Fasciola hepatica cercaria, scanning electron micrograph (SEM). Fasciola hepatica, also known as the common liver fluke or sheep liver fluke, is a parasitic trematod ( fluke or flatworm, a type of helminth) that infects the livers of various mammals, including humans. F.hepatica is distributed worldwide, and causes great economic losses in sheep and cattle.To complete its life cycle F.hepatica requires a freshwater snail as an intermediate host. From the snail, minute cercariae emerge and swim through pools of water in pasture, and encyst as metacercariae on near-by vegetation.The metacercariae are ingested by the ruminant or, in some cases, by humans eating uncooked foods, such as watercress or salad, thus continuing the life cycle in the mammalian host. Magnification: x750 when printed at 10cm