miniature schnauzers, Labrador retrievers, dachshunds, poodles, German shepherds, golden retrievers, and boxers — are more prone to developing food allergies.12-15

    Cats

    No sex predilection has been reported in cats with food allergies.6 In addition, no age predilection has been documented; however, the mean age of onset of clinical signs in cats is 4 to 5 years.6 Two studies reported that two-thirds of cats with food allergies were Siamese or Siamese mixed breeds, suggesting that this breed might be at increased risk.10,13

    Clinical Signs

    In dogs, nonseasonal pruritus (i.e., itching), sometimes accompanied by gastrointestinal (GI) problems, is the most common clinical sign of food allergies.10 Pruritus is usually generalized but may occur on the feet, ears,16 face (muzzle and chin),2 and inguinal region.13 Perianal pruritus also can be an indication of food allergies.17 In dogs with adverse reactions to food, several primary and secondary skin lesions can develop. These lesions may include papules, erythroderma, excoriations, hyperpigmentation, epidermal collarettes, pododermatitis, seborrhea sicca, and otitis externa.1,18 Dogs with adverse reactions to food may develop recurrent skin infections, often related to Staphylococcus intermedius or Malassezia spp.17 In 10% to 15% of dogs with skin infections caused by adverse reactions to food, concurrent GI signs (e.g., vomiting, diarrhea, frequent defecation, colitis)4 developed.3,10,19 Neuro­logic signs, such as malaise and seizures, have been reported.3,16,18 Although asthma and other respiratory signs have also been reported, these clinical signs are rare.3,16,18

    Nonseasonal pruritus is the most common, consistent clinical finding in cats with food allergies.6 Affected cats often present with generalized pruritus; pruritus of the head, face, pinnae, or neck; miliary dermatitis; symmetric alopecia; or eosinophilic granuloma complex lesions.6,18,20-22 In one study, one-third of the cats with adverse food reactions developed angioedema, urticaria, or conjunctivitis.1,22 GI signs (usually diarrhea, but sometimes vomiting) occur in 10% to 15% of feline patients with food allergies.6,7,23 In one study, 33% of pruritic cats with food allergies also had concurrent GI problems.24

    Diagnosis

    For patients with suspected food allergies, a thorough patient history, including a detailed dietary history,a should be obtained and a complete physical examination should be performed. Before the clinician can make a tentative diagnosis of food allergy, other pruritic disorders, such as atopy and flea allergy dermatitis,1 must be ruled out.4 Therefore, it may be necessary to obtain skin scrapings, cytology samples, or fungal cultures, depending on physical examination findings as well as the patient's clinical signs and history.4

    It is often difficult for clinicians to diagnose food allergies in dogs and cats for several reasons:

    • Presence of clinical signs of other allergies or conditions2
    • Presence of secondary infections2
    • Inaccuracy of history provided by the client2
    • Lack of diagnostic tests available25

    Several tests, including intradermal skin testing and serum chemistry allergy testing (e.g., ELISA, radioallergosorbent test), have been described for diagnosing food allergies; however, these tests are generally believed to be inaccurate for this purpose.4,26

    New diagnostic methods, however, are always being developed. In human patients with suspected GI-related food allergies, the use of the colonoscopic allergen provocation (COLAP) test is being studied. During the COLAP test, the duodenal mucosa is challenged with potential allergen extracts via endoscopy or other noninvasive means. The presence of a mucosal wheal and flare is evaluated to determine the possibility of a reaction. The COLAP test, however, is considered controversial in human medicine because not all researchers agree that GI-related food allergies exist.27 The COLAP test has only recently been studied in veterinary medicine.25,28 More research is still needed to determine the role of the COLAP test as a viable diagnostic tool for veterinary patients.

    Currently, the ideal method of diagnosing food allergies in dogs and cats is to initiate dietary elimination and challenge studies.1,10,13,21,22 These trials are time consuming; however, they are the most effective way of identifying a particular allergen.

    Food Elimination Trials

    The goal of a food elimination trial is to feed an affected dog or cat a novel protein diet to which it has not been previously exposed in order to try to eliminate the offending allergen from the pet's diet. The ideal elimination food must meet the following criteria1:

    • Contain only one or two novel protein sources
    • Have high-protein digestibility (>87%) or contain a protein hydrolysate
    • Be free of food additives
    • Contain no excessive levels of vasoactive amines (e.g., histamine)
    • Be nutritionally adequate for the pet's species, age, and lifestyle

    Since there is no "standard" diet — commercial or homemade — for every pet, the clinician must select a diet after carefully investigating all of the foods to which a pet has already been exposed.6,7 For testing purposes, the owner can opt to feed the pet a homemade diet or a commercially prepared diet.1

