Cryptosporidium parvum (Coccidia, apicomplexa):: Some new ultrastructural observations on its endogenous development

Some new ultrastructural data have been presented on the endogenous development of Cryptosporidium parvum, examined in vivo in experimentally infected rats. These data are aimed to supplement the previous knowledge on the life cycle of this homoxenous coccidian parasite. The asexual reproduction of C. parvum was confirmed to fit the pattern of exogenesis of other coccidia, with an obvious peculiarity being the involvement of a trimembranous pellicle in the formation of merozoite anlagen. In the daugther merozoites of C. parvum mitochondria were first reported. The unique extracytoplasmic position of endogenous stages of Cryptosporidium, along with establishment of the feeder organelle and dense band, have been first demonstrated in C. parvum-infected intraepithelial macrophages of rat ileum. The peculiar parasitophorous vacuole is limited by two membranes of macrophage lamellipodia closely apposed to each other and thus incorporating the growing parasites, the outer membrane of this vacuole being in continuity with the host cell membrane. Besides, intact and partially digested C. parvum organisms were seen deep within the cytoplasm of some free macrophages in the ileal lumen, being presumably passively phagocytosed.