Signs of a food intolerance or allergy may include getting diarrhea after drinking a glass of milk, an itchy palate after eating apples, swelling in the face after consuming chicken eggs or a severe asthma attack due to peanut dust.

However, these symptoms are not just limited to people, because other mammals such as dogs, cats and horses may exhibit similar symptoms after feeding.

The number of pets affected by food allergies and intolerances has even converged with that of people. A working group of the European Academy of Allergy & Clinical Immunology focuses on this issue and recently published a position paper that sums up food intolerances and allergies in both animals and people, laying bare knowledge gaps.

Symptoms, triggers overlap

"Not only humans but basically all mammals are susceptible to developing allergies, as their immune system is capable of producing immunoglobulin E," lead author Isabella Pali-Schöll said. Normally, these special antibodies help defend parasites or viruses. At the same time, they are also responsible for type I allergy symptoms, which are the most well-known and immediately occurring symptoms and include hay fever, allergic asthma and anaphylactic shock. In the field of nutrition, there are also very common non-immunologic forms of food intolerance.

The position paper, primarily penned by Pali-Schöll and Erika Jensen-Jarolim from the interdisciplinary Messerli Research Institute of the University of Veterinary Medicine Vienna (Vetmeduni) and of the Medical University of Vienna in Austria, shows that the symptoms of food intolerance are similar in both animals and people.

In the case of dogs, cats or horses, however, the adverse reactions mostly affect the skin, followed by the gastrointestinal tract.

"Asthma or severe shock reactions have rarely been observed in animals," Pali-Schöll noted. There are even overlaps among the triggers of immune response to certain foods and ingredients. Pets may suffer from both lactose intolerance and outright milk protein allergies. Some mammals are also liable to allergic reactions from certain proteins in wheat, soy, peanuts, tree nuts, fish, eggs and meat.

Diagnostics underdeveloped

Precise knowledge about the active molecules of the allergens helps assess the risks of severe reactions, especially with food allergies. Many of these allergenic molecules that affect people have been identified and are already used in diagnostics, such as the so-called allergen microchip test.

As far as animals are concerned, there is still a big need for research, Vetmeduni said. Similarly, a precise and comprehensive diagnosis is essential for establishing adequate measures against food intolerance. However, many mechanisms and triggers for animals have not been sufficiently researched, in part because some test samples or substances are not even available.

A so-called elimination diet is the prerequisite for correctly diagnosing animals and humans. This regimen consists of removing all sources of protein from an animal's diet.

"During this period of diagnosis, the animal will be fed homemade food or diet food prescribed by a veterinarian. Only then, and if there have not been any dangerous allergic reactions before, can 'normal' food be gradually reintroduced," nutrition scientist Pali-Schöll advised.

This diagnostic procedure allows the allergen-free diet to be tailored to the respective food intolerance while avoiding unnecessary restrictions. A thorough comparison of adverse food reactions in people and animals offers insight into the risk factors for the development of the condition and can, thus, lead to improved recommendations for the prevention and treatment of adverse food reactions in animals and people. At the moment, there are no therapies for humans and animals, but many new variants of immunotherapy have entered the trial phase.

"As for the so-called sublingual and epicutaneous immunotherapy, which is treatment under the tongue or on the skin, respectively, the first few trial phases have already achieved some success, but it will take several more years for any products to see market launch and standard application," Pali-Schöll said.

The Messerli Research Institute was founded in 2010 with support from the Messerli Foundation, under the management of Vetmeduni and in cooperation with the Medical University of Vienna and the University of Vienna. The research is devoted to the interaction between humans and animals, as well as its theoretical principles in animal cognition and behavior, comparative medicine and ethics. Its work is characterized by its broad interdisciplinary approach (biology, human medicine, veterinary medicine, philosophy, psychology and law) and strong international focus.