アレルギー性皮膚炎 : 犬の食物アレルギー (CARF)

• ペットの食餌に含まれる原因アレルゲン（もっとも頻繁に摂取する成分）の摂取に関連する非季節性のそう痒性アレルギー性皮膚炎
• ヒトが食物アレルゲンを摂食して死に至る場合があるのとは異なり、通常は生命を脅かす疾患ではない。
• 犬では正確な病因についてすべてわかっているわけではないが、多様な免疫学的反応（I型、III型、IV型、またはそのいずれか1つ）が関わっている可能性も考えられる。
• 最もよくみられるものは、食物中の糖タンパク質に対する異常な免疫反応である。糖タンパク質は通常、熱安定性、水溶性であり、大きさは10～70 kDaである。
• 犬ではアトピー性皮膚炎（AD）と併せて診断されることが多い（ADを除外しない）。
• 犬では、ノミアレルギー性皮膚炎およびアトピー性皮膚炎に次いで3番目に多いアレルギー性皮膚炎である（10～15%）。

• No age or sex predilection, but many cases begin at less than 1 year of age, and more common than AD in dogs younger than 6 months
• Any breed can be affected but reported predisposed breeds include: American cocker spaniel, English springer spaniel, Labrador retriever, collie, miniature schnauzer, Chinese shar pei, poodle, West Highland white terrier, boxer, dachshund, Dalmatian, Lhasa apso, German shepherd dog, Rhodesian ridgeback, pug, and golden retriever
• Distribution of clinical signs are similar to AD – face, ears, axillae, inguinal area, abdomen; pattern with pruritus of mainly ears and perineal area (“ears and rears”) is often attributed to CARF (24%)
• Concurrent gastrointestinal signs – 10-30%; flatulence and increased frequency of defecation occur more commonly than vomiting or diarrhea

• Recurrent secondary staphylococcal (pruritic or non-pruritic) dermatitis and yeast (Malassezia) infections can occur

• Rarely, vasculitis, urticaria and erythema multiforme

• Atopic dermatitis (non-seasonal)
• Sarcoptic mange
• Staphylococcal / Malassezia infections
• Cheyletiellosis
• Dermatophytosis
• Flea allergy dermatitis

• The only accurate method of diagnosis is a food trial that lasts up to 12 weeks during which time the pet’s clinical signs resolve (followed by recurrence of signs upon provocation—see below)
• This diet can be home-cooked or carefully selected prescription prepared food
• There is insufficient evidence that blood or skin testing for food allergies is diagnostic
• Ingredients must be novel proteins for the pet or hydrolyzed proteins (proteins broken down to peptides smaller than 10kDa)
• All treats, chewable medications (including parasite preventatives and NSAIDs) must be replaced with non-flavored versions or topical therapy where appropriate
• If pruritus resolves with the trial, a food challenge (provocation for up to two weeks) should be done to confirm the offending protein. This can be done with the initial diet, with ingredients from that diet, or specific treats. Once the offending protein is identified, avoiding its ingestion is the goal of long-term management.

• Once it is determined that the dermatitis is due to a reaction to something the pet has been fed, avoiding its ingestion is the goal of long-term management.
• Pruritus associated with CARFs generally has partial to no response to treatment with corticosteroids and/or cyclosporine (some animals show a partial response and then relapse when dose is tapered)

• Cross-reactions may occur among foods within a food group (e.g., beef and venison) and also between food allergens and other allergens (e.g., milk and beef; crustaceans and cockroaches; birch pollen may cross-react with a variety of fruits and vegetables) Beef has been reported as the most common reactant in dogs, followed by soy, chicken, milk, corn, wheat and eggs
• Hydrolyzed diets may work best for dogs with immediate (Type I) hypersensitivity reactions and may not work for dogs with delayed CAFR
• More than one elimination diet trial may be required to diagnose a CAFR
• If a home-cooked diet is used long-term consultation with a nutritionist is necessary to ensure the diet is nutritionally adequate for the patient

References:

• Bowlin, CL. Novel Proteins and Food Allergies. NAVC Clinician’s Brief. March 2010. pp 37-40.
• Bruet V, Bourdeau PJ, Roussel A, et al. Characterization of pruritus in canine atopic dermatitis, flea bit hypersensitivity and flea infestation and its role in diagnosis. Vet Dermatol. 2012; 23. 487-492.
• Bruner, S. Dietary Hypersensitivty, in Small Animal Dermatology Secrets, KL Campbell, 2004, pp 196-201.
• Gaschen, FP, Merchant SR. Adverse Food Reactions in Dogs and Cats. Vet Clin Small Animal. 41, 2011, pp 361-379.
• Handbook of Small Animal Practice, 5th ed. Morgan, RV, ed. 2008 pp 825-826.
• Jackson, H. Dermatologic manifestations and nutritional management of adverse food reactions. Vet Med. Jan 2007. pp 51-64.
• Kennis RA. Food allergies: update of pathogenesis, diagnosis and management. Vet Clin North Am Small Anim Pract. 2006; 35:175-184.
• Loeffler A, et al. A retrospective analysis of a case series using home prepared and chicken hydrolysate diets in the diagnosis of adverse food reactions in 181 pruritic dogs. Vet Dermatol. 2006, 17. pp 272-279.
• Martin A, et al. Identification of allergens responsible for canine cutaneous adverse food reactions to lamb, beef, and cow’s milk. Vet Dermatol. 2004, 15. pp 349-356.
• Miller, WH et al. Muller and Kirk’s Small Animal Dermatology, 7th ed. pp 397-404.
• Nett, C. Food allergy: new insights in the diagnosis and management. WCVD, 7/2012. pp 81-86.
• Olivry T, Bizikova, P. A systematic review of the evidence of reduced allergenicity and clinical benefit of food hydroylsates in dogs with cutaneous adverse food reactions. Vet Dermatol. 2010, 21. pp 32-41.
• Raditic DM, Remiilard, RL, Tater KC. ELISA testing for common food antigens in four dry dog food used in dietary elimination trials. J Animal Physiol Anim Nutrition. 2011. 95. pp 90-97.
• Ricci. R, et al. A comparison of the clinical manifestation feeding whole and hydrolyzed chicken to dogs with hypersensitivity to the native protein. Vet Dermatol. 2010, 21. pp 358-366.
• Williamson, NL. Chronic Skin Problems in a cocker spaniel. NAVC Clinician’s Brief. July 2008, pp 45-47.
• Zimmer A, et al. Food allergen-specific serum IgG and IgE before and after elimination diets in allergic dogs. Vet Immunol Immunopathol. Dec 15, 2011, 144(3-4), pp 442-447.