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Causal Agent:

Trematodes (flukes) Opisthorchis viverrini (Southeast Asian liver fluke) and O. felineus (cat liver fluke).

Life Cycle:

Opisthorchis viverrini lifecycle

The adult flukes deposit fully developed eggs that are passed in the feces The number 1. After ingestion by a suitable snail (first intermediate host) The number 2, the eggs release miracidia The number 2a, which undergo in the snail several developmental stages (sporocysts The number 2b, rediae The number 2c, cercariae The number 2d). Cercariae are released from the snail The number 3 and penetrate freshwater fish (second intermediate host), encysting as metacercariae in the muscles or under the scales The number 4. The mammalian definitive host (cats, dogs, and various fish-eating mammals including humans) become infected by ingesting undercooked fish containing metacercariae. After ingestion, the metacercariae excyst in the duodenum The number 5 and ascend through the ampulla of Vater into the biliary ducts, where they attach and develop into adults, which lay eggs after 3 to 4 weeks The number 6. The adult flukes (O. viverrini: 5 mm to 10 mm by 1 mm to 2 mm; O. felineus: 7 mm to 12 mm by 2 mm to 3 mm) reside in the biliary and pancreatic ducts of the mammalian host, where they attach to the mucosa.

Life cycle image and information courtesy of DPDx.