CHRONIC INFECTION WITH TOXOPLASMA-GONDII DOES NOT PREVENT ACUTE DISEASE OR COLONIZATION OF THE BRAIN WITH TISSUE CYSTS FOLLOWING REINFECTION WITH DIFFERENT STRAINS OF THE PARASITE

TWO strains of Toxoplasma gondii with different capacities to induce d isease and brain lesions in mice were used to study the effects of rei nfection with the parasite on a previously infected host. In spite of marked antibody and cell-mediated immune responses, chronically infect ed mice developed disease and died of acute toxoplasmosis when reinfec ted with a strain different from the one causing the primary infection . Moreover, the marked antibody and cell-mediated immune responses of the chronically infected mice did not prevent invasion of their brains and formation of tissue cysts by the reinfecting strain. Tissue cysts of the reinfecting strain were demonstrated in the brains of the chro nically infected and subsequently reinfected mice. These results highl ight the importance of strain differences in the pathogenesis of toxop lasmosis.