Anisakiasis, also known as herring worm disease, is caused by consuming raw or undercooked fish infected with nematodes. The life cycle of the worm begins in marine mammals, and larvae can infect humans and cause abdominal pain, nausea, and vomiting. The disease is treated by surgically removing the worm, and can be prevented by cooking seafood to a high temperature or freezing it for seven days.
Anisakiasis is a parasitic disease caused by the consumption of raw or undercooked fish; it is also known as herring worm disease. Infected fish contain larvae of the nematodes Anisakis simplex or Pseudoterranova decipiens. The life cycle of worms passes through mammalian hosts, fish and crustaceans 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 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, within which the larvae further mature. The crustaceans are then eaten by fish and squid and the larvae migrate into the meat of fish and squid.
At this stage, the larvae in fish and squid are infective to humans and marine mammals. If a human eats fish or squid at this point, he or she can become infected and develop anisakiasis. A doctor can diagnose the disease by gastroscopic examination, in which he can see and remove the larvae in the stomach.
Some people report feeling an itchy sensation while eating infected fish. This sensation is produced by the larvae moving around in the mouth or throat. In these cases, the person may often pick the larvae out of their mouth or expel the swallowed larvae. Vomiting can also expel the parasite.
Once ingested, the larvae invade the gastrointestinal wall, causing abdominal pain, nausea, diarrhea, abdominal distension, 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 patients who do not recall any symptoms may have been unaware of the short-term symptoms caused by this process. Anisakiasis is treated by surgically removing the adult worm from the body.
The disease was first recognized in the Netherlands in 1960, but is found wherever 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 geographic 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 get the disease is to eat raw or undercooked 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 the fish or squid for seven days at -4° Fahrenheit (about -20° Celsius) will also kill the parasite.
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