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.
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. Follow the links near the bottom of this page for 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.
Detailed information on anaphylaxis and its treatment can be found here:
References — All the information we produce is evidence based or follows expert opinion and is checked by our expert 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.
Reviewers — The content of this knowledgebase has been peer-reviewed by Dr Shuaib Nasser, Consultant in Allergy and Asthma at Cambridge University Hospitals NHS Foundation Trust; and Dr Isabel Skypala, Consultant Allergy Dietitian, Royal Brompton & Harefield NHS Foundation Trust and Honorary Senior Clinical Lecturer – Imperial College, London. We are not aware of any relevant conflicts of interest on respect of these reviewers.
Disclaimer — 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.
Date created: May 2018
Next review date: May 2021