Structural changes of Toxoplasma gondii bradyzoites and cysts following therapy with sulfamethoxypyrazine-pyrimethamine: studies by light and electron microscopy. Consequences for chemotherapy.

Mastomys natalensis chronically infected with Toxoplasma gondii strain ALT over two months were treated with sulfamethoxypyrazine-pyrimethamine for 10 and 25 days. 72 hours after discontinuation of therapy the animals were sacrificed. The brains were removed and, following corresponding preparation, studied for the presence of the parasite and structural changes of cysts by light and transmission electron microscopy. More or less pronounced structural changes could be found in cyst walls, bradyzoites, and in particular in the endodyogeny stages. The degree of damage proved to be proportional to the intensity of the bradyzoite metabolism. The combination of drugs used was capable of passing the cyst membrane as long as the bradyzoites maintained their metabolism irrespective of its intensity. In cysts with a largely dormant metabolism that had been subject to therapy, no micromorphological differences of the ultrastructure could be recognized when compared with untreated controls of identical age; these cysts could not be influenced by treatment.