Liver flukes infect the liver, gallbladder, and bile duct in humans. While most infected persons have no symptoms, infections that last a long time can result in severe symptoms and serious illness. Infections are not known to last longer than 25–30 years, the life span of the parasite.
People become infected by eating raw or undercooked freshwater fish containing the larvae. Lightly salted, smoked, or pickled fish may contain infectious parasites. Drinking river water or other nonpotable water will not lead to infection with Opisthorchis.
The eggs of Opisthorchis viverrini are ingested by snails in fresh water. After the eggs hatch, infected snails will release microscopic larvae that can enter freshwater fish. People become infected when eating raw or undercooked fish that contains the parasite. After ingestion, the liver flukes grow to adult worms that live inside the human bile duct system. The life cycle takes three months to complete in humans. Infected people will then pass eggs in their stool or may cough them up.