    Although the American Academy of Vet­erinary Dermatology surveyed veterinarians and reported that homemade foods were recommended more frequently,29 homemade diets are labor intensive for the owner and may not provide adequate nutrition for the pet, especially young, growing animals.29,30 If the owner decides to feed the pet a homemade diet, a veterinary nutritionist should be consulted to make sure that the diet is nutritionally adequate. Numerous factors must be taken into consideration when making a homemade diet. For example, cats should have taurine (unflavored) added to their diet.4 Also, it is important to keep in mind that it can be difficult for owners to consistently make enough food for large-breed dogs and to make diets palatable for cats.4

    Another option is for the owner to feed the pet a hypoallergenic commercial diet. There are numerous commercial pet foods available with limited and different protein sources.1 Commercial pet foods offer numerous benefits. These diets (1) are convenient, (2) often contain novel protein sources, and (3) are nutritionally balanced and complete for the intended species.1 It is important to note, however, that not all commercial foods have been adequately tested in dogs and cats with known food allergies, especially those with dermatologic or GI signs.1,13,19,31-34

    Client compliance is crucial to the success of an elimination trial. The owner should be instructed to give the pet only water and the elimination diet — no other foods or flavored substances. The elimination diet should be fed to the pet for 8 to 12 weeks.18 During this time, treats, flavored vitamin supplements, flavored chewable medications, fatty acid supplements, and chew toys should be avoided.1 Flavored medications should be replaced by equally effective nonflavored preparations.16 Malt-flavored toothpastes should be used instead of protein-flavored toothpastes.16 The owner should be instructed to keep a daily dietary log and to record observations regarding the pet's clinical signs.1 When owners are encouraged to provide detailed daily accounts and bring that information with them during recheck examinations, clinicians are more likely to get a better idea of how the pet is really progressing. If the animal's clinical signs do not improve while the pet is on the diet, another trial using a different commercial diet or a homemade diet should be considered. After the dog or cat has been on the diet for an adequate amount of time and has shown some response, the pet's diet should be challenged.35

    Challenge Diet

    After a pet responds to the elimination diet, the animal should be challenged with its previous diet to confirm the diagnosis of food allergies.35 Clinical signs usually appear within 2 weeks of initiating the pet's regular diet.35 At this point, the pet should be fed the elimination diet again and then challenged with the suspected allergens individually.35 Each specific allergen should be added to the pet's diet one at a time for 1 to 2 weeks to determine which of the allergens is causing the adverse food reactions (see common allergies ).35 After the offending allergen has been identified, the veterinary staff can help the owner select an appropriate diet. For pets with adverse food reactions, the most effective treatment is to just avoid feeding the pet a diet that contains the offending food allergen.1

    Role of the Technician

    As mentioned previously, client compliance is extremely important when a food allergy is suspected in a pet. Veterinary technicians are often the main source of information when the client has questions regarding the clinician's recommended dietary changes. Tech­nicians can help clients by following up with them on a regular basis to make sure that they are feeding the pet the elimination diet and no other forbidden foods. In addition, technicians can communicate to pet owners the importance of keeping a food diary during a food elimination trial. Technicians can show owners how to properly fill out the diaryb and then follow up with them during the trial to answer any questions that they may have. They can also question the owner during follow-up to make sure that he or she is tracking the progression of the pet's clinical signs. Once the offending allergen has been identified, the technician can work with the owner to find an appropriate diet that is palatable to the pet.

    Conclusion

    It can be very frustrating for owners when pets develop clinical signs related to food allergies. Conducting food trials and recording observations of the progression of these clinical signs can be extremely time consuming for the owner. Therefore, technicians must stress the importance of identifying the cause of the food allergy. Once the allergen has been successfully identified, a new diet can be implemented so that the pet can live a comfortable and healthy life.

    1. Roudebush P, Guilford WG, Shanley KJ: Adverse reactions to food, in Hand MS, Thatcher CD, Remillard RL, Roudebush P (eds): Small Animal Clinical Nutrition, ed 4. Topeka, KS, Mark Morris Institute, 2000, pp 431-453.

    2. Kennis R: Use of atopic dogs to investigate adverse reactions to food. JAVMA 221:638-640, 2002.

    3. Leistra MHG, Markwell PJ, Willemse T: Evalua­tion of selected-protein-source diets for management of dogs with adverse reactions to foods. JAVMA 219(10):1411-1414, 2001.

    4. Rothstein E: How to diagnose and manage adverse food reactions. Proc Tufts Anim Expo 2002.

    5. MacDonald JM: Food allergy, in Griffin CE, Kwochka KW, MacDonald JM (eds): Current Veterinary Dermatology. St. Louis, Mosby, 1993, pp 121-132.

    6. Scott DW, Miller WH, Griffin CE: Skin immune system and allergic skin diseases, in Muller & Kirk's Small Animal Dermatology, ed 6. Phila­delphia, Saunders, 2001.

