clonorchiasis

Clonorchiasis is a parasitic infection of the biliary tract caused by the liver fluke Clonorchis sinensis. Humans acquire the infection by ingesting raw or undercooked freshwater fish that harbor metacercariae. The disease is most common in East Asia but has been reported in other regions through travel or immigration.

The life cycle begins with eggs excreted in human or animal feces reaching freshwater. Freshwater snails serve as the first intermediate host, where the parasite develops and releases cercariae, which then infect fish as the second intermediate host. Humans become infected by consuming raw or undercooked fish containing metacercariae. In the human host, the metacercariae migrate to the intrahepatic bile ducts and mature into adult flukes.

Clinical features vary; many infections are asymptomatic. When symptoms occur, they are nonspecific and may include dyspepsia, right upper quadrant discomfort, nausea, and fatigue. Heavy infections can cause biliary obstruction, cholangitis, and pancreatitis. Chronic clonorchiasis is associated with ongoing biliary inflammation and fibrosis and increases the risk of cholangiocarcinoma, particularly with prolonged exposure.

Diagnosis relies on stool examination for parasite eggs, which are small and operculated with a knob. Serology or antigen detection can aid in some cases. Imaging modalities such as ultrasound, CT, or MRCP may show dilated or irregular intrahepatic ducts; ERCP can assist in diagnosis and management.

Treatment and prevention: praziquantel is the drug of choice, with a common regimen of 25 mg/kg three times daily for one day. Alternatives such as albendazole may be used where praziquantel is unavailable or contraindicated. Prevention focuses on avoiding raw or undercooked freshwater fish, along with general sanitation and public health measures to reduce transmission.