Common Liver Fluke – Life Cycle

The common liver fluke (*Fasciola hepatica*) is an internal parasite of mammals with a complex life cycle involving two host species. Adult flukes reside in the bile ducts of cattle, sheep and wild game, though they can occasionally infect humans. Fluke eggs are expelled in the feces of these host animals. When the eggs reach water, they release small, ciliated larvae called miracidia, which then penetrate freshwater snails, which are the first temporary hosts in the liver fluke's life cycle. Miracidia penetrate freshwater snails, which are Common Liver Flukes' first temporary hosts. Inside the snail, the miracidia develop into sporocysts, which then asexually produce multiple rediae. These rediae, in turn, produce cercariae, which have a mobile "tail" that allows them to leave the snail and swim freely in the water. Cercariae attach to vegetation, such as grass, and encyst to form a protective metacercaria. The metacercaria, with its hard outer layer, can survive outside water. The life cycle completes when a final host ingests grass contaminated with metacercariae.