Genetic resistance against acute toxoplasmosis depends on the strain of Toxoplasma gondii.

The role of the strain of Toxoplasma gondii in genetic control of resistance against acute infection with T. gondii was studied with 2 strains of T. gondii, which differ in their virulence and genotype. Following peroral infection with 10 cysts of the C56 strain, C57BL/6 (H-2b) and C3H/HeN (H-2k) mice died significantly earlier than BALB/c mice (H-2d) mice, although all of the mice eventually died of acute toxoplasmosis from 10 to 23 days after infection. There was no significant difference in time to death between C57BL/6 mice and C3H/HeN mice. In peroral infection with 100 cysts of the less virulent ME49 strain, all C57BL/6 mice died of acute toxoplasmosis from 7 to 10 days after infection. C57BL/6 mice died significantly earlier following infection with the ME49 strain than with the C56 strain, whereas all C3H/HeN mice infected with the ME49 strain survived as did BALB/c mice. These results indicate that genetic control of resistance against acute infection with T. gondii differs depending on the strain of T. gondii.