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What is Anisakiasis?

By Jillian O Keeffe
Updated Mar 03, 2024
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Anisakiasis is a parasitic disease caused by eating raw or undercooked fish; it is also known as herring worm disease. The infected fish contains larvae of the roundworms Anisakis simplex or Pseudoterranova decipiens. The lifecycle of the worms goes through mammal, fish and crustacean hosts before infecting human gastrointestinal tracts and causing disease.

The life cycle of the worm begins in an infected marine mammal such as a whale or sea lion. When the mammal defecates in the water, it releases worm eggs. The eggs in the water develop into embryos and then into larvae. The larvae hatch in the water and are eaten by crustaceans, inside which the larvae mature further. The crustaceans are then eaten by fish and squid and the larvae migrate into the fish and squid flesh.

At this stage, the larvae in the fish and squid are infectious to humans and marine mammals. If a human happens to eat the fish or the squid at this point, he can become infected and develop anisakiasis. A doctor can diagnose the disease by gastroscopic examination, by which he can see and remove the larvae in the stomach.

Some people say they can feel an itching sensation as they are eating infected fish. This sensation is produced by the larvae moving in the mouth or in the throat. In these cases, the person can often take the larvae from his mouth or cough up the ingested larvae. Vomiting can also expel the parasite.

Once ingested, the larvae invade the gastrointestinal wall, causing abdominal pain, nausea, diarrhea, abdominal distention, blood and mucus in the stool, vomiting and fever, although some infected people show no symptoms. Dead worms cause inflammation in the gastrointestinal tract. The larvae penetrate the gastrointestinal wall within 10 minutes of ingestion, so the patients who remember no symptoms may have disregarded the short-term symptoms caused by this process. Anisakiasis is cured by surgical removal of the full-grown worm from the body.

The disease was first recognized in the Netherlands in 1960 but is found anywhere people eat raw or undercooked fish. For example, the disease is particularly common in Japan and along the west coast of South America. Cases in the United States, Europe and other geographical areas are most often associated with the consumption of sushi and sashimi.

Anisakiasis cannot be transmitted from human to human, so the only way to contract the disease is by eating undercooked or raw fish. The U.S. Centers for Disease Control and Prevention (CDC) recommend cooking seafood to reach an internal temperature of at least 145° Fahrenheit (about 63° Celsius). Freezing fish or squid for seven days at -4° Fahrenheit (about -20° Celsius), will also kill the parasite.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
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