Trichinella

In this unusual life cycle one individual serves as both definitive and intermediate host. Adults live intercellularly within the mucosa of the small intestine of birds and mammals. After mating the female gives birth to first stage larvae and deposits them into venules. The L1 are distributed throughout the body and penetrate skeletal muscle cells. They cause the muscle cell to be transformed into a nurse cell within which the parasite grows and awaits ingestion by another host. It takes about 1 month for these intracellular "muscle larvae" to become infective.

When eaten by another host, the muscle larvae are digested out of the muscle tissue. They enter the mucosa of the intestine and undergo four rapid molts, reaching the adult stage in about 1 week. The adults live only a few weeks before they are expelled by the host's immune response.