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[Anisakis simplex] [Contracaeceum sp.] [Pseudoterranova decipiens]

L3 larva of Pseudoterranova sp. Ten units = one centimeter.

L3 larva of Pseudoterranova sp. Ten units = one centimeter.

Cross-section of <em>Pseudoterranova</em> sp. viewed under differential interference contrast (DIC) microscopy.

Cross-section of Pseudoterranova sp. viewed under differential interference contrast (DIC) microscopy.

Causal Agents

Anisakiasis is caused by the accidental ingestion of larvae of the nematodes (roundworms) Anisakis simplex and Pseudoterranova decipiens.

Life Cycle:

Life cycle of anisakiasis

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 Number 1. The eggs become embryonated in water, and first-stage larvae are formed in the eggs. The larvae molt, becoming second-stage larvae The Number 2a, and after the larvae hatch from the eggs, they become free-swimming The Number 2b. Larvae released from the eggs are ingested by crustaceans The Number 3. 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 The Number 4. Fish and squid maintain third-stage larvae that are infective to humans and marine mammals The Number 5.

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 The Number 7. 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).

Clinical Presentation

Within hours after ingestion of infected larvae, violent abdominal pain, nausea, and vomiting may occur. Occasionally the larvae are coughed up. If the larvae pass into the bowel, a severe eosinophilic granulomatous response may also occur 1 to 2 weeks following infection, causing symptoms mimicking Crohn's disease.

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  • Page last reviewed November 29, 2013
  • Page last updated November 29, 2013
  • Content source: Global Health - Division of Parasitic Diseases and Malaria
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