Opisthorchis

Opisthorchis is a genus of small parasitic flatworms in the family Opisthorchiidae, commonly referred to as liver flukes. The best known species are Opisthorchis viverrini and Opisthorchis felineus, which infect the biliary tract of humans and other mammals. Transmission occurs through ingestion of raw or undercooked freshwater fish that harbor the metacercarial stage.

The life cycle begins when eggs excreted in feces reach fresh water. In the water, eggs hatch into miracidia that infect a freshwater snail (the first intermediate host). After several developmental stages, cercariae are released and subsequently encyst as metacercariae in freshwater fish (the second intermediate host). Humans acquire infection by consuming raw or undercooked fish containing metacercariae. In the host, juvenile flukes migrate to the biliary ducts, where they mature and produce eggs that are passed in the stool.

Clinical features vary; many infections are asymptomatic. Chronic opisthorchiasis can cause biliary inflammation, cholangitis, biliary obstruction, and right upper quadrant pain. Infection with Opisthorchis viverrini is notably associated with an increased risk of cholangiocarcinoma, while Opisthorchis felineus can also cause biliary disease, though cancer risk is less clearly defined.

Diagnosis relies on stool examination for operculated eggs; serology and imaging (ultrasound or cholangiography) support diagnosis in compatible contexts. Treatment of opisthorchiasis is with praziquantel, typically given as 25 mg/kg three times daily for one day. Prevention focuses on avoiding consumption of raw freshwater fish and implementing public health measures in endemic areas.