EARLY KINETICS OF TOXOPLASMA-GONDII INFECTION IN MICE INFECTED ORALLYWITH CYSTS OF AN AVIRULENT STRAIN

We determined the early kinetics of Toxoplasma gondii infection in Swi ss Webster mice inoculated with the avirulent C strain by counting par asites in the blood, spleen, Peyer's patches, liver, lungs, and brain. Animals were orally inoculated with cysts on day zero (D0), and paras ites were counted using a tissue culture method at 12, 24, and 36 hr a nd 2, 3, 7, 10, 14, 21, 30, 50, and 72 days postinfection. The spleen and Peyer's patches were the first organs found parasitized, on D2 and D3, respectively, followed by the lungs and liver on D7 and the brain on D10. No parasitemia was detected. This suggests that early dissemi nation of this avirulent strain from the intestine into the general ci rculation occurs essentially via the lymphatic system. Parasites persi sted at a high level in the brain during the chronic phase. In the lun gs, parasites were no longer detected by D72, while parasite numbers i nitially declined in the spleen and Peyer's patches but then showed a second peak, possibly due to recirculation of T. gondii. These results suggest that lymphoid organs play a key role in T. gondii disseminati on during the acute phase and may also constitute a persistent source of parasite resurgence.