An Adverse Food Reaction is defined as an intolerance or allergy to one or more foods or additives, resulting in pruritus, skin lesions and gastrointestinal signs1.
Adverse food reactions include both non-immunologic (intolerance) and immunologic (allergic) mechanisms2 and in many cases, the exact mechanism remains unknown.
Food contains a variety of potential allergens and the protein content is the most likely source. Even when a dietary carbohydrate is linked to an allergic reaction, it is likely to be a protein allergen within the carbohydrate source2. Corn, for example, contains prolamine proteins (or maize zeins) which have been implicated in allergic reactions2.
Most food hypersensitivity reactions are considered to be type 1, caused by mast cell degranulation and subsequent inflammatory mediator release. To trigger an allergic response the IgE antibody and allergen complex adhere to the mast cell, causing degranulation. A release of histamine, prostaglandins and cytokines then occurs, resulting in the inflammation and associated clinical signs2. Type 4 cell-mediated hypersensitivity reactions have also been observed.
Both cutaneous and gastrointestinal signs can be seen as a result.
Clinical signs and prevalence of CAFR
Cutaneous Adverse Food Reactions (CAFR) are clinically indistinguishable from other causes of allergic skin disease such as flea allergic dermatitis (FAD) and atopic dermatitis (AD)4. The clinical signs of CAFR are non-specific and variable9 and non-seasonal pruritus is the key feature3,10.
Generalised pruritus is in dogs, with feet, pinna, and abdomen commonly affected10. The assumption that perineal pruritus is seen commonly in cases of CAFR was not observed in the recent literary review by Olivry and Mueller10. Perianal fistulas were also not reported as frequently as expected. In some individuals, otitis externa may be the only clinical sign.
Labrador Retrievers, Golden Retrievers, West Highland White Terriers and German Shepherds accounted for over 40 percent of cases in this review. Almost 40 percent of cases were noted in the medical records before one year of age10.
In cats, miliary dermatitis, symmetrical alopecia and eosinophilic granuloma complex have all been noted in cases of CAFR. Pruritus of the head and neck region was observed in half the feline cases reviewed in this study10.
Secondary bacterial or yeast infections are common in both species, and their presence can often complicate or delay diagnosis.
Diagnosis of CAFR
A recent study by Olivry and Mueller estimate that the prevalence of CAFR in dogs and cats with dermatological disease is about 5 percent9. Up to a third of cases of atopic dermatitis are estimated to have a food allergy component9. This emphasizes the value in offering an elimination-provocation trial in every case of suspected allergic skin disease.
The most reliable method to diagnose CAFR remains an elimination-provocation trial. Serological IgE testing has proven to be unreliable, which may be due to the possibility of type 4 cell-mediated reactions, but also due to false positives in control groups of normal animals confusing interpretation4. Serological testing is used for treatment with allergen-specific immunotherapy, but not considered diagnostic of CAFR or AD4.
The elimination phase should be maintained for at least five weeks in dogs and six weeks in cats- 80 percent of cases will see improvement and return to normal pruritus level in this time3,8. Confirmation of CAFR is then by reintroduction of suspected food items8. Reintroduction of each protein should be done individually to allow for any reaction to be noted. The recommended order for dogs includes beef, dairy products and chicken. In cats, the most common allergens are beef, fish and chicken5. A positive reaction following the re-challenge is considered to be the only valid method to confirm an allergen source5.
Options during the elimination phase include diets containing a novel protein source. This can be challenging due to the wide variety of protein sources many dogs and cats are now exposed to, as pet food companies expand their ranges. Home prepared diets can also be considered, again with a novel protein source. However, providing a balanced, complete home-cooked diet requires dedication, time and research, and many clients may find this option unrealistic for the time frame required3.
Prescription hydrolyzed diets (Royal Canin Anallergenic Dog / Cat and Hypoallergenic Dog / Cat) are preferable to either home-cooked or commercial ‘hypoallergenic’ diets2. Hypoallergenic diet, use of a novel protein to avoid an allergic response, is a misleading term. Many supermarket diets labelled as ‘hypoallergenic’ are not formulated under the strict conditions necessary to ensure no contamination of the protein source from other ingredients or equipment.
A hydrolyzed diet contains the protein source disrupted to reduce the proteins to molecules small enough to avoid recognition and mast cell degranulation. Methods to disrupt the proteins include using heat treatment, enzymatic hydrolysis and filtration2. This process should remove any antigens capable of triggering a subsequent immune response in a sensitized individual2.
