The organism known as Fasciola hepatica is a type of fluke, which is a parasitic trematode. Fasciola hepatica infects snails and mammals, causing the disease known as fascioliasis. Because the parasite is often discovered in captive sheep, it is sometimes called the sheep liver fluke. The species lives all over the world.
These flukes have a complex life cycle that begins in aquatic and semiaquatic snails. When the snail defecates, the flukes exit the snail’s body and take refuge on the stems and leaves of aquatic and terrestrial plants. When mammals eat the contaminated plants, the flukes make their way into the mammals’ digestive systems and ultimately into the liver. People normally acquire sheep liver flukes by ingesting raw watercress or other aquatic plants that are coated with Fasciola hepatica eggs.
Sheep liver flukes are very large flukes, with some reaching up to 30 millimeters in length and 13 millimeters in width. They are lance- or leaf-shaped and feature spines all over their bodies. They are variable in color and each fluke has a small oral disk at one end of its body.
Fascioliasis is easily prevented by cooking or washing vegetables before they are eaten. However, when infections do occur, they are relatively easy to treat and most people recover without long-term consequences.