Clonorchis

Clonorchis is a genus of digenetic trematodes in the family Opisthorchiidae, with Clonorchis sinensis (the Chinese liver fluke) as the best known species to infect humans. Adult worms inhabit the biliary ducts of the liver and gallbladder, where they produce eggs that are excreted in feces.

The life cycle begins when eggs reach freshwater and are ingested by a suitable snail (the first intermediate host). Inside the snail, parasites undergo larval development and release free-swimming cercariae, which then infect freshwater fish (the second intermediate host) and encyst as metacercariae in fish tissues. Humans and other fish-eating mammals become infected by consuming raw or undercooked infected fish. Metacercariae excyst in the duodenum and migrate to the biliary tree, where they mature and lay eggs.

Most infections are asymptomatic, but heavier infections can cause biliary irritation, epigastric or right upper quadrant pain, hepatomegaly, and abnormal liver function tests. Chronic clonorchiasis is associated with cholangitis, biliary stones, and an increased risk of cholangiocarcinoma.

Diagnosis relies on detection of characteristic eggs in stool or bile samples, supported by imaging or serology in some cases. Treatment typically uses praziquantel, with albendazole as an alternative. Management also includes treating complications as needed.

Geographically, clonorchiasis is endemic in East Asia, including parts of China, Korea, Vietnam, and Russia’s Far East, and can occur via travel or importation of raw fish. Prevention centers on avoiding raw or undercooked freshwater fish, proper cooking, sanitation to prevent contamination of water with feces, and control of intermediate hosts where feasible.