During the lifecycle Fasciola hepatica(liver fluke) infects its intermediate host and primary host at the following larval stages respectively:

Explanation

The life cycle of F. hepatica is completed in two hosts. The primary host, in which the adult fluke lives, is a sheep, while the intermediate host, in which numerous larval stages are passed, is a snail (Lymnaea, Planorbis, etc.). This type of life cycle involving two different kinds of hosts is as termed digenetic. Miracidium larva is the larval stage involved in the life cycle. When suitable conditions become available, the encapsulated embryo differentiates into a miracidium larva in 415 days. It hatches out and swims in water. Metacercaria develops into adult fluke only inside its definitive host i.e sheep. The latter gets an infection by grazing on leaves and grass blades to which the cysts are attached. Metacercaria survives action of its host's gastric juices as its cysts are insoluble in them. The cyst wall finally dissolves in the proximal part of the intestine and liberates the larva.