Update on Knowledge of Food Allergies in Dogs and Cats

At the last World Congress of Veterinary Dermatology, which took place in Boston last July, our colleague, veterinary dermatologist Hilary Jackson, provided a comprehensive update on new developments in dog and cat food allergies.

Introduction

Atopic dermatitis in dogs is a complex skin disease whose incidence is significantly increasing, particularly in urban areas. This skin pathology, considered a genetic disease in certain predisposed breeds such as the Golden Retriever and the Shar Pei, requires a thorough understanding of its pathophysiological mechanisms. Canine atopic dermatitis, common in dogs, often involves a dietary component whose characterization has been considerably enriched in recent years thanks to major scientific advances.

Pathogenesis and Immunological Mechanisms

Genetic and Environmental Factors

Atopic dermatitis is a multifactorial disease with known genetic predisposition. Studies show that the majority of affected animals have a family history of atopic diseases. Increasing urbanization also plays a significant role in the rising incidence of this condition, highlighting the importance of environmental factors in its development.

Role of the Skin Barrier and Allergen Exposure

The integrity of the skin barrier is a crucial element in the pathogenesis of the disease. An alteration of this barrier facilitates the penetration of allergens, whether dietary or environmental. Allergen exposure can occur orally but also percutaneously, especially when the skin barrier is damaged. This fundamental discovery explains why some animals can develop sensitization to food proteins by simple skin contact.

Influence of Allergen Type and its Transformation

A fundamental aspect recently highlighted concerns the impact of food processing on its allergenic potential. Studies show that the method of preparation significantly influences the antigenicity of proteins. This discovery is particularly well illustrated in the case of peanuts, where cooking substantially modifies the presentation of protein epitopes. Roasted peanuts thus have a higher allergenic potential than boiled peanuts, highlighting the importance of food processing in the development of allergies.

Central Role of the Gut Microbiome

Intestinal dysbiosis is emerging as a determining factor in the pathogenesis of atopic dermatitis and food allergies. Recent research shows that a disturbance of the intestinal flora during the first three months of life can significantly predispose to the development of allergies. This critical period not only influences overall susceptibility to allergens but also determines the specificity of future allergic responses.

Studies conducted in dogs, particularly in beagles predisposed to atopic dermatitis, reveal that early administration of probiotics can delay the onset of clinical signs and mitigate their severity. Controlled atopic dermatitis is accompanied by a diversification of the skin and intestinal flora, highlighting the importance of the gut-skin axis in the pathogenesis of the disease.

Clinical Picture and Manifestations

Food allergy represents a significant clinical phenomenon in veterinary dermatology, with varying prevalence according to scientific studies. Epidemiological data show that among dogs with allergic disorders, the percentage of dogs affected by food allergy ranges between 8% and 62%.

More specifically, among all allergic dogs, 25% to 49% are affected by food allergies. This significant variability is explained by several methodological factors, such as differences in study protocols, dog populations studied, diagnostic criteria used, and allergy detection methods.

Clinical Expression in Dogs

Atopic dermatitis associated with food allergy manifests itself through a varied clinical picture. Pruritus is the cardinal sign, with a particular predilection for certain anatomical areas such as the paws, where excessive licking can lead to lesions resembling human eczema. Facial inflammation, particularly observable in predisposed breeds like the Golden Retriever or Shar Pei, represents a characteristic sign.

Secondary complications play a major role in the evolution of the disease. The proliferation of Malassezia pachydermatis and the development of pyoderma can considerably worsen the initial clinical picture. Perianal pruritus, although not specific to food allergy, is a frequent clinical sign, even in the absence of anal sac disease.

Feline Peculiarities

In cats, clinical manifestations present certain specificities. The eosinophilic granuloma complex can affect different locations, including the head, skin, paw pads, and even inside the oral cavity. Symmetrical alopecia, mainly ventral but able to extend to the flanks and limbs, is a characteristic sign. Extra-cutaneous manifestations, such as conjunctivitis or respiratory disorders, require particular attention during clinical evaluation.

