PARASITEMIA AND PARASITIC LOADS IN ACUTE INFECTION AND AFTER ANTI-GAMMA-INTERFERON TREATMENT IN A TOXOPLASMIC MOUSE MODEL

Toxoplasma gondii infection was induced in Swiss-Webster mice by intra peritoneal inoculation of avirulent Beverley strain cysts. We studied parasitemia and parasitic loads first in acute toxoplasmosis, then in the chronic stage of the disease. In the latter stage a group of mice received weekly administration of a rabbit antiserum directed against mouse gamma-interferon. Parasitemia, sequentially determined by amplif ication of the B1 gene using polymerase chain reaction, persisted for more than 1 month in acute toxoplasmosis. Brain and lung parasitic loa ds, assessed by a tissue-culture method, were significantly increased in mice treated with anti-interferon. Moreover, this increase was prev ented by concomitant administration of pyrimethamine and sulfadiazine, suggesting that early prophylaxis would be suitable. Surprisingly, th e anti-interferon treatment induced neither abnormal clinical signs no r a significant rise in the parasitemia level. Such a model seems to b e particularly appropriate for the comparison of different strains of Toxoplasma gondii in a moderately immunodeficient state.