Opisthorchiasis is a zoonotic illness caused by 2 species of liver flukes: Opisthorchis viverrini (Southeast Asian liver fluke), found in Vietnam, Thailand, Laos, and Cambodia, and Opisthorchis felineus, found in Italy, Germany, Belarus, Russia, Kazakhstan, and Ukraine.

Eggs are initially ingested by snails. These eggs hatch, and freshwater fish are infected with the cercariae. In fish, the cercariae encyst. Humans become infected after ingesting raw, undercooked, salted, pickled, or smoked freshwater fish that contains these larval parasites. Adult worms in humans live in the bile and pancreatic ducts.

The majority of patients are asymptomatic, but some patients may develop fever and abdominal pain 2-4 weeks after acute exposure. Skin findings including urticaria are rarely found. Laboratory evaluation may reveal peripheral eosinophilia. Patients who suffer with chronic infection may present with abdominal pain and weight loss. Obstruction of the bile ducts may lead to cholangitis or liver abscess.

Diagnosis is made by identifying eggs in the stool. Adult worms may be seen during endoscopic retrograde cholangiopancreatography (ERCP) or occasionally during ultrasound of the gallbladder. Treatment is with praziquantel or albendazole.

Opisthorchis viverrini infection has been associated with cholangiocarcinoma in the endemic region.