Effectiveness of spiramycin in murine models of acute and chronic toxoplasmosis

The antitoxoplasmic activity of spiramycin (SPI) was evaluated in murine models of infection using a type-1 (RH) or type-2 (Me49) strain of Toxoplasma gondii. In mice infected with 102 tachyzoites of the RH strain, treatment with 100 and 200 mg SPI/kg/day had only a limited effect; despite some dose-dependent prolongation of survival, it was unable to protect mice against death. In contrast, in acute infection induced by peroral inoculation of 10, but not 20, cysts of the Me49 strain, a 3-week course of 100 mg SPI/kg/day and a 4-week course of 200 mg/kg/day significantly enhanced protection and markedly reduced brain cyst burdens at 6 months post infection (p.i.). In chronic infection established by inoculation of 10 cysts 3 months previously, a 3-week course of 200 mg SPI/kg/day resulted in significantly decreased brain cyst burdens compared with controls, both 2 weeks after treatment cessation and by 6 months p.i. Although a favourable effect on chronic infection may be specific for mice, these data merit investigation, since they may have clinical ramifications.