The aim of this article is to provide information to individuals who have or suspect an allergy to Anisakis simplex.
Anisakis simplex is a parasitic worm which infects marine fish or shellfish. The parasite can also infect humans (known as anisakiasis), as well as trigger allergic reactions in a very small minority of people.
Allergic reactions to Anisakis simplex can be mistaken for allergy to fish or shellfish. Anyone experiencing allergy-like symptoms to a particular fish or shellfish that they have previously eaten with no problem should consider the possibility that Anisakis simplex is responsible.
Although raw fish is the main risk factor for this allergy, a 2006 study found allergic symptoms in 8 patients previously diagnosed as being allergic to Anisakis simplex, after they ate rare chicken meat. Chicken feed can sometimes have a high proportion of fishmeal included, which could be contaminated by the Anisakis simplex parasite.
Symptoms of allergy can include hives (urticaria), swelling (angioedema), asthma or even a severe, life-threatening allergic reaction (anaphylaxis). There may also be abdominal pain, nausea and vomiting. Anaphylaxis should be treated as a medical emergency. Click here for further information on anaphylaxis and its treatment.
If you believe you may be allergic to Anisakis simplex the first thing you should do is visit your GP. A referral to an allergy clinic may be necessary.
If allergy tests are positive, we would advise you to avoid all ocean fish and shellfish. Based on expert advice, we believe you will be able to continue to eat freshwater fish, but we advise you to discuss this with your allergy specialist.
If your doctor or allergy specialist rules out allergy to Anisakis simplex, and to fish and shellfish, another possibility to consider is that your symptoms were caused by histamine poisoning. A chemical called histamine is sometimes present in spoiled fish (especially tuna and mackerel) and can cause symptoms similar to those of allergy. Anyone who ate the spoiled fish would be likely to be affected by histamine, although some people are more susceptible than others. Another term for this condition is scombroid poisoning.
The content of this fact sheet has been peer-reviewed by Dr Shuaib Nasser, Consultant in Allergy and Asthma at Cambridge University Hospitals NHS Foundation Trust. We are not aware of any conflicts of interest in relation to their review of this article.
All the information we produce is evidence based or follows expert opinion and is checked by our clinical and research reviewers. If you wish to know the sources we used in producing any of our information products, please let us know, and we will gladly supply details.
The information provided above is given in good faith. Every effort has been taken to
ensure accuracy. All patients are different, and specific cases need specific advice. There is no substitute for good medical advice provided by a medical professional.
Publication date: July 2021
Review date: July 2024