Allergy general

Atopic dermatitis: What are the main signs and how do I diagnose allergy?

The diagnosis of allergy is always a purely clinical diagnosis resulting from a thorough history (age, race, seasonality) and the appropriate clinical examination.

The allergy test should only serve to identify the triggering allergens in order to then specifically avoid them or to be able to carry out an allergen-specific immunotherapy (ASIT, hyposensitisation). The main allergens are mites (house dust and storage mites), pollen (grass, herb and tree pollen), fungal spores and flea saliva (dog and cat) or insects (horse).

In dogs, atopic dermatitis is the second most common non-infectious skin disease. It manifests itself mainly between 6 months and 3 years of age and is accompanied by typical skin symptoms (primarily itching sine materia). The clinical picture of the cat is more similar to that of the horse than to the dog, and it often shows respiratory symptoms such as feline allergic bronchitis, asthma and rhinitis. However, dermatological lesions such as miliary dermatitis, self-induced alopecia, excoriations/ulcerations and clinical manifestations from the eosinophilic granuloma complex may also occur.

When should you have an allergy test?

For a seasonal allergy sufferer, in or shortly after the end of the season. For a year-round allergy sufferer who does not show seasonal fluctuations, the time of testing is irrelevant.

In the case of a new onset of symptoms, these should already exist for one month before an allergy test is carried out.

Sample material: Can material other than serum be sent in for the allergy test?

In principle, the test is validated for serum. But yes, you could also use lithium heparin or EDTA plasma, but serum is always best for determining the antibodies.

Sample age: Up to what period can I have a sample tested for allergies if it a) is frozen or b) has been in the refrigerator since collection?

As antibodies in frozen samples have a very long shelf life, it is no problem at all to repeat the allergy test up to 1 year later. However, it should be noted that after such a long time, the result obtained may no longer correspond to the current sensitisation status of the animal!

For samples that have been in the refrigerator (approx. 8-10°C) since collection, the antibodies should be examined within 4 weeks.

Pre-test: Is it necessary to do it or can you also start with the main tests right away?

No, the allergy pre-test (group test) is not mandatory.

If the clinical picture is appropriate, one can also start with the main tests (year-round and seasonal allergens). In this way, the result of the differentiation (determination of individual allergens) is available at the same time. This would have the advantage that in case of a positive result in combination with the clinical relevance, an ASIT could be requested immediately.

In many cases, however, the entry into allergy diagnostics via pre-testing represents the more cost-effective solution:

– This is due to the fact that often only one group tests positive, and the combination of pre-test + differentiation of one group is more cost-effective than the immediate differentiation (main test) of both groups.

– For animals that have been pre-treated with cortisone and it is not clear whether testing is already possible (with regard to the weaning period), it is advisable with regard to the costs to verify this for the first time via the pre-test.

– The pre-test also includes the single allergen flea saliva, which is not included in the main tests for seasonal and year-round allergens.

Pre-test positive: Why does a single allergen determination (differentiation) have to be carried out at all?
Would it not make sense to introduce a standard ASIT for year-round and/or seasonal allergens?

Every animal – just like every human being – reacts very individually to known allergens, especially in the case of an allergy. There are also studies that show that a “standard” ASIT, which contains the most common year-round or seasonal allergens, has significantly worse success rates (30%, placebo) than a solution that is individually tailored to the patient. Therefore, an individual allergen determination (differentiation) should always be carried out in order to be able to compile an individual ASIT suitable for the patient.

Pre-test with reaction class (RC) 1: Does it make sense to differentiate or carry out an ASIT?

Further differentiation of an RK 1 in the pre-test could yield a negative, but also a positive result (not predictable). However, if there is agreement with the clinic and the medical history, the implementation of an allergen-specific immunotherapy in the case of an RK 1 is certainly sensible. This is particularly advisable if the test result clearly correlates with the clinical symptoms and the medical history.

Corticosteroids: What are the withdrawal periods for topical, oral and depot corticosteroids?
Do these also apply to the feed tests?

