Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats

Background To diagnose cutaneous adverse food reactions (CAFRs) in dogs and cats, dietary restriction-provocation trials are performed. Knowing the most common offending food allergens for these species would help determining the order of food challenges to optimize the time to diagnosis. Results The search for, and review and analysis of the best evidence available as of January 16, 2015 suggests that the most likely food allergens contributing to canine CAFRs are beef, dairy products, chicken, and wheat. The most common food allergens in cats are beef, fish and chicken. Conclusions In dogs and cats, after a period of dietary restriction leading to the complete remission of clinical signs, food challenges to diagnose CAFR should begin with beef and dairy products, the most commonly recognized food allergens in these two species.


Background
The diagnosis of cutaneous adverse food reactions (CAFRs) in dogs and cats relies on the performance of dietary restriction-provocation trials. Knowing the most common offending allergens in these species would help determine which food challenges should be performed first to faster confirm the diagnosis of CAFR.

Clinical scenarios
You have two patients: The first is a 1-year-old male Labrador retriever with a 3-month history of pruritus and recurrent mucous diarrhea. This dog has been eating a commercial diet for the last 6 months. On physical examination, you do not detect anomalies besides soft stools on rectal palpation. Your second patient is a 2-year-old female spayed Persian cat that has been scratching her face for the last year. This self-trauma only responds partially to high dose of prednisolone. Physical examination reveals the cat to be thinner than expected and to have excoriations on the head and neck. You suspect that both patients could be reactive to their commercial diets, but you wonder which one of the ingredients listed on the labels would be the most likely sources of allergens.

Structured question
In dogs and cats suspected of CAFR, which food sources are most often reported to induce clinical signs after challenge?

Search strategy
The CAB Abstracts and Web of Science (Science Citation Index Expanded) databases were searched on January 16, 2015, using the following string: ((dog or dogs or canine) or (cat or cats or feline)) and (food or diet*) and (allerg* or atop* or hypersens* or intolerance). The search was limited to the period 1985 to 2015. Bibliographies of identified articles were then further searched for additional relevant reports.
There were several limitations in interpreting the data presented. In most studies details of the provocation with individual allergens were not provided. Furthermore, most reports only listed allergens associated with a deterioration of signs upon rechallenge, but not those associated with negative provocations; this could possibly bias the estimation of the prevalence of offending allergens. Only five studies had used a standardized rechallenge sequence in dogs [7][8][9][10]13]. In these studies, beef, chicken, wheat, soy and dairy products were the most common involved allergens, reflecting the data gathered from the literature. In cats, only one study attempted those uniform provocations [27], and beef, fish and chicken were the allergens most commonly involved in that study. In addition the previous diet history was generally not provided, thereby preventing a clinically relevant interpretation of the data. Thus, the information gathered herein does not allow a true estimate of the prevalence of offending allergens nor any statement about the likelihood of positive provocations in relation to previously fed foods. Finally, the offending allergens found herein could merely reflect pet feeding habits in the preceding decades, and these allergens could change once new pet foods become fashionable and used more frequently.

Conclusion and implication for practitioners
In a dog living in Australia, Europe or North America, the allergens most likely contributing to CAFRs are beef, dairy products, chicken, wheat and lamb. As a result, these foods should be the first used for allergen provocation for CAFR diagnosis. In cats, the most common allergens causing CAFRs are beef, fish and chicken.
Importantly, the identified evidence does not allow an estimation of the real prevalence of offending allergens in the population of dogs and cats with CAFR, as animals were usually only challenged with a small number of-but not all-allergens. As a result, the true prevalence of each offending allergens in dogs and cats is likely to be higher than that reported above. Importantly, all these estimates of prevalence will need to be reevaluated with prospective studies performing controlled rechallenges in a larger number of animals with a detailed history of their previous dietary exposure.

Competing interests
In the past three years, the three authors have lectured for, and received research funding and/or consulting honoraria from Royal Canin (Aimargues, France), which paid publication charges for this article.

Authors' contributions
The three authors selected the topic of this CAT. RSM performed the literature search, extracted and summarized the evidence. TO and PP verified the evidence and TO wrote the first draft of the article. The three authors edited and then approved the final manuscript.