Anisakis Raw Fish Parasite

Scared of sushi? The Anisakis worm is a parasite that can cause nasty infections in humans who enjoy eating raw fish. It is 2 cm long and is sometimes coughed up after ingesting it in raw or undercooked fish.

Species Name: Anisakis simplex

Type of Microbe: Parasitic nematode (roundworm)

Japanese seafood sushi, roll and chopstick on white plate
SilviaMilanova / Getty Images

How It Spreads

Anisakis simplex has a complex life cycle in which humans are an incidental host. Adult worms are found in the stomach of marine mammals, and their eggs are passed in the feces. After the larvae are hatched, they are ingested by shellfish. Infected shellfish get eaten by fish and squid, where the larvae make their way into the muscle tissues. Ingestion of infected fish or squid by other fish allows the spread of the infection. Ingestion by marine mammals is necessary for the larvae to develop into adult worms. However, accidental human consumption of raw or undercooked marine fish that harbor the infected larvae can result in an allergic reaction, sometimes causing the individual to cough up the worms if swallowed. Penetration of the worms into the intestinal tissue causes anisakiasis.

You're at risk if you eat raw or undercooked seafood. The parasite is found frequently in cod, haddock, fluke, Pacific salmon, herring, flounder, and monkfish.

The US reports fewer than 10 diagnosed cases each year. In Japan, where raw fish is an integral part of the Japanese diet, more than 1000 cases have been reported each year.

Symptoms and Diagnosis

Penetration of the worm into intestinal tissues causes a local inflammatory immune response that results in the symptoms of anisakiasis. Common symptoms include:

After penetrating the intestine, the worm attracts white blood cells called eosinophils and macrophages and forms a mass of immune tissues called a granuloma.

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

Human infection is a dead end in the parasite’s life cycle. The worms are usually eliminated or expelled from the intestines within 3 weeks of infection.

Treatment and Prevention

Treatment is surgical or endoscopic removal of the parasites.

The FDA has provided several guidelines for retailers who sell fish intended to be eaten raw. These guidelines include freezing the fish to -31°F for 15 hours or -4°F for 7 days to kill parasites and physical examination known as “candling” for the presence of worms.


If the worm is not coughed up or vomited out, it may penetrate the intestinal tissues, causing a severe immune response that resembles appendicitis or Crohn’s disease.

Frequently Asked Questions

  • What are the symptoms of anisakiasis?

    Symptoms of anisakiasis can include violent abdominal pain, nausea, and vomiting. When the Anisakis worm enters intestinal tissues, it triggers an inflammatory immune response in the body, resulting in these symptoms.

  • Which types of fish carry the Anisakis worm?

    Larvae of the Anisakis worm can be carried by raw or undercooked marine fish and squid. Some examples include cod, flounder, fluke, haddock, herring, monkfish, and Pacific salmon.

  • Does freezing fish kill its parasites?

    Yes, freezing fish for certain lengths of time should kill its parasites. The Food and Drug Administration (FDA) provides guidelines on how to eliminate parasites for retailers who sell raw fish.

  • How is anisakiasis treated?

    Anisakiasis is treated by removing the parasite through either endoscopy or surgery. This may be necessary if the Anisakis worm is not naturally expelled from the body and causes intestinal issues.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. European Academy of Allergy and Clinical Immunology. Anisakis.

  2. Centers for Disease Control and Prevention. Anisakiasis.

  3. Centers for Disease Control and Prevention. Anisakiasis FAQs.

By Ingrid Koo, PhD
 Ingrid Koo, PhD, is a medical and science writer who specializes in clinical trial reporting