Liver flukes life cycle

Embryonated eggs are discharged in the biliary ducts and in the stool (1). Eggs are ingested by a suitable snail intermediate host (2). Each egg releases a miracidia (2a), which go through several developmental stages (sporocysts (2b), rediae (2c), and cercariae (2d)). 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 (3). Infection of humans occurs by ingestion of undercooked, salted, pickled, or smoked freshwater fish (4). After ingestion, the metacercariae excyst in the duodenum (5) and ascend the biliary tract through the ampulla of Vater (6). 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. In addition to humans, carnivorous animals can serve as reservoir hosts.