Clonorchis sinensis

Clonorchis sinensis egg  Photo/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

Geography

• 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

Pathology

• 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)

Diagnosis

• Finding the characteristic eggs in feces or duodenal aspirate

Treatment

• Praziquantel or albendazole are the drugs of choice

Epidemiology

• 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

Prevention

• 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

C. sinensis adult

Photo/Banchob Sripa, Sasithorn Kaewkes, Paiboon Sithithaworn, Eimorn Mairiang, Thewarach Laha, Michael Smout, Chawalit Pairojkul, Vajaraphongsa Bhudhisawasdi, Smarn Tesana, Bandit Thinkamrop, Jeffrey M. Bethony, Alex Loukas & Paul J. Brindley via Wikimedia Commons