Differential symptoms of parasite infection by raw fish: Clonorchis sinensis (a trematode/fluke), Anisakis (a nematode/roundworm) and Diphyllobothrium a (cestode/tapeworm), all have gastrointestinal, but otherwise distinct, symptoms.
Clonorchiasis sinensis is a trematode (fluke) which is part of the phylum Platyhelminthes. It is a hermaphroditic fluke that requires two intermediate hosts. The parasitic worm is as long as 10 to 25mm and lives in the bile ducts of the liver. The eggs of the worms are passed through fecal matter which are then ingested by mollusks. One becomes infected by eating undercooked, smoked, pickled salted freshwater fish. Freshwater fish are a second intermediate host for the parasitic worm. They become infected when the larvae (cercaria) of the worm penetrates the flesh of the fish. The water snail is the first intermediate host in which a miracidium (an embryonated egg discharged in stool) goes through its developmental stages of (sporocyst, rediae and cercariae). Clonorchiasis is endemic in the Far East, especially in Korea, Japan, Taiwan, and Southern China. Clonorchiasis has been reported in non endemic areas (including the United States). In such cases, the infection follows the ingestion of imported, undercooked or pickled freshwater fish containing metacercariae.