Glucocorticoids are anti-inflammatory drugs that also have immunosuppressive effects depending on the dose. In allergy management, they are used in low anti-inflammatory doses to control inflammation and itching. Existing antibodies are not affected, but new formation may be reduced. We repeatedly see animals that show negative allergy test results due to the influence of cortisone. Weaning periods for corticosteroids apply to ALL allergy tests and therefore also to the feed test.

Recommended discontinuation periods:

– Local/topical corticosteroids: 2 – 4 weeks.
– Oral corticosteroids (e.g. prednisolone): up to 8 weeks
– Depot cortisone preparations (e.g. Voren®): up to 3 months

Every animal is different, so there are animals that receive Voren depot preparations for a long time and still have detectable antibodies, and there are animals that only receive eye drops containing cortisone and are negative in the allergy test.

Cortisone: Can I interpret a positive allergy test despite previous cortisone administration?
Does this also apply to a negative finding?

Yes, you can interpret a positive allergy result despite previous cortisone administration, but you should estimate the reaction classes somewhat higher. A positive result is always to be interpreted, in contrast to a negative result, as here the result is usually false-negative, and thus the allergens present could possibly not be recognised.

Oclacitinib: What should I be aware of when taking this medicine?

A few studies certify that Apoquel® has no influence on blood allergy tests. However, we repeatedly see animals that show a completely negative result in the allergy test when taking Apoquel®. Therefore, in case of doubt, a weaning period should be observed.

Mites: In the pre-test the mites are positive, which mites does the animal then have?

The mites determined in the pre-test are purely environmental mites, i.e. house dust mites and storage mites. A positive mite result in the pre-test therefore has nothing to do with ectoparasites!

In some cases, cross-reactions to Sarcoptes mites are possible, i.e. a dog with Sarcoptes infection can react positively to house dust mites.

Mites: How can you avoid house dust mites or storage mites?

Complete avoidance is usually not possible, but certain measures can be taken to reduce the incidence.

House dust mites are increasingly found in beds, upholstered furniture and carpets. Therefore, the dog should sleep in a carpet-free room (out of the bedroom and bed). If this is not possible, there are mite-proof covers for mattresses and dust mite-killing sprays (e.g. Milbiol®) in medical supply stores.

Storage mites are found in dry food, rice, flakes, etc., but also in house dust. This means that changing the food alone does not automatically reduce the storage mites to zero.

Mites in food: Does it help to freeze dry food so that the food mites are killed, or does their protein structure still remain as an allergen?

Mites that are present in the dry food die, but the allergen (the molecular structure) remains. i.e. if two mites were present, the allergen remains despite the death of these two mites, but further reproduction and thus increased allergen pressure are prevented. I.e. yes, freezing helps, but one should not be lulled into the false sense of security that this makes the food allergen-free (if many mites were already contained before, the allergen from these many mites also remains in the frozen food).

Feeding the atopic: Can fruits and vegetables also trigger contact or food allergies (cross-reactions to pollen)?

Yes, this is quite possible. Such phenomena are called cross-reactions (OAS = oral allergy syndrome); i.e. one does not only react to the already known allergen triggering the allergy, but can also show reactions to other substances with similar protein structures (epitopes). Similar molecular structures in environmental and food allergens cause the formation of cross-reacting IgE antibodies (pollen-associated food allergies = cross-reaction of allergens that occur both in pollen and in different foods/feedstuffs). These cross-reactions can occur, but do not necessarily have to. They can occur between fruits, fruits and pollen (“fresh fruit syndrome”); e.g. a birch pollen allergic person can react when eating carrots and/or apples. In human medicine, such reactions are well documented, but in veterinary medicine there are only a few publications on this.

The OAS due to fruit and vegetables should also be considered in elimination and provocation diets (see FAQ feed allergy).

Feeding the atopic: What is meant by "fresh fruit syndrome"?

This is a cross-reaction between birch pollen and fruits (especially apples) or vegetables (“fresh fruit syndrome”). This is also called oral allergy syndrome (OAS). The cause is a cross-reactivity between the allergy-causing protein structure of the pollen and the carbohydrate-protein shell of the food. Cooking and peeling can therefore be helpful.


FAQ = frequently asked questions

ASIT = Allergen-specific immunotherapy (new) = Hyposensitisation (old)

RK = reaction class