People who produce immunoglobulin E in response to this parasite may subsequently have an allergic reaction, including anaphylaxis, after eating fish infected with Anisakis species.

The infected crustaceans are subsequently eaten by fish or squid, and the nematodes burrow into the wall of the gut and encyst in a protective coat, usually on the outside of the visceral organs, but occasionally in the muscle or beneath the skin.

The life cycle is completed when an infected fish is eaten by a marine mammal, such as a whale, seal, sea lion, dolphin or another animal like a seabird or shark.

[citation needed] Anisakis share the common features of all nematodes: the vermiform body plan, round in cross section, and a lack of segmentation.

[6] Anisakiasis is a human parasitic infection of the gastrointestinal tract caused by the consumption of raw or undercooked seafood containing larvae of the nematode Anisakis simplex.

If the larvae pass into the bowel or large intestine, a severe eosinophilic granulomatous response may also occur one to two weeks following infection, causing symptoms mimicking Crohn's disease.

[14] The first case of human infection by a member of the family Anisakidae was reported in the Netherlands by Van Thiel, who described the presence of a marine nematode in a patient suffering from acute abdominal pain.

[citation needed] Important clues for the diagnosis of anisakiasis include a recent history of eating raw or insufficiently cooked fish or squid followed by the sudden start of epigastric or right lower quadrant stomach pain.

[17] Raising consumer and producer awareness about the existence of anisakid worms in fish is a critical and effective prevention strategy.

[citation needed] Many countries require all types of fish with potential risk intended for raw consumption to be previously frozen to kill parasites.

The frequency of allergic symptoms in connection with fish ingestion has led to the concept of gastroallergic anisakiasis, an acute IgE-mediated generalized reaction.

[26] Larval anisakids are common parasites of marine and anadromous fish (e.g. salmon, sardine), and can also be found in squid and cuttlefish.

In contrast, they are absent from fish in waters of low salinity, due to the physiological requirements of krill, which are involved in the completion of the worm's life cycle.

[28] Unusual hosts of Anisakis larvae in the Southern Hemisphere, rarely reported, include seabirds, sharks, or sea kraits.

There are three additional species classified as taxon inquirendum (A. dussumierii (Brenden, 1870), A. insignis (Diesing, 1851), and A. salaris (Gmelin, 1790) Yamaguti, 1935).