The tapeworm life cycles differ from one another more so than those of the flukes. For some species, a mammal is the host of the adult stage as well as the larval stages (usually a different mammal). For that reason, when we discuss tapeworm infections, we find that humans can not only be hosts to the adult tapeworm in the intestines, but occasionally can be accidental hosts of the larval stage, which can be a much more dangerous situation.
The life cycle is always the following and is obligatory (i.e. whoever ingests the egg gets the larva, and who ingests the larva gets the adult).
To the right are some representative life cycles.
1. Life cycle of Taenia spp. Note that the human can accidentally host the larval form (cysticercus) of the pork tapeworm T. solium, but not the larval form of the beef tapeworm T. saginata.
2. Life cycle of the fish tapeworm Diphyllobothrium spp. The human can be the definitive host but can also accidentally host the larval form (plerocercoid).
