ULTRASTRUCTURE OF EARLY STAGES OF INFECTIONS IN MICE FED TOXOPLASMA-GONDII OOCYSTS

Transmission electron microscopy was used to study Toxoplasma gondii i nfections in the small intestines of Swiss-Webster mice at 2-48 h post -feeding of oocysts (p.f.). Sporozoites passed through intestinal epit helial cells (enterocytes and goblet cells) and infected all cells exc ept red blood cells in the lamina propria. Parasites in intestinal epi thelial cells or in cells in the lamina propria were located within a single type of parasitophorous vacuole, which contained exocytosed ele ctron-dense material and well-developed tubulovesicular membranous net works. Sporozoites did not infect intraepithelial lymphocytes (IELs), but at 48 h p.f. IELs had become infected with tachyzoites arising fro m those that had developed in the lamina propria. At 48 h p.f., the la mina propria contained numerous tachyzoites, much cellular debris, and few intact cells. The intestinal epithelium exhibited limited cytopat hological changes except for villar fusion, slight vacuolation, and ce ll separation at the bases of enterocytes.