Cryptosporidium and Isospora

The coccidian Cryptosporidium spp., Isospora belli, Sarcocystis suihominis and S. bovihominis are intestinal parasites of humans. Coccidia are obligate parasitic intracellular protozoa, with a typical apical complex seen with the electron microscope. There are species with a single host (monoxenous) and species with a definitive (or final) host and an intermediate host (heteroxenous). The parasite specificity is higher to the final host, in which the sexual multiplication and the formation of the oocyst containing the infective stages (sporozoites) take place. Asexual endogenous or tissue stages develop in the intermediate host.