Submitted to: International Journal for Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 3, 2004
Publication Date: February 15, 2005
Citation: Speer, C.A., Dubey, J.P. 2005. Ultrastructural differentiation of Toxoplasma gondii schizonts (types b to e) and gamonts in the intestines of cats fed bradyzoites. International Journal for Parasitology. 35:193-206.
Interpretive Summary: Infection by the single-celled parasite Toxoplasma gondii causes mental retardation in children and abortion in livestock. Cats are the main reservoirs of infection. Scientists at the Beltsville Agricultural Research Center and the University of Tennessee report for the first time ultrastructure of Toxoplasma in the intestines of cats. These results will be of interest to biologists and parasitologists.
The ultrastructural characterisitics of four types of Toxoplasma gondii schizonts (types B, C, D and E) and their merozoites, microgamonts and macrogamonts were compared in cats killed at days 1, 2, 4 and 6 days after feeding tissues cysts from the brains of mice. Schizonts, merozoites and gamonts contained most of the ultrastructural features characteristic of the phylum Apicomplexa. All four types of schizonts developed within enterocytes or intraepithelial lymphocytes. Occasionally, type B and C schizonts developed within enterocytes that were displaced beneath the epithelium into the lamina propria. Type D and E schizonts and gamonts developed exclusively in the epithelium. Tachyzoites occurred exclusively within the lamina propria. Type B schizonts formed merozoites by endodyogeny, whereas types C-E developed by endopolygeny. The parasitophorous vacuoles surrounding type B and C schizonts consisted of a single membrane, whereas those surrounding types D and E schizonts were comprised of 2 to 4 electron-dense membranes. The parasitophorous vacuole of type B schizonts had an extensive tubulovesicular membrane network (TMN); the TMN was reduced or absent in type C schizonts and completely absent in types D and E schizonts and gamonts. Type B merozoites were ultrastructurally similar to tachyzoites, except that they were slightly larger. Type C merozoites exhibited a positive periodic acid-Schiff reaction by light microscopy and ultrastructurally contained amylopectin granules. Rhoptries were labyrinthine in type B merozoites but were electron-dense in types C-E. The early development of microgamonts, macrogamont and oocysts is also described.