Mammals acquire the infection by eating vegetation containing metacercariae. After ingestion, the metacercariae excyst in the duodenum and migrate through the intestinal wall, the peritoneal cavity and the liver parenchyma into the biliary ducts, where they develop into adults. Fasciola hepatica infect various animal species, mostly herbivores. Humans can become infected by ingesting metacercariae-containing freshwater plants, especially watercress. In humans, maturation from metacercariae into adult flukes takes approximately 3 to 4 months.
Fascioliasis occurs worldwide.
Human infections with F. hepatica are found in areas where sheep and cattle are raised, and where humans consume raw watercress, including Europe, the Middle East, and Asia. Infections with F. gigantica have been reported, more rarely, in Asia, Africa, and Hawaii.