Temporality of Clinical Manifestations

The chronology of symptom onset is of major diagnostic importance. Prospective research demonstrates significant variability in the speed of appearance of clinical signs. In the context of IgE-mediated reactions, an in-depth study conducted on Maltese beagles identified a precise temporal sequence. The first manifestations occur within the first fifteen minutes in the form of erythema and redness, particularly localized around the head, ear flap, and conjunctiva. These initial manifestations progressively evolve, and after twenty-four hours, erythematous macules appear in the antebrachial folds. Progression can continue for two weeks, sometimes leading to the development of superficial pyoderma on the ventral abdomen.

Diagnostic Approach

Initial Clinical Evaluation

The diagnosis of food allergy in the context of atopic dermatitis requires a rigorous methodical approach. A detailed anamnesis forms the basis of the investigation, with particular attention paid to the age of symptom onset. Early manifestation, especially before twelve months, strongly suggests a predominant dietary component. This observation is particularly true in cats, where approximately 27% of cases manifest before one year of age.

Specificity of Diagnostic Tests

Complementary examinations, including blood tests for the dosage of food-specific IgE, must be interpreted with extreme caution. Epicutaneous tests, developed notably by Professor Ralf Mueller, show interesting results but require rigorous methodology. The food allergen must be applied and maintained on the skin for 48 hours, which requires wearing a specific protective device. Negative results from these tests are more reliable than positive results for selecting tolerated foods.

Lymphoproliferation Tests and New Approaches

Lymphocyte proliferation or blastogenesis tests represent a promising diagnostic approach, although not yet routinely available. This technique relies on the collection and culture of patient lymphocytes in the presence of specific food stimuli. The observation of lymphocyte proliferation and the production of cytokines like interleukin 2 after 24 to 48 hours of incubation suggest prior sensitization. Nevertheless, the need to maintain cell viability is a major technical constraint currently limiting its clinical application.

Therapeutic Strategy

Elimination Diet: Cornerstone of Treatment

The elimination diet remains the diagnostic and therapeutic gold standard. Its optimal duration, established by rigorous clinical studies, varies depending on the species concerned. In dogs, 85% of subjects show significant improvement after five weeks, while in cats, eight weeks are necessary to observe a favorable response in 90% of individuals. A total period of twelve weeks is essential to ensure maximum effectiveness of the protocol.

Anti-inflammatory Management

The judicious use of anti-inflammatories during the first weeks of the elimination diet significantly facilitates therapeutic compliance. Prednisolone or oclacitinib can be administered for three to four weeks, followed by a two-week withdrawal period before any food challenge. This therapeutic window allows for objective evaluation of the response to the elimination diet, with sustained improvement during this period strongly suggesting a dietary component.

Choice of Diet

The selection of the diet requires particular attention. Hydrolyzed proteins have the theoretical advantage of reduced allergenicity, but some animals may nevertheless develop reactions even to these modified proteins. Cross-reactivity studies have revealed unexpected structural homologies between different protein sources. For example, lactate dehydrogenase, a ubiquitous enzyme, shows similarities greater than 85-90% between species as diverse as ostrich, alligator, pork, horse, and rabbit.

Food Challenge Protocol

Food challenge is a crucial step in confirming the diagnosis. The most recent studies reveal remarkable variability in the timing of reactions. Prospective data show that 23.6% of dogs react within three to six hours of exposure, while 60.9% react within the first twelve hours. This observation is of paramount importance for post-challenge clinical monitoring.

The amount of allergen required to trigger a reaction varies considerably across individuals. Rigorous clinical observations demonstrate that a single teaspoon of food can be enough to provoke a reaction in certain particularly sensitive subjects. The phenomenon of cumulative dose, well-documented, highlights that repeated exposure even to small doses can ultimately trigger a significant clinical reaction.

