Liver Fluke Induces Cholangiocarcinoma
Figure 2
Life Cycles of O. viverrini and C. sinensis
Embryonated eggs are discharged in the biliary ducts and in the stool (1). Eggs are ingested by a suitable snail intermediate host (2); there are more than 100 species of snails that can serve as intermediate hosts. Each egg releases a miracidium (2a), which goes through several developmental stages (sporocyst [2b], redia [2c], and cercaria [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, such as Cyclocheilichthys armatus or Puntius leiacanthus, where it encysts as a metacercaria (3). Humans are infected through ingestion of undercooked, salted, pickled, or smoked freshwater fishes (4). After ingestion, the metacercaria excysts in the duodenum (5) and ascends the biliary tract through the ampulla of Vater. Maturation to adulthood (right, O. viverrini; left, C. sinensis) takes approximately one month (6). The adult flukes (measuring 10–25 mm by 3–5 mm) reside in the small and medium-sized biliary ducts. In addition to humans, carnivorous animals can serve as reservoir hosts. (Adapted from http://www.dpd.cdc.gov/DPDx/HTML/Opisthorchiasis.htm.)