Fasciola Hepatica - Life Cycle

Life Cycle

To complete its life cycle, F. hepatica requires a freshwater snail as an intermediate host, such as Galba truncatula, in which the parasite can reproduce asexually.

Species in the family Lymnaeidae that serve as naturally or experimentally intermediate hosts of Fasciola hepatica include: Austropeplea tomentosa, Austropeplea ollula, Austropeplea viridis, Radix peregra, Radix lagotis, Radix auricularia, Radix natalensis, Radix rubiginosa, Omphiscola glabra, Lymnaea stagnalis, Stagnicola fuscus, Stagnicola palustris, Stagnicola turricula, Pseudosuccinea columella, Lymnaea viatrix, Lymnaea neotropica, Fossaria bulimoides, Lymnaea cubensis, Lymnaea sp. from Colombia, Galba truncatula, Lymnaea cousini, Lymnaea humilis, Lymnaea diaphana, Stagnicola caperata and Lymnaea occulta.

Adult hepatica lives in bile passages of the liver of many kinds of mammals, especially ruminants. Humans are occasionally infected. In fact, fascioliasis is one of the major causes of hypereosinophilia in France. The flukes feed on the lining of biliary ducts. Their eggs are passed out of the liver with bile and into the intestine to be voided with feces. If they fall into water, eggs will complete their development into miracidia and hatch in 9 to 10 days during warm weather. Colder water retards their development. On hatching, miracidia have 24 hours in which a find a suitable snail host. Mother sporocysts produce first generation rediae, which in turn produce daughter rediae that develop in snail's digestive gland. From the snail, minute cercariae emerge and swim through pools of water in pasture, and encyst as metacercariae on near-by vegetation. From here, the metacercariae are ingested by the ruminant, or in some cases, by humans eating uncooked foods such as watercress. Contact with low pH in the stomach causes the early immature juvenile to begin the process of excystment. In the duodenum, the parasite breaks free of the metacercariae and burrows through the intestinal lining into the peritoneal cavity. The newly excysted juvenile does not feed at this stage, but once it finds the liver parenchyma after a period of days, feeding will start. This immature stage in the liver tissue is the pathogenic stage, causing anaemia and clinical signs sometimes observed in infected animals. The parasite browses on liver tissue for a period of up to six weeks, and eventually finds its way to the bile duct, where it matures into an adult and begins to produce eggs. Up to 25,000 eggs per day per fluke can be produced, and in a light infection, up to 500,000 eggs per day can be deposited onto pasture by a single sheep.