Atlas of foodborne infections
transmitted by contaminated food and water

Atlas of Patogens Contents Information sources Glossary Administration

Anisakis simplex

CZ: anisakis
EN: herring worm

Occurrence:
Fish and Fish Products


Category:
Parasites


Foodborne Disease:
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anisakiosis - individual feels a tingling or tickling sensation in the throat and coughs up or manually extracts a nematode; in severe cases - abdominal pain (like acute appendicitis) and nausea.


Description:
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Anisakis simplex (herring worm) in human causes infection anisakiasis, which is most frequently diagnosed when the affected individual feels a tingling or tickling sensation in the throat and coughs up or manually extracts a nematode. In more severe cases there is acute abdominal pain, much like acute appendicitis accompanied by a nauseous feeling.

Symptoms occur from as little as an hour to about 2 weeks after consumption of raw or undercooked seafood. One nematode is the usual number recovered from a patient. With their anterior ends, these larval nematodes from fish or shellfish usually burrow into the wall of the digestive tract to the level of the muscularis mucosae (occasionally they penetrate the intestinal wall completely and are found in the body cavity).

They produce a substance that attracts eosinophils and other host white blood cells to the area. Anisakids rarely reach full maturity in humans and usually are eliminated spontaneously from the digestive tract lumen within 3 weeks of infection. Severe cases of anisakiasis are extremely painful and require surgical intervention.

Seafood is the principal source of human infections with these larval worms. The adults of A.simplex are found in the stomachs of whales and dolphins. Fertilized eggs from the female parasite pass out of the host with the host's faeces. In seawater, the eggs embryonate, developing into larvae that hatch in seawater.

These larvae are infective to copepods (minute crustaceans related to shrimp) and other small invertebrates. The larvae grow in the invertebrate and become infective for the next host, a fish or larger invertebrate host such as a squid.

These parasites are known to occur frequently in the flesh of cod, haddock, fluke, pacific salmon, herring, flounder, and monkfish. The disease is transmitted by raw, undercooked or insufficiently frozen fish and shellfish, and its incidence is expected to increase with the increasing popularity of sushi and sashimi bars. This disease is known primarily from individual cases.

Japan has the greatest number of reported cases because of the large volume of raw fish consumed there.


Pictures:

Anisakis simplex
Source: adult worm
Anisakis simplex
Source: adult worm
Anisakis simplex
Source: infected crustaceans are eaten by fresh squids or fish
Anisakis simplex
Source: Life cycle of genus Anisakis
Anisakis simplex
Source: marine mammals like a final hosts
Anisakis simplex
Source: overview of crustanceans

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