The trematode Clonorchis sinensis (Chinese or oriental liver fluke) is an important foodborne pathogen and cause of liver disease in Asia. This appears to be the only species in the genus involved in human infection.
Clonorchis sinensis eggs are discharged in the biliary ducts and in the stool in an embryonated state . Eggs are ingested by a suitable snail intermediate host . Eggs release miracidia , which go through several developmental stages (sporocysts , rediae , and cercariae ). The cercariae are released from the snail and, after a short period of free-swimming time in water, they come in contact and penetrate the flesh of freshwater fish, where they encyst as metacercariae . Infection of humans occurs by ingestion of undercooked, salted, pickled, or smoked freshwater fish . After ingestion, the metacercariae excyst in the duodenum and ascend the biliary tract through the ampulla of Vater . Maturation takes approximately one month. The adult flukes (measuring 10 to 25 mm by 3 to 5 mm) reside in small and medium sized biliary ducts.
Life cycle image and information courtesy of DPDx.