PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
Anisakiasis is caused by the accidental ingestion of larvae of the parasitic nematodes Anisakis simplex or Pseudoterranova decipiens. Anisakiasis usually occurs in the stomach and can then be diagnosed by endoscopy.
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- Adult stages of Anisakis simplex or Pseudoterranova decipiens live in the stomach of marine mammals. Eggs produced by adult females are passed in the faeces.
- First-stage larvae are formed when in the water. The larvae moult to become second-stage larvae, which then hatch from the eggs and become free-swimming.
- The larvae released from the eggs are ingested by crustaceans and then develop into third-stage larvae. The crustaceans are eaten by fish and squid, where the larvae migrate from the intestine to the peritoneal cavity and grow up to 3 cm in length.
- When the host dies, larvae migrate to the muscle tissues and are transferred from the fish to the predator.
- When fish or squid containing third-stage larvae are ingested by marine mammals, the larvae develop into adult worms. The adult females produce eggs that are shed by marine mammals.
- Humans become infected by eating raw or undercooked infected marine fish. After ingestion, the larvae penetrate the stomach (less often the intestine), causing the symptoms of anisakiasis.
- Distribution is worldwide but there is a higher incidence in areas where raw fish is eaten - for example, Japan, the Pacific coast of South America, and the Netherlands.
- With the increasing worldwide popularity of Japanese cuisine, the traditional Japanese fish dishes sushi and sashimi, which are served in Japanese restaurants and sushi bars, have been suspected of causing fishborne parasitic infestations, especially anisakiasis.
- Within hours after ingestion of infected larvae, violent abdominal pain, nausea, and vomiting may occur.
- Anisakiasis affecting the small bowel is very rare but may present with abdominal pain and even small bowel obstruction, intussusception, perforation, peritonitis, or intestinal bleeding.
- Larvae in the bowel can also cause a severe eosinophilic granulomatous response 1 to 2 weeks after infection, causing symptoms resembling Crohn's disease.
- Anisakiasis may cause acute hypersensitivity and chronic urticaria.
- Patients sensitised by prior consumption of parasitised fish develop, within a few hours, violent abdominal pain and an allergic reaction. Anisakis-induced urticaria is seen in about one in five cases.
- Ingestion of dead worms in fish can cause severe hypersensitivity reactions. Even anaphylactic reactions may occur following exposure to allergens from dead worms by foodborne, airborne or skin contact routes.
Diagnosis can be made by:
- Gastroscopy: 2 cm larvae are seen and can be removed.
- Histology of biopsy tissue removed at endoscopy or during surgery.
- Enteric anisakiasis is difficult to diagnose and diagnosis is usually based on an accurate history of eating raw fish before the onset of symptoms.
The treatment of choice is surgical or endoscopic removal.
Further reading & references
- Parasites A-Z; Centers for Disease Control and Prevention
- Hökelek M et al; Nematode Infections, Medscape, Dec 2011
- Anisakiasis, DPDx, Centers for Disease Control & Prevention
- Nawa Y, Hatz C, Blum J; Sushi delights and parasites: the risk of fishborne and foodborne parasitic Clin Infect Dis. 2005 Nov 1;41(9):1297-303. Epub 2005 Sep 22.
- Kang DB, Oh JT, Park WC, et al; (Small bowel obstruction caused by acute invasive enteric anisakiasis.) Korean J Gastroenterol. 2010 Sep;56(3):192-5.
- Yasunaga H, Horiguchi H, Kuwabara K, et al; Clinical features of bowel anisakiasis in Japan. Am J Trop Med Hyg. 2010 Jul;83(1):104-5.
- Daschner A, Pascual CY; Anisakis simplex: sensitization and clinical allergy. Curr Opin Allergy Clin Immunol. 2005 Jun;5(3):281-5.
- Petithory JC; (New data on anisakiasis) Bull Acad Natl Med. 2007 Jan;191(1):53-65; discussion 65-6.
- Audicana MT, Kennedy MW; Anisakis simplex: from obscure infectious worm to inducer of immune Clin Microbiol Rev. 2008 Apr;21(2):360-79, table of contents.
- Rodriguez-Mahillo AI, Gonzalez-Munoz M, de las Heras C, et al; Quantification of Anisakis simplex allergens in fresh, long-term frozen, and Foodborne Pathog Dis. 2010 Aug;7(8):967-73.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Colin Tidy
Dr Colin Tidy