Food Allergy in Dogs and Cats

Food allergies are part of adverse food reactions (food sensitivity) which are divided into two categories: immunological and non-immunological reactions.
Food allergy (food hypersensitivity) is described as all immune-mediated reactions following food intake. While, non-immune mediated reactions are indicated as food intolerance and among these:
food idiosyncrasy, food intoxication and food poisoning, anaphylactoid reactions to food and metabolic food reaction.
Impairment of the gastrointestinal defense predisposes patients to food allergy. In particular, impairment of the mucosal barrier and loss of oral tolerance are risk factors for the development of food allergy. The gastrointestinal tract has to differentiate between nutrients and potential harmful substances, like bacteria, viruses, parasites, which have to be tolerated and expelled respectively. The Gut Associated Lymphoid Tissue accomplishes this double function. Four mechanisms ensure the functions of tolerance and exclusion of antigens: the mucosal barrier, regulation of the immune response, elimination and tolerance of antigens reaching the mucosa.
In dogs and cats, Type I, Type III, and Type IV hypersensitivity are the most described immunologic mechanisms.
The Immediate hypersensitivity occurs within a few minutes until to several hours after ingestion of the food antigen. These responses are mediated by Ig-E bound on mast cells. Without oral tolerance, an individual develops an Ig-E response to a certain food antigen which binds on gastrointestinal and peripheric mast cells, leading to sensitization for the causative food antigen (type I hypersensitivity). On subsequent contact with the antigen, mast cell degranulation occurs, with release of inflammatory mediators, loss of fluids, alteration of motility and consequent vomiting, diarrhea. More general reactions occur when the antigen escapes from the gut and reaches sensitized basophils or Ig-E bearing mast cells in the skin. Extra-gastrointestinal effects are also possible only after the release of gastrointestinal mast cell mediators in the systemic circulation.
The Intermediate hypersensitivity occurs several hours after antigen ingestion and can be the result of a late-phase response to Ig-E mediated mast cell degranulation and/or type III hypersensitivity response to immune-complexes.
The Delayed hypersensitivity reactions in man appear several hours to 2–3 days after ingestion of the allergen and are probably mediated by Type III and Type IV reactions. The prevalence of these responses to food in the canine and feline population is unknown, but clinical experiences indicate their occurrence.
The capacity of a protein to induce an allergic reaction is influenced by the immunogenicity and the permeability of the gut for the protein. In man, food allergens are almost exclusively glycoproteins with a molecular weight of 10–70 kDa. In dogs and cats no data are available on the exact molecular weight of food allergens.
It seems, moreover, that allergenicity can be influenced by food processing and heat treatment: protein denaturation can destroy old epitopes, antigenic determinants, or expose new ones, with a decrease or increase of allergenicity respectively.
The exact prevalence of food allergy in dogs and cats remains unknown.
There is no breed, sex or age predilection, although some breeds are more commonly affected, such as: for the dogs Boxers, Spaniels, Collies, Dalmatians, German Shepherds, Lhasa Apsos, Miniature Schnauzers, Retrievers, Shar-Peis, Soft-Coated Wheaten Terriers, Daxhunds, West Highland White Terriers, while for cats Siamese and Birman are the breeds most commonly affected.
Food allergy is a non-seasonal disease with skin and or gastrointestinal disorders.
Affection of other organ systems occurs in man, but little in dogs and cats.
The most common symptom of food allergy is pruritus which is present constantly, but with variable intensity. Pruritus can be either generalized or limited to face, ears, paws, axillae, inguinal or perineal region. It is mostly corticoid-resistant.
In 20–30% of the cases, dogs and cats have concurrent allergic diseases such as atopy and flea-allergic dermatitis.
Gastrointestinal symptoms of food allergy are non specific: vomiting, diarrhea, abdominal pain or an increased fecal frequency can be seen.
Food allergy could have also a role in the following gastrointestinal diseases: Inflammatory Bowel Disease, Gluten-Sensitive Enteropathy in the Irish Setter, Protein-Loosing Enteropathy and Protein-Loosing Nephropathy in the Soft Coated Wheaten Terrier.
Up to now, a reliable diagnosis can only be made with elimination – challenge trials.
The first step is the introduction of an elimination diet through different options.
Novel Protein Diets: most of them are recommended for long term maintenance treatment for dogs and cats with food allergy, because they are supposed to be nutritionally complete and balanced. The lack of individual dietary history can explain why the diet was not effective in some of the dogs. The presence of additives in commercial foods or alteration of antigenic properties during food processing can be other possible explanations of the unsuccess of these diets.
Hydrolyzed Diets: hydrolysis of proteins to smaller peptides and amino acids reduces the molecular weight of the original protein, by which the antigenicity and allergenicity of the protein are reduced. This means that the molecules are too small to evoke a cross binding between Ig-E on the surface of the mast cell. This prevents degranulation of the mast cell and Ig-E mediated (Type I) hypersensitivity. Hence, it does not influence non-IgE-mediated forms of food allergy. Further clinical studies are required to evaluate the nutritional value and the efficacy of these diets in treating dogs and cats with food allergy.
The elimination diet must be then followed by a challenge test, challenging the patient’s former food. If symptoms, which were disappeared with the elimination diet, recur on the former diet, diagnosis of food allergy is made.
Because dogs and cats are exposed to a number of dietary proteins, it is very important to carry out extensive provocation tests with specific food components, to determine the allergen.
In conclusion, adverse food reactions are common condition with different clinical signs, including skin lesions and gastrointestinal symptoms. A systematic diagnostic and therapeutic approach focused on food trials, with elimination diet, challenge and provocation tests is required. Prognosis is generally excellent.