A 48-year-old Chinese immigrant with long-standing right hypochondrial discomfort develops progressive jaundice and weight loss. Ultrasound shows dilatation of intrahepatic bile ducts, and MRCP reveals filling defects within them. He habitually eats undercooked freshwater fish. Cholangiography confirms a fluke in the biliary tree. What is the infective stage transmitted to humans?
- A Fork-tailed cercaria penetrating intact skin
- B Embryonated egg ingested in contaminated vegetables
- C Encysted larva in crab muscle
- D Metacercaria encysted in fish flesh ✓
Correct answer: D. Metacercaria encysted in fish flesh
Explanation
Clonorchis sinensis, the Chinese liver fluke, is acquired by eating raw or undercooked freshwater fish containing metacercariae, which excyst in the duodenum and ascend the biliary tract. Chronic infection causes adenomatous hyperplasia of bile duct epithelium and predisposes to cholangiocarcinoma. Fork-tailed cercariae penetrate skin in schistosomiasis, and crab-borne larvae belong to Paragonimus, making those options wrong for this route.
Reference: Paniker's Textbook of Medical Parasitology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.