The minimum size of molecule known to stimulate the IgE-mediated reaction is considered to be less than 10kDa, although the optimal size remains unknown2. In Royal Canin Anallergenic, 99% of the protein molecules are hydrolyzed down to less than 1kDa and 100% are below 3kDa.
Hydrolyzed diets also have a place in multimodal management of AD cases- latest research indicates in most cases of AD, multiple triggers cause pruritus, and this effect is additive4. If dietary management can limit exposure to some of those triggers, combined with other therapies, the allergen pressure may be relieved, and improvement in clinical signs will follow.
The ICADA guidelines7 recommend considering a food trial with a hydrolyzed diet if current management with dietary restrictions (home cooked or novel protein) is not controlling acute flare ups, perianal irritation or gastrointestinal signs.
Role of nutrition in CAD, CAFR and allergic skin disease
The role of nutrition in dermatological cases extends beyond elimination diets. Hydrolyzed diets have well-defined benefits in both the diagnosis and then management of CAFR which is the primary indication for Anallergenic and Hypoallergenic diets.
Hydrolyzed diets also have indications for use in AD where dietary control may lower the allergenic pressure to below the pruritus threshold and prevent further sensitization. An individual with AD has an increased predisposition to the development of allergies4. Use of Anallergenic and Hypoallergenic diets both prevents exposure to existing allergens and the development of future adverse reactions.
Percutaneous absorption of environmental allergens causing disease in animals with atopic dermatitis is well established4. This absorption of allergens increases with damage to the epidermal barrier. Canine AD cases have increasing evidence to suggest a defective skin barrier is present, similar to human AD4,6. Whether this is primary or secondary is still to be determined, but nutritional support can improve the skin barrier, reducing trans-epidermal water loss and limit the percutaneous absorption of environmental allergens4,5.
Key nutrients to improve the skin barrier, and support coat/hair regrowth in the diets include essential fatty acids (EFAs), zinc and a synergistic complex of antioxidants. EFAs have both a structural and functional benefit in dermatological disease. They act as precursors for prostaglandins and leukotrienes as well as maintaining the water permeability barrier and regulating epidermal proliferation11. EFA enriched diets provide higher amounts of EFAs than oral administration of supplements alongside a maintenance diet7.
Royal Canin Anallergenic and Hypoallergenic diets are clinically effective as well as cost effective compared to alternative nutraceutical preparations. They are an essential part of the clinical arsenal in battling chronic and frustrating dermatological cases.
Recommended products:
Royal Canin Anallergenic
Royal Canin Hypoallergenic
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References;
- Aufox E, May, E., Frank, L., Kania, S, (2018) PCR analysis of a prescription vegetarian diet and use in three dogs with cutaneous adverse food reactions Veterinary Dermatology 29:345-e122
- Cave, N. (2006) Hydrolyzed Protein Diets for Dogs and Cats Veterinary Clinics of North America Small Animal Practice 1251-1268
- Grant, D. (2018) Cutaneous Adverse Food Reactions Veterinary Practice available [online] at
https://veterinary-practice.com/article/cutaneous-adverse-food-reaction
- Marsella, R. and Benedetto, A., (2017) Atopic Dermatitis in Animals and People: An Update and Comparative Review Veterinary Science 4:37
- Mueller, R., Olivry, T. and Prelaud, P. (2016) Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats. BMC Veterinary Research 12:9
- Olivry, T. (2011) Is the skin barrier abnormal in dogs with Atopic Dermatitis? Veterinary Immunology and Immunopathology 144(11-16)
- Olivry, T et al (2015) Treatment of canine atopic dermatitis: 2015 updated guidelines from the International Committee on Allergic Disease of Animals (ICADA) BMC Veterinary Research 11:210
- Olivry, T., Mueller, R. and Prelaud, P. (2015) Critically appraised topic on adverse food reactions of companion animals (1): duration of elimination diets BMC Veterinary Research 11:225
- Olivry T., Mueller, R., (2016) Critically appraised topic on adverse food reactions of companion animals (3): prevalence of cutaneous adverse food reactions in dogs and cats BMC Veterinary Research 13:51
- Olivry, T and Mueller, R. (2019) Critically appraised topic on adverse food reactions of companion animals (7): signalment and cutaneous manifestations of dogs and cats with adverse food reactions BMC Veterinary Research 15:140
- Watson, T. D. G. (1998) Diet and Skin Disease in Dogs and Cats. The Journal of Nutrition 128:12
Postdate: 23rd April 2020