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Causal Agents:
Anisakiasis is caused by the
accidental ingestion of larvae of the nematodes (roundworms) Anisakis simplex and
Pseudoterranova decipiens.
Life Cycle:
Adult stages of
Anisakis simplex or Pseudoterranova decipiens reside
in the stomach of marine mammals, where they are embedded in the mucosa, in clusters.
Unembryonated eggs produced by adult
females are passed in the feces of marine mammals
.
The eggs become embryonated in water, and first-stage larvae are formed in the eggs.
The larvae molt, becoming second-stage larvae
,
and after the larvae hatch from the
eggs, they become free-swimming
.
Larvae released from the eggs
are ingested by crustaceans
.
The ingested larvae develop into third-stage larvae that are infective to fish and
squid
.
The larvae migrate from the intestine to the tissues in the peritoneal cavity and grow up to 3 cm in length.
Upon the host's
death, larvae migrate to the muscle tissues, and through predation, the larvae are transferred from fish to fish.
Fish and
squid maintain third-stage larvae that are infective to humans and marine
mammals
.
When fish or squid containing third-stage larvae are ingested by marine
mammals, the larvae 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 larvae penetrate the gastric and intestinal mucosa, causing the symptoms of anisakiasis.
Geographic
Distribution:
Worldwide, with
higher incidence in areas where raw fish is eaten (e.g., Japan, Pacific
coast of South America, the Netherlands).
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