Cestodes live as intestinal parasites firmly attached to the mucosa of the gut in their definitive hosts where they can live for years (e.g., Taeniasis, Animals, Taeniasis, Man). Gravid proglottids or eggs are released in the feces and ingestion of eggs by susceptible intermediate hosts results in the release of larvae, also called oncospheres within the gastrointestinal tract. The oncospheres penetrate the intestinal mucosa and migrate into tissues of the host where they can develop into mature metacestodes (e.g., Cysticercosis, Echinococcosis). Important cestode infections are listed in Platyhelminthic Infections, Man, Pathology.
While relatively little is known on immunity against the adult tapeworms in the gut, mechanisms of host-parasite interactions and the immune response have been extensively studied for the tissue stages. In larval cestode infections the intermediate mammalian host harboring egg-derived metacestodes in the tissues becomes completely immune to reinfection with eggs. In contrast, autoinfections with eggs occur in the case of Taenia solium when the host is initially infected with metacestode-derived adult tapeworms in the gut lumen.