Anisakiasis FAQs

What is anisakiasis?

Anisakiasis, or herring worm disease, is a parasitic disease caused by nematodes (worms) that attach to the wall of the esophagus, stomach, or intestine. The best ways to prevent this disease is to avoid eating raw or undercooked fish or squid.

How does one become infected?

When certain infected marine mammals (such as whales or sea lions) defecate into the sea, eggs are released and become infective larvae while in the water. These larvae are ingested by crustaceans, which are then eaten by fish or squid. When humans eat raw or undercooked infected fish or squid, they ingest nematode larvae. Once inside the human body, the larvae can invade the gastrointestinal tract. Eventually, the parasite dies and produces an inflamed mass in the esophagus, stomach, or intestine.

Some people experience a tingling sensation after or while eating raw or undercooked fish or squid. This is actually the worm moving in the mouth or throat. These people can often extract the worm manually from their mouth or cough up the worm and prevent infection. Also, some people experience vomiting as a symptom and this can often expel the worm from the body.

Where is anisakiasis found?

Anisakiasis is most commonly found in areas where eating raw fish is popular, such as Japan. However, since eating undercooked fish is becoming more common, there have been cases seen in the United States, Europe, South America, and other areas of the world. Anyone who eats undercooked or raw fish or squid is at risk.

How is it diagnosed?

A history of eating undercooked fish or squid is helpful. Diagnosis is generally made by endoscopy, radiography, or surgery if the worm has embedded.

Can anisakiasis be transmitted human to human?

No. Anisakiasis cannot be transmitted human to human.

What are the signs and symptoms?

The signs and symptoms of anisakiasis are abdominal pain, nausea, vomiting, abdominal distention, diarrhea, blood and mucus in stool, and mild fever. Allergic reactions with rash and itching, and infrequently, anaphylaxis, can also occur.