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For further information, see CMDT Part 35-31: Anisakiasis

Key Features

Essentials of Diagnosis

  • Nausea, vomiting, and progressive epigastric pain

  • Occasionally, acute infection is followed by a chronic course

  • Infection is by larval invasion of the stomach or intestinal wall by anisakid nematodes

General Considerations

  • Caused by infection with larvae of parasites of saltwater fish and squid

  • Multiple species of the family Anisakidae may occasionally infect humans

  • Definitive hosts for these parasites are marine mammals

  • Eggs are passed in the feces and ingested by crustaceans, which are then eaten by fish and squid

  • When ingested by humans in undercooked seafood, larvae penetrate the stomach or intestinal wall but cannot complete their life cycle


  • Most common in Japan

Clinical Findings

Symptoms and Signs

  • Clinical manifestations follow burrowing of worms into the stomach or intestinal wall, leading to

    • Localized ulceration

    • Edema

    • Eosinophilic granuloma formation

  • Acute infection

    • Causes severe epigastric or abdominal pain, nausea, and vomiting (usually within 2 days of parasite ingestion)

    • May cause allergic symptoms (eg, urticaria, angioedema, and anaphylaxis)

    • Generally resolves within 2 weeks

  • Chronic symptoms suggest

    • Inflammatory bowel disease

    • Diverticulitis

    • Carcinoma

  • Rarely, worms may migrate to other sites or be coughed up

Differential Diagnosis

  • Norwalk virus or rotavirus

  • "Food poisoning" by toxins from Bacillus cereus, Staphylococcus aureus, Clostridium perfringens

  • Appendicitis

  • Peptic ulcer disease or gastritis

  • Inflammatory bowel disease


Laboratory Tests

  • Eosinophilia is not usually seen

Imaging Studies

  • Radiographs may identify stomach or intestinal lesions

Diagnostic Procedures

  • Diagnosis is suggested in persons with acute abdominal symptoms after eating raw fish

  • Endoscopy may allow visualization and removal of the worm



  • Specific therapy is not indicated


  • When surgery is performed due to consideration of other diagnoses, eosinophilic inflammatory lesions and invading worms are found

Therapeutic Procedures

  • Endoscopic worm removal hastens recovery

  • Parasites are killed by cooking or deep freezing fish



  • Chronic intestinal anisakiasis

When to Refer

  • Refer for consideration of mechanical removal of the worm


  • Avoidance of ingestion of raw or incompletely cooked squid or marine fish, especially salmon, rockfish, herring, and mackerel; early evisceration of fish is recommended

  • Larvae within fish may, with difficulty, be seen as colorless, tightly coiled or spiraled ...

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