Clinical manifestations during the challenge generally follow a characteristic temporal sequence. Erythema and periorbital inflammation can appear within the first fifteen minutes. Truncal inflammation typically develops within twenty-four hours, while superficial ventral pyoderma can manifest after two weeks of exposure.

Long-Term Therapeutic Management

The therapeutic approach must adapt to each patient’s specificities. Longitudinal studies reveal that some animals may experience spontaneous resolution of their food allergy, particularly young subjects. This phenomenon is observed especially in the context of “atopic march,” where early food allergies may attenuate while environmental sensitizations develop later.

Managing dietary indiscretions is a major challenge in therapeutic follow-up. The occasional administration of anti-inflammatories may be necessary during involuntary transgressions of the diet. This pragmatic approach helps maintain a satisfactory quality of life while preserving the overall effectiveness of management.

Cross-Reactivity and Therapeutic Implications

In-depth study of cross-reactivity phenomena has revealed complex interactions between different protein sources. The presence of antibodies directed against mealworm proteins and storage mite allergens in the serum of dogs, both healthy and atopic, demonstrates the existence of significant cross-reactions. Studies on lactate dehydrogenase, a ubiquitous enzyme in mammalian tissues, have highlighted remarkable structural homologies between phylogenetically distant species. These discoveries raise crucial questions regarding the selection of alternative proteins in elimination diets.

Peculiarities of Therapeutic Response

Clinical observations demonstrate significant variability in the evolution of the disease among individuals. The phenomenon of “atopic march” is characterized by a dynamic progression of allergic manifestations. Young animals initially presenting with food allergy may subsequently develop environmental sensitizations, while their food reactivity gradually attenuates. This natural evolution directly influences long-term therapeutic strategies.

Conclusion

The deep understanding of the pathogenesis of food allergies in the context of atopic dermatitis has evolved considerably in recent years. Major advances include the characterization of immunological mechanisms, the importance of the skin barrier, and the crucial role of the intestinal microbiome. The complexity of interactions between these different factors highlights the need for a personalized and multifactorial therapeutic approach.

Frequently Asked Questions

1. What is the optimal duration of an elimination diet depending on the species? The optimal duration varies by species: in dogs, 85% of subjects show significant improvement after five weeks, while in cats, eight weeks are needed to observe a favorable response in 90% of individuals. A total period of twelve weeks ensures maximum efficacy of the protocol.

2. What is the real significance of serological tests in the diagnosis of food allergies? Clinical studies demonstrate the significant limitations of specific IgE assays. This situation is explained by the complexity of the immunological mechanisms involved and the structural modifications of proteins during food processing. Serological reactivity does not necessarily predict a clinical manifestation, highlighting the paramount importance of the elimination diet as the gold standard diagnostic tool.

3. How to interpret reaction times during food challenges? Prospective data reveal a variable chronology of reactions. The critical period is within the first twelve hours for 60.9% of dogs, with a significant subgroup (23.6%) showing early reactions within three to six hours. This temporal variability requires adapted monitoring during food challenges.

4. What is the importance of the gut microbiome in the pathogenesis of food allergies? Recent research demonstrates the crucial role of early intestinal dysbiosis, particularly during the first three months of life, in the subsequent development of allergies. The administration of probiotics to predisposed puppies can favorably influence the evolution of atopic dermatitis, highlighting the potential therapeutic importance of microbiome modulation.

5. How to explain the variability of long-term clinical evolution? The phenomenon of “atopic march” illustrates the dynamic evolution of allergic manifestations. Young animals initially presenting with food allergy may experience spontaneous symptom attenuation, while environmental sensitizations gradually develop. This natural evolution guides the adaptation of long-term therapeutic strategies.

Future Perspectives

Recent advances in understanding immunological mechanisms and the role of the intestinal microbiome open promising therapeutic perspectives. The in-depth characterization of cross-reactivity phenomena will allow for refining food avoidance strategies. Early identification of at-risk subjects and the development of targeted preventive interventions are priority research areas for optimizing the management of this complex condition.