    7. Reedy LM, Miller WH, Willemse T: Allergic Skin Diseases of Dogs and Cats, ed 2. Philadelphia, Saunders, 1997.

    8. Chalmers S, Medleau L: Recognizing the signs of feline allergic dermatoses. Vet Med 84:388, 1989.

    9. August JR: Dietary hypersensitivity in dogs: Cutaneous manifestations, diagnosis, and treatment. Compend Contin Educ Pract Vet 7:469, 1985.

    10. Carlotti DN, Remy I, Prost C: Food allergy in dogs and cats: A review and report of 43 cases. Vet Dermatol 1:55, 1990.

    11. Denis S, Paradis M: L'allergie alimentaire chez le chien et le chat. I. Revue de la literature. Méd Vét Québec 24:11, 1994.

    12. Denis S, Paradis M: L'allergie alimentaire chez le chien et le chat. II. Revue de la literature. Méd Vét Québec 24:15, 1994.

    13. Rosser EJ: Diagnosis of food allergy in dogs. JAVMA 203:259-262, 1993.

    14. Harvey RG: Food allergy and dietary intolerance in dogs: A report of 25 cases. J Small Anim Pract 33:22, 1993.

    15. White SD: Food allergy in dogs. Compend Contin Educ Pract Vet 20:261, 1998.

    16. White SD: Update on food allergy in the dog and cat. Proc World Small Anim Vet Assoc World Congr 2001.

    17. Beale KM: Adverse food reactions. Proc West Vet Conf 2004.

    18. White SD: Update on allergies: Food allergy. Proc Northeast Vet Conf 2004.

    19. Paterson S: Food hypersensitivity in 20 dogs with skin and gastrointestinal signs. J Small Anim Pract 36:529-534, 1994.

    20. Jackson HA: Food allergy and pruritic skin disease. Proc Brit Small Anim Vet Congr 2007.

    21. White SD, Sequoia D: Food hypersensitivity in cats: 14 cases (1982-1987). JAVMA 194:692-692, 1989.

    22. Rosser EJ: Food allergy in the cat: A prospective study of 13 cats, in Ihrke PJ, Mason I, Shite SD (eds): Advances in Veterinary Dermatology, vol 2. Oxford, England, Pergamon Press, 1993, pp 33-39.

    23. Guaguére E: Intolérance alimentaire í  manifestations cutanées: í propos de 17 cas chez le chat. Prat Méd Chir Anim Comp 28:451, 1993.

    24. Guilford WG, Markwell PJ, Jones BR, et al: Prevalence of food sensitivity in cats with chronic pruritus, vomiting, or diarrhea, in Kwochka KW, Willemse T, Von Tscharner C (eds): Advances in Veterinary Dermatology, vol III. Boston, Butter­worth Heinemann, 1998, p 493.

    25. Allenspach K: Food allergy in dogs — New insights. Proc ACVIM 2004.

    26. Halliwell REW: Diagnosing, treating, and preventing food allergies. Proc WSAVA Congr 2002.

    27. Crowe SE: Gastrointestinal food allergies: Do they exist? Curr Gastroenterol Rep 3(4):351-357, 2001.

    28. Allenspach K, Vaden SL, Harris TS, et al: Evaluation of colonoscopic allergen provocation as a diagnostic tool in dogs with proven food hypersensitivity reactions. J Small Anim Pract 47(1):21-26, 2006.

    29. Roudebush P, Cowell CS: Results of a hypoallergenic diet survey of veterinarians in North America with a nutritional evaluation of homemade diet prescriptions. Vet Derm 3:23-28, 1992.

    30. Lloyd D: Diagnosis and management of adverse food reactions in the dog. Proc World Small Anim Vet Assoc World Congr 2006.

    31. Simpson JW, Maskell IE, Markwell PJ: Use of a restricted antigen diet in the management of idiopathic canine colitis. J Small Anim Pract 35:233-238, 1995.

    32. Leib MS, Hay WH, Roth L: Plasmacytic-lymphocytic colitis in dogs, in Kirk RW (ed): Current Veterinary Therapy X: Small Animal Practice. Philadelphia, Saunders, 1989, pp 939-944.

    33. Roudebush P, Schick RO: Evaluation of a commercial canned lamb and rice diet for the management of adverse reactions to food in dogs. Vet Dermatol 5:63-67, 1995.

    34. Roudebush P, McKeever PJ: Evaluation of a commercial canned lamb and rice diet for the management of cutaneous adverse reactions to foods in cats. Vet Dermatol 42-, 1993.

    35. White SD: Food allergy and other skin diseases that respond to dietary management. Proc Canine Med Symp 2005.

    a

    Click to download a sample Diet History Form.

    bFor a sample food diary, see Roudebush P, Guilford WG, Shanley KJ: Adverse reactions to food, in Hand MS, Thatcher CD, Remillard RL, Roudebush P (eds): Small Animal Clinical Nutrition, ed 4. Topeka, KS, Mark Morris Institute, 2000, pp 444-445.

    References »

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