Activity of diclazuril against Toxoplasma gondii in cultured cells and mice.

The capability of diclazuril, a benzeneacetonitrile anticoccidial agent, to inhibit development of tachyzoites of Toxoplasma gondii was examined in cultured human foreskin fibroblast cells and in Hsd:ICR mice. Treatment of infected cell cultures with 10.0, 1.0, 0.1 or 0.01 microgram of diclazuril/ml for 3 days resulted in > 99% reduction in tachyzoite counts, compared with controls. Treatment with 0.005 microgram of diclazuril/ml resulted in > 97% reduction in tachyzoite counts, compared with controls. Treatment of host cells with 10.0, 1.0, 0.1 and 0.01 microgram of diclazuril/ml for 24 hours prior to tachyzoite inoculation resulted in 97, 31, 0, and 0% reduction in tachyzoite counts, compared with controls, respectively, 3 days after inoculation. All mice that were treated orally with 10.0 mg of diclazuril/kg of body weight and 80% of mice treated orally with 1.0 mg of diclazuril/kg 1 day prior to and for 10 days after tachyzoite inoculation were protected against acute toxoplasmosis. Mice treated with 10.0 mg of diclazuril/kg did not develop protective immunity, whereas mice treated with 1.0 mg of diclazuril/kg survived challenge exposure.