Opisthorchiasis

Opisthorchiasis is a liver fluke infection caused by Opisthorchis viverrini (Southeast Asia: Thailand, Laos, Cambodia, Vietnam) and Opisthorchis felineus (Eastern Europe, Siberia, Kazakhstan), acquired by eating raw or fermented fish.

• About 10 million infected with O. viverrini; northeastern Thailand has the world's highest incidence of cholangiocarcinoma.
• Chronic infection causes periductal fibrosis, and is strongly linked to cholangiocarcinoma (IARC Group 1).
• Transmission maintained by cultural eating habits (koi pla, pla ra) and sanitation.

• Mostly asymptomatic; acute phase may cause fever, abdominal pain, and eosinophilia (more in O. felineus).
• Chronic symptoms: dyspepsia, right upper quadrant pain, hepatomegaly, cholangitis, cholecystitis, and biliary obstruction.
• Complications: pyogenic cholangitis, hepatic abscess, pancreatitis, periductal fibrosis, and cholangiocarcinoma.

• Stool examination for eggs (small, operculated); formalin ether concentration; indistinguishable from other small trematodes (Clonorchis, heterophyids).
• Urine and stool antigen detection and PCR; serology (ELISA).
• Ultrasound: periportal fibrosis ("starry sky"), gallbladder enlargement, and bile duct dilatation; MRCP or CT.
• CA 19-9 and imaging if cholangiocarcinoma is suspected.
• Exclude clonorchiasis, fascioliasis, sclerosing cholangitis, and gallstone disease.

• Praziquantel 40 mg/kg as a single dose (O. viverrini), or 25 mg/kg three times daily for 2 days for O. felineus; cure rate about 90 to 95%.
• Repeat stool tests at 4 to 6 weeks; re-treat if positive.
• Treat complications: antibiotics for cholangitis, ERCP drainage, and surgery for cholangiocarcinoma.
• Ultrasound screening programmes for early detection of cholangiocarcinoma in endemic communities.
• Prevention: cooking fish thoroughly (freezing at -20 degrees Celsius for 7 days), health education, sanitation, and regular mass drug administration (praziquantel).