Interrelations of a low-virulence strain of Toxoplasma gondii and inbred mice during late periods of observation

Distinct differences in the intensity and dynamics of the infection with cysts of toxoplasms of law virulent (Czech) strain of brain of mice of three different pure lines and strainless ones differing in the sensitivity to the agent during a chronic period of infection have been noted. In sensitive mice of AKR line the period of formation and growth of cysts as well as the period of their elimination from the brain is longer than in less sensitive ones. In this connection cysts in the brain of these mice turned out to be larger than in the brain of less sensitive mice of CC57BR line. Activation of the infection in the brain, revealed microscopically, is observed most commonly in mice of AKR line (40%), more seldom in CC57BR (9.1%) and strainless ones (7.7%) and is not observed at all in resistent BALB/c. Lethality of these mice was by 9 months of infection 87, 40, 41 and 5.3%, respectively. 1-1.5 year after the infection in animals without relapses the infection level of brain was equally low.