Like other flukes, the liver flukes need intermediate hosts and as a result, the transmission from animals to humans happens in three phases. The first phase is the infection of the snail (the first intermediate host) via feces. They complete their gestation and hatch as cercariae. They leave their snail hosts and infect fish who are their second intermediate host. Lastly, humans ingest the metacercariae in raw and undercooked fish. In humans, the metacercariae complete their life cycle and become full grown liver flukes. Infections
Human infections are most common in Asia, Africa and Latin America. However, trematodes can be found anywhere where untreated human waste is used as fertilizer. Humans can be infected by trematodes either by consuming undercooked contaminated fish or plants, or by ingesting contaminated water. The metacercariae of trematodes attach to fish and plants. In addition, humans can be infected by certain species through swimming in contaminated water. Humans cannot get infected by trematodes directly, trematodes require an intermediate host to do so.Schistosomiasis (also known as bilharzia, bilharziosis or snail fever) is an example of a parasitic disease caused by one of the species of trematodes (platyhelminth infection, or "flukes"), a parasitic worm of the genus Schistosoma. Clonorchis, Opisthorchis, Fasciola and Paragonimus species, the foodborne trematodes, are another. Other diseases are caused by members of the genus Choledocystus. Medically, trematodes are often classed by which organ they invade, which can include blood vessels, the gastrointestinal tract, lungs, or liver.
They are adapted to recognize and penetrate the second intermediate host, and contain behavioral and physiological adaptations not present in earlier life stages. The metacercariae are an adapted cystic form dormant in the secondary intermediate host. The adult is the fully developed form which infects the definitive host.The first stage is the miracidium that is triangular in shape and covered by a ciliated ectoderm which is the outermost layer of the three germ layers. The epidermis and epidemic tissues of the parasite are going to evolve from the miracidium. They also have an anterior spin which helps them drill into the snail. The miracidium develops into the sporocyst, which is a sac-like structure, and in this sac the larvae begin to develop. The cells multiply. The rediae and cercariae develop from the larvae which are then released and encyst as metacercariae on aquatic plants. Humans as well as larger sea creatures then get infected when they eat these plants. When they infect humans, it takes 3–4 months for the metacercariae to mature into adult flukes and lay eggs. Life cycle of liver flukes
Liver flukes, one of the different species, are responsible for causing liver fluke disease which is also known as fasciolosis. They are hermaphroditic internal parasites. They are caused by the migration of a large number of immature flukes through the liver passageway or by adult flukes that migrate to the bile ducts. Liver flukes infect all grazing animals and are passed from human to human when they eat raw or undercooked fish.