Clonorchiasis

Causal Agent: The trematode Clonorchis sinensis (Chinese or oriental liver fluke).

Life Cycle:

Embryonated eggs are discharged in the biliary ducts and in the stool . Eggs are ingested by a suitable snail intermediate host . Each egg releases a miracidia , which go through several developmental stages (sporocysts , rediae , and cercariae ). The cercariae are released from the snail and after a short period of free-swimming time in water, they come in contact and penetrate the flesh of freshwater fish, where they encyst as metacercariae . Infection of humans occurs by ingestion of undercooked, salted, pickled, or smoked freshwater fish . After ingestion, the metacercariae excyst in the duodenum and ascend the biliary tract through the ampulla of Vater . Maturation takes approximately 1 month. The adult flukes (measuring 10 to 25 mm by 3 to 5 mm) reside in small and medium sized biliary ducts. In addition to humans, carnivorous animals can serve as reservoir hosts.

Geographic Distribution: Endemic areas are in Asia including Korea, China, Taiwan, and Vietnam. Clonorchiasis has

been reported in non endemic areas (including the United States). In such cases, the infection is found in Asian immigrants, or following ingestion of imported, undercooked or pickled freshwater fish containing metacercariae.

Clinical Features: Most pathologic manifestations result from inflammation and intermittent obstruction of the biliary ducts. In the acute phase, abdominal pain, nausea, diarrhea, and eosinophilia can occur. In long-standing infections, cholangitis, cholelithiasis, pancreatitis, and cholangiocarcinoma can develop, which may be fatal.

Laboratory Diagnosis: Microscopic demonstration of eggs in the stool or in duodenal aspirate is the most practical diagnostic method. The adult fluke can also be recovered at surgery. Diagnostic findings  

Microscopy Morphologic comparison with other intestinal parasites.

Treatment: Praziquantel or albendazole* are the drugs of choice. For additional information, see the recommendations in The Medical Letter (Drugs for Parasitic Infections). * This drug is approved by the FDA, but considered investigational for this purpose.

Microscopy Clonorchis sinensis eggs are small, ranging in size from 27 to 35 µm by 11 to 20 µm. The eggs are oval shaped with a convex operculum, that rests on visible "shoulders," at the smaller end of the egg. At the opposite (larger, abopercular) end, a small knob or hooklike protrusion is often visible. The miracidium is visible inside the egg.

A

B

A, B: Clonorchis sinensis eggs. The small knob at the abopercular end is visible in A. Also note the operculum resting on "shoulders" in B; image taken at 400× magnification.

Adults Clonorchis sinensis adults are flattened and measure approximately 10-25 mm long by 3-5 mm wide. Like other flukes, they are hermaphroditic, with a single ovary situated anterior to two branches testes. Adults reside in the biliary passages of the liver of the definitive host.

C

D

C: Adult of C. sinensis. D: Adult of C. sinensis stained with carmine. Clearly visible in this image are the oral sucker (OS), pharynx (PH), ceca (CE), acetabulum, or ventral sucker (AC), uterus (UT), vitellaria (VT) and testes (TE).