The trematode Clonorchis sinensis (Chinese or oriental liver fluke).
Embryonated eggs are discharged in the biliary ducts and in the stool
. Eggs are ingested by a suitable snail intermediate host
. Each egg releases a miracidia
, which go through several developmental stages (sporocysts
, 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 1 month. The adult flukes (measuring 10 to 25 mm by 3 to 5 mm) reside in small and medium sized biliary ducts. In addition to humans, carnivorous animals can serve as reservoir hosts.
Life cycle image and information courtesy of DPDx.