Liver flukes belonging to the class Trematoda — for example, Fasciola hepatica, the common liver fluke. Trematodes are parasitic flatworms with complex life cycles involving snails and vegetation; humans acquire fascioliasis by eating contaminated watercress or other aquatic plants bearing encysted larvae. The flukes migrate to the liver, causing inflammation and bile-duct damage. Food-safety prevention centres on snail control in pastures, avoiding raw aquatic vegetables from endemic areas, and — for livestock — flukicide treatment with withdrawal periods. Thorough cooking of risky produce destroys the infective cysts.