[4][5] This species begins as an egg found in the feces of its host, and hatches as a second-stage larva in the ocean, where it survives for several days.

[6] The consumption of raw or undercooked seafood, such as sashimi and ceviche, puts humans at risk for developing an infection or allergic reaction caused by A.

[3][5] The worm can infect the stomach or intestine by lodging itself within the walls of the organ and producing digestive enzymes to penetrate mucus layers.

[2][5] It possesses the typical characteristics of its phylum, including an unsegmented, cylindrical body that occasionally fills up with fluids and allows it to swim freely.

[2] A. simplex is also part of the Anisakidae family and the Anisakis genus, which are specifically known for their potential to spread diseases from one species to another, starting with the infection of animals, such as fish, and eventually leading to transmission in humans.

[3] In its early stages, the larva can be found in the faeces of its host, and is around 5mm in length, presenting a boring tooth and a bundle of sensory nerves at the front tip of its body.

[5][4] Once it develops into a third stage larva, it grows to a length of 20 to 30 mm, and is found in the body cavity of the host, either freely floating or enclosed in a protective sac attached to the main organs.

[6] At the rear end, the mucron is replaced by a cone-shaped protrusion with small globular structures on it, and the previously irregular striations and indents on the outer surface of the organism become regularly patterned.

[6] At this stage, female larvae begin to develop reproductive organs at the center of their bodies, including internal genitalia, uteri and surrounding papillae.

The egg of the A. simplex is first found in the fecal matter of its final host in an unembryonated form, and is visibly transparent and circular, with an evenly-surfaced shell.

[4] However, the release of eggs from the final host is unaffected by seasonal factors or temperatures, so the rate of infection by the species is stable throughout the year.

[5] The krill infected by third stage larvae are then ingested by common predators, such as squid and fish, specifically teleosts, who then become paratenic hosts.

[5] At this stage, the larvae no longer roam freely in the gut of the host, but are rather embedded in their viscera, specifically in the mucus layers of the stomach, and eventually make their way into the inner muscles.

[7] Certain species of paratenic hosts are sold and consumed by humans, including salmon, mackerel, cod, anchovy, sardine and squids.

[7] The consumption or management of raw seafood puts humans at risk for developing an infection or allergic reaction caused by Anisakis simplex.

[7] Anisakiasis occurs when a parasitic worm, such as A. simplex, latches onto and penetrates the stomach or intestinal lining of a human, causing an infection.

[3] Acute symptoms, such as abdominal cramps, nausea, fever, diarrhoea, and bloating begin to appear within a few hours of ingestion and signals the onset of gastric anisakiasis.

[7] Occasionally, people can sense the tingling of the worm in their oesophagus directly after ingestion, and can vomit to expel it from their body and prevent infection.

[7] However, if the worm reaches the stomach, it uses its protruding lip segments to penetrate the gastric mucosa, and releases tissue-dissolving enzymes to eventually make its way into the submucosa.

[3][8] A typical endoscopy of the acute gastric form shows a worm embedded within the submucosa, with a visible lesion at the site of entry, and a thicker oedematous stomach lining.

[3] An allergy to A. simplex is diagnosed on the basis of three outcomes: a history of allergic reactions to seafood, the confirmation of relevant antibodies in an in vivo or in vitro test,  and the absent role of fish proteins.

For example, the frequent consumption of ceviche in South America, smoked herring in the Netherlands, and pickled anchovies in Spain poses a high risk of infection in these regions.