Submitted to: Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 10, 1997
Publication Date: N/A
Interpretive Summary: Infections by the protozoan parasite, Toxoplasma gondii are widespread in livestock and humans. Humans become infected by ingesting uncooked meat containing tissue cysts or by ingesting food or water contaminated with the resistant form of the parasite (oocyst) excreted in the feces of infected cats. Oocyst-induced infections are more severe than tissue cyst-induced infections. Scientists at the Beltsville Agricultural Research Center and the Montana State University report electron-microscopic observations in the intestines of mice fed Toxoplasma oocysts. The results described elucidate the mechanism of production of the disease. These results will be useful to veterinary pathologists, parasitologists and public health workers.
Transmission electron microscopy was used to study Toxoplasma gondii infections in the small intestines of Swiss-Webster mice at 2-48 h post-feeding of oocysts (PF). Sporozoites passed through intestinal epithelial cells (enterocytes and goblet cells) and infected all cells except red blood cells in the lamina propria. Parasites in intestinal epithelial cells or in cells in the lamina propria were located within a single type of parasitophorous vacuole, which contained exocytosed electron-dense material and well-developed tubulovesicular membranous networks. Sporozoites did not infect intraepithelial lymphocytes (IELs), but at 48 h PF IELs had become infected with tachyzoites arising from those that had developed in the lamina propria. At 48 h PF, the lamina propria contained numerous tachyzoites, much cellular debris, and few intact cells. The intestinal epithelium exhibited limited cytopathological changes except tfor villar fusion, slight vacuolation, and cell separation at the bases of enterocytes.