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).

Figure 2 Adult worm of human liver flukes: a: O viverrini; b: O felineus; c: C sinensis. The average size of O viverrini worm is 7.0 (5.4-10.2) x 1.5 (0.8-1.9) mm[8]. (Adapted from Ash, 1997).

Figure 3 Preparation of koi pla, pla som, pla ra and jaewbhong. koi pla is prepared with the fish-based meals with local herbs, spices, condiments, rice, and vegetables. Pla som is moderately fermented or stored for a few days to weeks.Pla ra is fermented fish sauce, popular in Northeastern Thai cuisine. It is made by combining fish, salt, and roasted rice, fermenting in a pot for one to three months. jaewbhong is made by combining pla ra and chili.

Figure 4 Prevalence of O viverrini infection in Thailand[15], OV: Percentage of O viverrini infection.

Figure 5 Proposed mechanisms of Opisthorchis-derived CCA initiation. (Adapted from Sripa et al[30]).