Dermatological symptoms vary widely from generalised pruritus, localised pruritus, otitis externa (mostly chronic), skin florescences on the croup or all other localisations, and pododermatits. The symptoms of the gastrointestinal tract usually resemble chronic inflammatory bowel disease, with vomiting, diarrhoea and frequent defecation being prominent. Of course, not all symptoms need to be present to diagnose a food allergy. Some dogs tend to have more skin florescences, others only suffer from chronic otitis, and still others only show variable faecal consistency with frequent defecation. Thus, a pure skin or a pure gastrointestinal symptomatology can occur.
Symptoms: What are the main clinical symptoms of food allergy? Can pure skin symptoms or pure gastrointestinal symptoms occur?
Symptoms: A cat has ulcerative itchy skin lesions, especially in the head/neck area - can this also be food-related?
Yes, because cats in particular usually react with efflorescences in the face and neck area if this is due to a food allergy. The strong itching leads to excoriations, which can manifest themselves as ulcerative skin changes. But all other reaction patterns of the cat can also occur. Cats use their rough tongues to “scratch”. As a result, itching in cats usually manifests itself in increased grooming, by licking or gnawing the skin. The consequences are alopecia, although the skin on these naked parts of the body is usually completely intact. Another clinical manifestation would be the so-called “miliary dermatitis”, whereby one notices many small crusts scattered over the back when stroking the animal. The expression of the “eosinophilic granuloma complex” can also be food-related; in this case, ulcers are often seen on the lips, raised skin lesions mostly on the abdomen or a strip-shaped skin change on the hind extremities. Particularly in cats that are allergic to a food, deep scratch marks in the head area (excoriations) are often seen, which the cat has inflicted on itself due to the massive itching.
Diagnostics: How is the diagnosis of feed allergy made lege artis and what is meant by the "golden standard"?
Just like the classic allergy (atopic dermatitis), feed allergy is also a clinical diagnosis. A detailed anamnesis supports the diagnosis, which is clearly substantiated by an elimination diet (= exclusion diet) with subsequent provocation samples.
The serological feed test is used to select a protein and a carbohydrate, which were negative for both antibodies in the allergy test, for the elimination diet. The test is also very helpful in terms of owner compliance. However, it does not diagnose the allergy, but is used for allergen selection. The “golden standard” is always the elimination diet followed by the provocation diet.
Diagnostics, IgE/IgG: What difference does the IgE or IgG determination in the serological feed allergy test provide?are both clinically relevant? How should the result be interpreted if only one fraction is elevated?
In the case of classical allergies (IgE-mediated, immediate reaction), the symptoms appear relatively shortly after ingestion of food; this makes it possible to establish a direct link to the food. In the case of IgG-mediated allergies (late reactions), the diagnosis is more difficult because the symptoms often only appear after a few days, and the direct link to the food can therefore no longer be clearly established. IgE antibodies react very quickly and represent the immediate reaction of the immune system. IgG antibodies are associated with the delayed reaction, but both are clinically relevant, and the difference IgE versus IgG-mediated is often clinically indistinguishable. A positive result should be interpreted for both IgE and IgG, and the animal should eventually be put on an elimination diet containing only ingredients that test negative for both IgE and IgG.
Diagnosis: A cat that has been treated many times with typical skin symptoms that are clearly caused by a food allergy is negative in the conventional serological food allergy test.
What could be the cause of this?
One reason for this may be that the animal has been pre-treated with cortisone depot preparations against the strong itching, which can of course strongly change the result of the allergy test (up to 3 months!). Furthermore, it is possible that the animal suffers from a non-immune food intolerance, which cannot be diagnosed with the conventional serological food allergy tests. In this case, the diagnostic tool of choice is an elimination diet. However, it could also be that the animal is currently on an elimination diet and therefore no allergen contact is taking place. In such cases, the test will give false negative results. For this reason, it is recommended to always perform the Sensi test BEFORE starting a therapeutic diet.
Only one protein and one carbohydrate source should be used at a time. After a 2-month diet, a new allergen can be added to the food every 14 days.
