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Symptoms triggered by eating fish - an unexpected cause

March 2012: Researchers have reported the case of a 61-year-old woman who suffered a severe allergic reaction after eating raw mackerel. When allergy tests to mackerel proved negative, there was uncertainty about what had actually caused the reaction. However, further testing revealed that the woman was allergic to anisakis simplex, a worm-like parasite that lives in some fish and shellfish.


The conclusion from this case is that the causes of allergic reactions may seem obvious, but sometimes there is another, less obvious trigger. Anyone reacting to a particular fish that they have previously eaten with no problem should consider the possibility that the parasite anisakis simplex was responsible and seek medical advice.


The above research took place in Japan and allergy to anisakis simplex (also known as the cod worm) has also been well-documented in other parts of the world. The 61-year-old woman at the centre of the study recovered with an injection of adrenaline and diagnosis of allergy to anisakis simplex was confirmed by blood tests. The researchers concluded that patients suspected to have fish allergy or idiopathic allergy (where the cause is unknown) should be examined for evidence of anisakis-induced allergy.


Their work is published in the Journal of Infection & Chemotherapy.

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It’s important to note that anisakis simplex can also cause human infection if it is not destroyed during cooking. Allergic reactions are rarer, but should not be overlooked as a cause of symptoms. The allergens are quite thermostable and neither cooking nor freezing can prevent allergic reactions in sensitised patients.


Another condition sometimes mistaken for fish allergy is histamine poisoning (also called scombroid poisoning). The reason for the confusion is that ingestion of histamine, which is sometimes present in spoiled fish such as tuna or mackerel, can cause symptoms similar to those of allergy. Unlike an allergy, this would affect everyone who consumed the offending food, although some are more susceptible than others.


Symptoms can include nausea, vomiting, diarrhea, an oral burning sensation or peppery taste, hives, itching, red rash, and even a fall in blood pressure typical of a severe allergic reaction. 


Foods containing unusually high levels of histamine may not necessarily appear to be outwardly spoiled. Histamine formation in fish can be prevented by proper handling and refrigerated storage.


On rare occasions, certain cheeses can also cause histamine poisoning. The control of histamine formation seems dependent on insuring that histamine-producing bacteria are not present in significant numbers in the raw milk.


To read the abstract of the research reported above, click here.


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