Clonorchiasis and opisthorchiasis are caused by similar liver flukes (parasitic flatworms) which reside in the bile ducts and infect humans through the ingestion of raw or inadequately cooked or pickled freshwater fish (saltwater fish do not carry these parasites).
A majority of persons with clonorchiasis and opisthorchiasis are infected with few parasites and present no signs or symptoms. If acute symptoms do occur they include: general tiredness, fever and abdominal pain. Chronic symptoms include weakness, lack of appetite, abdominal pain, diarrhoea, prolonged low-grade fever and jaundice (yellow pigmentation of skin).
Opisthorchiasis occurs in Asia, Eastern Europe, Russia and the former Soviet republics.