Page 149 - Medical Parasitology_ A Textbook ( PDFDrive )

142 12 Trematodes: Flukes

Liver Flukes

Clonorchis sinensis

Common name The Chinese liver fluke, oriental liver fluke

Distribution
Human clonorchiasis occurs in Japan, Korea, Taiwan, China and Vietnam.

Habitat
Adult worm lives in the biliary tract.

Morphology
The adult worm has a flat, transparent, spatulate body; pointed anteriorly and
rounded posteriorly (Fig. 12.5a). It is 10–25 mm long and 3–5 mm broad. The adult
worm can survive many years in the biliary tract. The worm is hermaphrodite and
passes eggs into the bile duct. The testes of the adult worm are branched.
Its eggs are broadly ovoid, 30 μm by 15 μm with a yellowish brown (bile-stained)
shell. It is jug shaped and operculated with characteristic shoulders (Fig. 12.5b). At
the terminal end of the egg, a small knob is sometimes visible. The eggs passed in
faeces contain ciliated miracidia.

Life Cycle (Fig. 12.6)
(1) Embryonated eggs are passed out in faeces of infected human. (2) The eggs in
water are ingested by freshwater snail. (3) Free swimming cercariae released by the
snail encyst in the skin or flesh of freshwater fish. (4) The metacercariae in flesh or
skin of freshwater fish are ingested by human host. (5–6) The metacercariae excyst
in the duodenum and adults develop in the biliary duct.

a b

Fig. 12.5 Clonorchis sinensis. (a) Adult, (b) Egg