Parasitology 101 is an educational blog that that can be used as a study guide for microbiology, infectious disease and medical technology students. The “bullet-point” format keeps the information concise and to the point.

clonorchis egg/CDC
clonorchis egg/CDC

General Information

  • Clonorchis sinensis is a trematode or fluke also known as the “Chinese liver fluke” or “Oriental liver fluke”
  • Clonorchiasis is a trematode disease of the bile ducts
  • Adult flukes produce an estimated 4,000 eggs per day per worm


  • Asia only
  • Mainland China, highly endemic in southeastern China
  • Taiwan, Korea, Vietnam
  • Reports outside of Asia are important (imported cases)

Morphology (adults)

  • Slender, pointed anterior, rounded posterior
  • 1-2 cm long and 3-5 mm wide
  • Characteristic branching testes posterior

Morphology (eggs)

  • Small, 26-30 x 15-17 um
  • Ovoid, yellowish color
  • Operculated at one end, small knob at opposite end

Life Cycle

  • Adults in biliary ducts, embryonated eggs pass to intestine and out with the feces
  • Eggs reach water, ingested by suitable snail (P. manchouricus)
  • In the snail (first intermediate host, eggs release miracidium and goes through several stages in host (sporocyst>rediae>cercariae)
  • Cercariae released from snail, free-swimming in water, penetrates under scales of an appropriate freshwater fish (second intermediate host)
  • Metacercariae encyst in the fish muscle
  • Humans infected by eating raw, partially cooked, smoked or pickled fish
  • Metacercariae excysts in the duodenum
  • Ascends up through intestine to bile ducts
  • Matures to adult in 30 days
  • Worms may live 30-40 years in final host
  • Carnivorous animals can serve as reservoir hosts


  • Most infections are asymptomatic
  • More progressive infections may see anorexia, jaundice, diarrhea, epigastric pain, fever
  • Some infections associated with severe complications: pancreatitis, cholangitis and cholangiocarcinoma (bile duct cancer)


  • Finding the characteristic eggs in feces or duodenal aspirate


  • Praziquantel or albendazole are the drugs of choice


  • Clonorchiasis is endemic where there is poor sanitation, and
  • The right snail host, and
  • The right fish (cyprinoid fish) as the second intermediate host, and
  • A population who eats raw, poorly pickled, smoked, dried or salted freshwater fish


  • Thoroughly cook all freshwater fish, irradiate or freeze at -10C for at least 5 days
  • Educate the public in endemic areas about the dangers of eating raw or improperly cooked fish
  • Proper disposal of feces