Opisthorchis viverrini: The carcinogenic human liver fluke

Figure 1 Life cycle of O viverrini. 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), sporocysts (2b), rediae (2c), and cercariae (2d). The cercaria is released from the snail and after a short period of free-swimming time in water, it penetrates the flesh of a freshwater fish, where it encysts as a metacercaria (3). Humans are infected through ingestion of undercooked or raw freshwater fishes (4). The metacercaria excysts in the duodenum (5) and ascends the biliary tract through the ampulla of Vater. Maturation to adulthood takes approximately one month (6). (Adapted from: http://www.dpd.cdc.gov/DPDx/HTML/Opisthorchiasis.htm).