Evaluation of the effects of sulfamethoxazole on Toxoplasma gondii loads and stage conversion in IFN-γ knockout mice using QC-PCR

Toxoplasma gondii abundance with or without sulfamethoxazole treatment was evaluated by quantitative competitive polymerase chain reaction (QC-PCR) assay in various organs of IFN-gamma knockout BALB/c (B/c) mice after peroral infection with the cyst-forming Fukaya strain. T gondii infection was observed in the brain, skin, tongue, heart, and skeletal muscle of the mice treated with sulfamethoxazole, although the parasite was not observed during the treatment in the mesenteric lymph node, spleen, small intestine or kidney. After discontinuing the therapy, T gondii reappeared within five days in all organs. Reverse transcriptase (RT)-PCR showed that sulfamethoxazole treatment accelerated the stage conversion of T gondii from tachyzoites into bradyzoites in the brain, lung, and heart. In contrast, after discontinuing sulfamethoxazole treatment, T gondii underwent stage conversion from bradyzoites into tachyzoites in these organs. These results indicate that we successfully established an animal model for evaluating chemotherapy regimens in immunocompromised hosts infected with T. gondii.