Clonorchiasis — DTM&H MCQ

Correct answer: B — Clonorchis sinensis infection

Clonorchis sinensis infection (option B) is correct because the vignette combines the two classic discriminators for this fluke: decades of raw freshwater fish consumption in an East Asian patient and small operculated eggs on stool microscopy. Clonorchis sinensis, the Chinese liver fluke, is acquired by eating raw or undercooked freshwater fish containing metacercariae, and adult flukes then live in the intrahepatic and common bile ducts. Chronic biliary infestation causes recurrent pyogenic cholangitis, periductal fibrosis and is an established risk factor for cholangiocarcinoma, exactly matching this patient's history. The small, operculated, bile-stained egg with a shouldered operculum and abopercular knob is the classic stool finding for Clonorchis (and the near-identical Opisthorchis), distinguishing it from the other trematode and cestode eggs listed. Why the other options are wrong: E. Fasciola hepatica infection: acquired from watercress or other aquatic vegetation, not raw fish, and produces large unembryonated eggs without cholangiocarcinoma association; it typically causes acute hepatic/biliary migration symptoms rather than chronic biliary carcinogenesis. A. Paragonimus westermani infection: acquired from raw freshwater crab or crayfish, primarily causes pulmonary disease with brownish operculated eggs coughed up in sputum, not passed predominantly in stool, and has no cholangiocarcinoma link. D. Schistosoma japonicum infection: transmitted by cercariae penetrating skin from freshwater contact, not by eating fish, and produces large lateral-spined eggs, with hepatosplenic fibrosis rather than biliary tree cancer risk. C. Diphyllobothrium infection: a cestode (tapeworm) from raw freshwater fish that causes vitamin B12 deficiency, producing large operculated eggs without an abopercular knob, and has no association with cholangiocarcinoma. Key point: raw freshwater fish plus small operculated eggs plus chronic cholangitis with cholangiocarcinoma risk points specifically to Clonorchis sinensis, not the other trematodes or cestode acquired by different routes.

Reference: CDC DPDx, Clinical Overview of Clonorchis, Liver Flukes (parasitology reference used in UK DTMH and tropical medicine teaching), https://www.cdc.gov/liver-flukes/hcp/clinical-overview-clonorchis/index.html