Liver fluke. Illustration of an adult liver fluke (Fasciola hepatica), a parasite of sheep, cattle and humans. Humans ingest the fluke larvae by eating infested vegetation. Immature flukes penetrate the intestinal wall and pass into the bile ducts via the liver. They mature whilst ingesting blood and tissue debris. About 3 or 4 months after infection, the flukes produce eggs which pass into the faeces, and so pass out of the body to contaminate lakes and streams. The eggs hatch to release larvae which infect certain snails. A free-swimming form released from the snails becomes encysted on aquatic vegetation, forming the next infective stage.