Scanning and transmission electron microscopic observations on the host-parasite relationship in intestinal cryptosporidiosis of neonatal calves.

The association of cryptosporidia with the intestinal epithelium of three neonatal calves was studied by scanning (SEM) and transmission (TEM) electron microscopy. Trophozoites and schizonts were observed embedded in the microvillous brush border of epithelial cells. Merozoites, released from schizonts, were seen free in the lumen and penetrating epithelial cells by SEM and TEM. Incorporation of microvilli into the parasitophorous envelope of trophozoites was seen by TEM. These findings indicate that cryptosporidia develop at an intracellular position in the apex of the epithelial cells following merozoite penetration.