[Electron microscopic research on Cryptosporidium. I. The asexual stages in the development of Cryptosporidium parvum].

Ultrastructural studies were conducted on asexual developmental stages of C. parvum in the ileal fragment of the intestine of 10-11 day old rats experimentally infected with oocysts isolated from calf feces. A young trophozoite is covered with the typical trimembranous apicomplexan pellicle. As the parasite grows, the inner complex of its apical pellicle, facing the host enterocyte, is seen to reduce up to a unit membrane to make a complex multimembranous "feeding organelle" which is in contact with a thick electron dense band bordering the host-parasite interface. It looks likely that no micropores or any other feeding structures exist in the parasite. Unlike, the opposite body part of the trophozoite, facing the lumen of the intestine, preserves its trimembranous pellicle. Two merozoite generations were followed. In addition to numerous ribosomes, rhoptries, micronemes, and trimembranous pellicle, subpellicular microtubules were observed in the segmenting merozoites. The merogony follows the pattern of ectomeric schizogony. However, no details of nuclear division were detected. The whole cytoplasm of the mother meront is completely used up for the merozoite formation without any residual mass to be left.