Anisakis simplex




Rev 08/03/2020

  Classification Hosts
Morphology and Anatomy Life Cycle
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Rev. 08/03/2020



Class:    Chromadorea
SubClass: Spiruria
Order:       Ascaridida
Superfamily: Ascaridoidea
Family:         Anisakidae

                          Anisakis simplex Rudolphi, 1809 det Krabbe, 1878

Morphology and Anatomy:

whole anasakid Infective third-stage juvenile of Anisakis simplex
may reach a length of 2-4 cm.)



Economic Importance:

Anisakiasis has highest incidence in areas where raw fish is eaten (e.g., Japan, Pacific coast of South America, the Netherlands).


Marine mammals such as cetaceans (whales, dolphins) and pinnipeds (seals, sea lions, walruses) are the definitive (primary host for A. simplex; fish are an intermediate host.

Anisakiasis in humans is caused by the accidental ingestion of juveniles of A. simplex in raw or undercooked fish.


Intestinal mucosa

Life Cycle:

Life cycle of A. simplex or P. decipiens

Adults are embedded in clusters in the intestinal mucosa of marine mammals. Eggs are passed in the feces of the mammals  In the water, first-stage juveniles develop in the eggs and molt to the second-stage  . The juveniles hatch from the eggs in the second stage and are free-swimming in water  The juveniles are ingested by crustaceans  and develop to third-stage juveniles that are infective to fish and squid when they ingest crustaceans  In the fish or squid hosts, the juveniles migrate from the intestine to the tissues in the peritoneal cavity and grow up to 3 cm in length.  Upon the host's death, juveniles migrate to the muscle tissues and, through predation by other fish, are transferred to other fish hostsThird-stage juveniles persist in fish and squid maintain and are infective to marine mammals (and humans) when their hosts are consumed  .  When ingested by mammalian hosts, juveniles molt twice and 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 anisakid juveniles penetrate the gastric and intestinal mucosa, causing the symptoms of anisakiasis.

(adapted from



Anisakiasis in humans is expressed as violent abdominal pain, nausea, and vomiting within hours after ingesting Anisakis juveniles.  Occasionally the juveniles are coughed up; if they pass into the bowel, a severe eosinophilic granulomatous response may also occur 1 to 2 weeks following infection, with symptoms mimicking Crohn's disease.




Diagnosis is by gastroscopic examination  or by histopathologic examination of biopsy tissue.

Preferred treatment is surgical or endoscopic removal.  Drugs are available.

Prevention: adequate cooking of fish (60 C) or freezing (-20 C for seven days or -35 C for 15 hours) before ingestion will kill anisakid helminths.


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