The effect of sulfomethoxypyrazine-pyrimethamine therapy on the fine structure of Toxoplasma gondii-cysts in the brain of Mastomys natalensis. Scanning and transmission electron microscopical investigations.

Two month old chronically infected Mastomys natalensis, which had been treated for ten days with sulfomethoxypyrazine-pyrimethamine, were utilized for testing the effect of chemotherapy on the fine structure of Toxoplasma cysts (strain ALT). After completion of the therapy, cysts were examined from the brains of killed animals in scanning and transmission electron microscopes. The scanning electron microscopic experiments revealed no or only slight morphological differences between the cysts of the untreated controls (Fig. 1) and the treated animals (Fig 2). In transmission electron microscopic studies the cyst membrane appeared less rugged (see Fig. 3,7 and the untreated control Fig. 6). The cyst basic substance often produces an optically empty space (Fig. 3,4). The pellicle of individual parasites display an unusual affinity for the pellicle of neighboring parasites (Fig. 3,5,7). In direct contrast to the untreated cysts no endodyogeny could be observed on the treated cysts examined to this point.