Diagnosing adverse food reactions in canine and feline patients
Understanding the clinical picture and performing appropriate diet trials will improve identification of patients suffering from food reactions, including allergy
Adverse food reactions (AFR) occur in canine and feline patients, and commonly present with cutaneous or gastrointestinal clinical signs. AFRs encompass true food allergies, where the immune system is involved in a hypersensitivity reaction, and food intolerances, which lack direct involvement of the immune system, and can occur for metabolic reasons, toxins, or be idiosyncratic. It can be difficult to distinguish between intolerances and allergies due to similar clinical signs, inciting foods, and response to treatment.
Ultimately, recognizing and diagnosing an AFR in a dog or cat requires the veterinarian to recognize the clinical picture and perform a dietary elimination trial followed by food challenge. At the Fetch dvm360® conference in San Diego California, Jennifer Aniya, DVM, DACVD of the Pet Emergency and Specialty Center in San Diego, discussed tips to appropriately recognize patients suffering from adverse food reactions.
There is no age or gender predilection to AFRs. A recent review found that German Shepherd dogs, Labrador Retrievers, Golden Retrievers, and West Highland White Terriers accounted for 4 of 10 affected dogs.1 This review also found that dogs tend to present with clinical signs at a younger age than cats, with 40% of dogs developing cutaneous clinical signs by age 1 year, while cats had a mean age of onset of 3.9 years.1
Cutaneous clinical signs are common in both dogs and cats with AFRs. Pruritus varies in its distribution, but most commonly includes generalized pruritus in dogs and face, head, and neck pruritus in cats.2 Aniya notes that while the ears, paws, and the abdomen are commonly affected sites in dogs, some patients may present with only otitis externa and perianal pruritus. “The most common reported cutaneous manifestation of AFR are recurrent bacterial and yeast skin infections, otitis externa, and atopic dermatitis” in dogs, Aniya noted. All of these may be present in the same patient. In addition to the “ring around the collar” pattern of pruritus seen in cats, they “can also present with self-induced alopecia, military dermatitis, [and] eosinophilic skin lesions such as eosinophilic granulomas, plaques, and indolent ulcers,” Aniya added.
Gastrointestinal signs are also common in patient with AFRs. Aniya noted that various studies have shown dogs suffering from an AFR will have concurrent gastrointestinal and cutaneous clinical signs in 6-44% of cases.Diarrhea and increased numbers of bowel movements daily are the most common gastrointestinal signs in dogs. Additional clinical signs may include vomiting, changes in stool consistency, halitosis, borborygmus, flatulence, inflammatory bowel disease, anal gland impaction, and coprophagia in dogs. Cats are more likely to present with vomiting than dogs, though diarrhea is the most common clinical sign in this species as well.3
Dietary Elimination Trials
“There have been many tests developed to help diagnose food allergy,” Aniya noted. “But the consensus remains that a dietary trial followed by dietary provocation is the most effective method of diagnosis.” Commercially available, prescription diet options for elimination trials include hydrolyzed and novel protein diets.
Hydrolyzed diets are formulated to contain amino acids and peptides less than 10 kDa, which is the size of allergenic proteins that trigger mast cell activation in humans with AFR. These diets vary in their protein source and the size of the peptides (measured in kDa) in each formula. Aniya noted that advantages of hydrolyzed diets “include nutritionally balanced formulas, generally good palatability, and formulations for growth, maintenance, and other medical disorders [with multi-function formulations].” Disadvantages of hydrolyzed diets include price and variable palatability. Even in patients exposed to numerous protein sources prior to a diet trial, it is reasonable to expect these diets to be efficacious. However, there is a chance that a patient with an allergy to the parent protein will still react to the hydrolyzed diet.4
Novel protein diets are complete and balanced for diagnosis and maintenance. Aniya said she feels these diets also offer good palatability. However, due to the growing number of alternative protein sources available in over-the-counter diets, finding a truly novel protein for a patient may be difficult and new allergies can develop over time to the once novel protein. Additionally, these diets are rarely formulated for growth, making them inappropriate for young patients. Aniya also advised veterinarians that there is rising concern for the potential of cross-reactivity between food allergens, which could lead to a veterinarian ruling out a food allergy based on nonresponse to a novel protein, when in fact the patient is cross-reacting. In 1 study, 9 cross-reactive Ig-E binding allergens were present in chicken, white fish, and salmon.5
Historically, literature has suggested an 8-week elimination diet was needed for over 90% of dogs and cats with AFRs to achieve remission.6 However, obtaining strict client compliance to a diet trial for this period is difficult. A recent study evaluated if a short-course of prednisolone administered in the early stages of an elimination diet could shorten the overall diet trial duration.7 This study found that diet trial duration was reduced by 2 to 4 weeks with the use of low-dose prednisolone in dogs.
Aniya reminded veterinarians that fleas, yeast, superficial pyoderma, and other factors that cause pruritus should be controlled during the diet trial. Gastrointestinal signs generally improve within 2 weeks, but cutaneous clinical signs can take longer. Aniya recommends rechecking patients 2- to 4-weeks into the diet trial to assess the presence of secondary infections, monitor pruritus and other clinical signs, and assess owner compliance.
Take Home Points
Adverse food reactions in dogs and cats can be frustrating for pet owners and veterinarians. Recognizing common clinical signs and starting diet trials with either a novel protein or hydrolyzed diet are important to obtaining an accurate diagnosis. Recent evidence suggests low-dose prednisolone use at the beginning of the diet trial may shorten the length of the diet trial in dogs. In some patients, multiple diet trials may be necessary if a patient has an allergy to the parent protein of a hydrolyzed diet or cross-reactivity to the novel protein source.
Kate Boatright, VMD, a 2013 graduate of the University of Pennsylvania, is a practicing veterinarian and freelance speaker and author in western Pennsylvania. She is passionate about mentorship, education, and addressing common sources of stress for veterinary teams and recent graduates. Boatright is also actively involved in organized veterinary medicine at the local, state, and national levels.
- Olivry T, Mueller RS. Critically appraised topic on adverse food reactions of companion animals (7): signalment and cutaneous manifestations of dogs and cats with adverse food reactions. BMC Vet Res; 2019:15(1):140. doi:10.1186/s12917-019-1880-2
- Ravens PA, Xu BJ, Vogelnest IJ. Feline atopic dermatitis: a retrospective study of 45 cases: (2001-2012). Vet Dermatol. 2014;25(2):95-102. doi:10.1111/vde.12109
- Gaschen FP, Merchant SR. Adverse food reactions in dogs and cats. Vet Clin Small Anim. 2011;41(2):361-379. doi:10.1016/j.cvsm.2011.02.005
- Bizikova P, Olivry T. A randomized, double-blinded cross-over trial testing the benefit of two hydrolysed poultry-based commercial diets for dogs with spontaneous pruritic chicken allergy. Vet Derm. 2016;27(4):289-e70. doi:10.1111/vde.12302
- Bexley J, Kingswell N, Olivry T. Serum IgE cross-reactivity between fish and chicken meats in dogs. Vet Derm. 2018;30(1):25-e8. doi:10.1111/vde.12691
- Olivry T, Mueller RS, Prelaud P. Critically-appraised topic on adverse food reactions of companion animals (1): duration of elimination diets. BMC Vet Res. 2015:11:225. doi:10.1186/s12917-015-0541-3
- Favrot C, Bizikova P, Fischer N, Rostaher A, Olivry T. The usefulness of short-course of prednisolone during the initial phase of an elimination diet trial in dogs with food-induced atopic dermatitis. Vet Derm. 2019;30(6):498-e149. doi:10.1111/vde.12793