Anisakis is a nematode (roundworm) known to cause a parasitic disease called anisakiasis. In anisakiasis the stomach or intestine wall of humans get invaded by the parasite. The transmission of this disease occurs when infective larvae are ingested from fish or squid that humans eat raw or undercooked. Symptoms of anisakiasis include abdominal pain, nausea, vomiting, and diarrhea. In severe cases, the worm can cause peritonitis (inflammation of the lining of the abdomen) or intestinal obstruction.
Anisakiasis is most common in Japan, where infected fish are usually eaten raw. However, the condition is becoming more common in other parts of the world as sushi and sashimi become more popular.