The trematode Clonorchis sinensis (Chinese or oriental liver fluke).
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.
Endemic areas are in Asia including Korea, China, Taiwan, and northern 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.
Most infections are asymptomatic. Most pathologic manifestations result from inflammation and intermittent obstruction of the biliary ducts. In mild cases, manifestations include dyspepsia, abdominal pain, diarrhea or constipation. With infections of longer duration, the symptoms can be more severe, and hepatomegaly and malnutrition may be present. In rare cases, cholangitis, cholecystitis, and chlolangiocarcinoma may develop.
Clonorchis sinensis eggs.
Figure A: C. sinensis egg: the small knob at the abopercular end is visible in this image.
Figure B: C. sinensis egg. Note the operculum resting on "shoulders;" image taken at 400× magnification.
Figure C: C. sinensis egg; images taken at 400× magnification.
Figure D: C. sinensis egg; images taken at 400× magnification.
C. sinensis adults.
Figure A: Adult of C. sinensis.
Figure B: 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).
Snail intermediate hosts of C. sinensis.
Figure A: Shells of Parafossarulus manchouricus, the most common snail host of C. sinensis in endemic areas in southeast Asia. Image courtesy of the Web Atlas of Medical Parasitology and the Korean Society for Parasitology.
Figure B: Bithynia sp., another common intermediate host of C. sinensis. Image courtesy of Michal Maňas.
Diagnosis is based on microscopic identification of eggs in stool specimens. However, the eggs of Clonorchis are practically indistinguishable from those of Opisthorchis. The adult fluke can also be recovered at surgery.
Serologic testing is currently not available for Clonorchis infection in the United States.
Treatment information for clonorchiasis can be found at: https://www.cdc.gov/parasites/clonorchis/health_professionals/index.html
DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.
- Page last reviewed: February 20, 2018
- Page last updated: February 23, 2018
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