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Tick bites can lead to meat allergy

The first case of meat allergy was described in Sweden in 2009, and it is now an established condition. Marianne van Hage, Professor of clinical immunology at Karolinska Institutet and senior physician at Karolinska University Hospital tells us more.

Marianne van Hage, credit: Erik Holmgren.What is meat allergy?
“It’s an allergy against the carbohydrate alfa-gal, which is found in red meat from any mammal. Patients may also have a reaction to dairy and gelatin, which also contain alfa-gal, but they can eat poultry, as this does not contain alfa-gal. The allergy is triggered by a tick bite, as the tick carries alpha-gal in the saliva and stomach. When you get bitten, the carbohydrate is transmitted through the skin, and some individuals then form IgE antibodies against alpha-gal. We ingest alpha-gal every time we eat meat, but then it enters the body via the gastrointestinal tract, where we instead produce IgG antibodies, which do not cause allergies.”

How common is it?
“It is not extremely common, but it is not completely uncommon either. Around 200 patients have received the diagnosis at Södersjukhuset in Stockholm, but we believe there is a large number of unreported cases. Nearly half have had the most serious form of allergic reaction, anaphylaxis. One problem is that the symptoms are delayed. The patient may have had meat in the evening and then woken up at night with severe symptoms. This makes it difficult, for both the patient and doctor, to link the allergic reaction to something that was ingested hours before. Alcohol, physical exertion and anti-inflammatory drugs also appear to aggravate the symptoms.”

How do you protect yourself?
“By wearing the right clothing in tick-infested areas. It appears as though people with blood type B or A/B are better protected, but not completely. The reason is that the antigen B blood type contains a carbohydrate similar to alpha-gal, which makes these people less prone to a reaction. Once you have a meat allergy, you simply have to avoid red meat and offal. There is no way to get rid of the alfa-gal through cooking, so if you eat meat, you will be exposed.

Text: Fredrik Hedlund, first published in Swedish in Medicinsk Vetenskap No 4/2018.