Elimination diet: Can vegetables and fruit be fed in case of food allergy and if so which varieties?
In principle, no fruit and vegetables should be fed during an elimination diet. A particular problem here is protein-rich vegetables such as beans or soya, as they contain pure protein and can therefore in principle be handled in the same way as meat.
By means of provocation diets, vegetables or fruit (always only one allergen every fortnight) can then gradually be tested additionally. The greater danger, especially for atopics who are also allergic to food, is that cross-reactions can occur, especially between pollen and fruit (e.g. birch pollen and apples or carrots) – also known as OAS (oral allergy syndrome). Birch pollen is very interesting in this respect because it can trigger the “fresh fruit syndrome”. This is a strong cross-reactivity between birch pollen and fruits (especially apples) and various vegetables. Accordingly, in the case of a pure food allergy, vegetables with a high protein content should not be fed. In patients who also suffer from atopy, however, one must always be aware of these cross-reactions.
Elimination diet: Over what period should it be carried out at least in order to be able to assess success?
In order to be conclusive, an elimination diet should be followed for at least 8 weeks (in rare cases even longer is necessary, but after 2 months at least an improvement of the symptoms can be seen). The provocation tests to be carried out afterwards would be just as necessary, as this method is the “golden standard” for clearly diagnosing a feed allergy. However, there is usually the problem that the owner is happy that his animal is finally symptom-free and therefore does not want to expose it to further experiments.
In a hydrolysed diet, the allergenic structures are broken down into their individual components and in this form are not recognised by the immune system as a whole allergen. In addition to proteins (e.g. meat, fish), carbohydrate sources (rice, soy, etc.) can also be hydrolysed in the feed. However, there are also animals that react to these hydrolysed allergens, so unfortunately there is no 100% guarantee here either.
Diet: What alternative carbohydrate sources are available if my pet is allergic to conventional carbohydrates?
Here, it is advised to resort to alternative carbohydrate sources, e.g. in well-stocked food markets or from health food stores. Examples are: Quinoa, amaranth, millet, buckwheat (these 4 are also gluten-free), cassava (tapioca), pumpkin, sweet potato, yams, tapioca.
Attention – spelt, green spelt, emmer, durum, kamut, khorassan, einkorn, bulgur are all subspecies of wheat! Spelt is tolerated by some wheat allergy sufferers, but there is no 100% guarantee.
Diet: A patient was fed reindeer and potato for years and tolerated it well, but now there is a suspicion that he might be allergic to them too. Is this possible?
There are, of course, allergy sufferers who need to change and adapt diets because new allergen contact can cause new sensitisations to develop. It is therefore quite possible that a patient can no longer tolerate a diet that has worked for years from one moment to the next.
Diet: Despite the commercially available hypoallergenic diets, it is not possible to get the dog symptom-free.
Could it be that he also reacts allergically to these hypoallergenic foods?
Yes, this is quite possible, as there are allergy sufferers who cannot tolerate commercial diets in principle. This can also be due to storage, production, etc. Among other things, storage mites play a role. For these patients, it makes sense to switch to a home-cooked diet (e.g. horsemeat and potato). In addition, there are now some studies that prove that commercial feed can be contaminated with foreign allergens.
Feed intolerance: Can it also be detected by means of a feed allergy test? How should I proceed in case of suspicion?
As feed intolerance is not antibody-mediated, it cannot be detected with the conventional serological feed test. If suspected, the animal should therefore always undergo an elimination diet. The mechanisms of feed intolerance are complex: feed poisoning (toxins in the feed), pharmacological intolerance (e.g. chocolate poisoning), pseudoallergic mechanisms (histamine-mediated: high histamine content in the feed), metabolic reactions (lactose intolerance), feed idiosyncrasy (similar to feed allergy, but no immunological mechanism, e.g. feed additives) and intolerance to disaccharides may play a role. A classic feed allergy, on the other hand, is antibody-mediated and the allergens can be detected via serological tests.
FAQ = frequently asked questions
ASIT = Allergen-specific immunotherapy (new) = Hyposensitisation (old)
RK = reaction class