Adverse reactions to food in animals

Food intolerance reactions include any abnormal non-immunological response to a food and include toxicity, idiosyncratic reactions, pharmacological and metabolic reactions. Food-induced allergic dermatitis (FIAD) is defined as an exaggerated and anomalous immunological reaction to a food, which is not related to a physiological effect of any component of it.

The difficulty in distinguishing purely allergic reactions from food intolerance reactions leads to all these reactions being included under the common denomination of Adverse reactions to foods. Non-immunologically caused adverse reactions to food. The majority of dogs and cats with FIAD present cutaneous symptoms, whether accompanied or not by digestive signs, although the entry route for the allergen is intestinal. It is not very clear why some dogs and cats present cutaneous signs, others gastrointestinal signs and others a combination of the two, but there are several hypotheses.

Clinical signs

Food-induced allergic dermatitis (FIAD) is the allergy with the earliest presentation, with 48% of animals whose clinical signs start in their first year of life. The clinical signs of FIAD are the presence of non-seasonal itching and lesions associated with the severity of it or with the development of frequent secondary infections. The presence of itching in ears and perianal areas is very typical of FIAD, and in German shepherds a significant relationship has been seen between FIAD and the concurrent presence of otitis and perianal fistulas. The prevalence of otitis in the course of FIAD is very high, appearing in up to 80% of cases, and in 24% of cases otitis may be the only clinical manifestation. The clinical symptoms of a food allergy may be very similar to those of an atopic dermatitis, because they typically have the same clinical signs and affect the same areas: face, auricular pavilions, axillae, inguinal area and abdomen, so it becomes impossible to distinguish the two based on the clinical symptoms the animal presents. On the other hand, it has been proven that there is a significant relationship between the two, as there are animals that suffer from both allergies in percentages that range from 3 to 30% according to various studies.

In the case of felines, the clinical presentation may appear as non-seasonal generalised itching, eosinophilic granuloma complex, itching of the head and neck, miliary dermatitis, self-induced alopecia, exfoliative dermatitis and in some cases angioedema and urticaria.  


The only effective and valid test for diagnosing adverse reactions to foods is to carry out an elimination diet for 8 weeks and check for the disappearance of clinical signs in that time. Diagnosis will be performed after the recurrence of the clinical signs when the animal is exposed to the foods it ingested previously and their disappearance after returning to the hypoallergenic diet.

In terms of laboratory tests, from a blood sample we can find out whether our animal presents antibodies to allergens of animal or vegetable origin. The interpretation of the tests highlights that the negative has more predictive value, with 80%.


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