TOXOPLASMA-GONDII - KINETICS OF THE DISSEMINATION IN THE HOST TISSUESDURING THE ACUTE-PHASE OF INFECTION OF MICE AND RATS

Mice and rats differ in their susceptibility to Toxoplasma gondii infe ction. Here we have compared the parasitological parameters of acute i nfection in both mice and rats infected either orally with cysts of Pr ugniaud strain or intraperitoneally tip) with tachyzoites of the RH st rain. The animals were killed at regular interval during the acute pha se, and the parasitic burden in mesenteric lymph nodes, spleen, liver, diaphragm, heart, lungs, brain, and blood was assessed by a tissue cu lture method in MRC5 fibroblast cells. Mice infected with the RH strai n showed a drastic increase of the parasitic load in all organs (up to 10(8) parasites /g of organs), and then died. When mice were infected with 50 cysts of Prugniaud strain, parasites were first observed in m esenteric lymph nodes, spleen, and lungs and then in other organs. In rats, infection with 1200 cysts of the same strain led to a similar pa ttern; however, the chronology of the infected organs changed when the y were infected with RH strain tachyzoites. These results suggest that the parasites, present first in the peritoneal cavity in the case of RH ip infection, infect all the adjacent organs and then the blood whi ch disseminates the tachyzoites all over the organism. In contrast, af ter an oral infection, the parasite crosses the intestinal barrier to reach the mesenteric lymph nodes and then the spleen and are finally d istributed by the blood throughout the organism. We also showed that f ollowing infection with a lethal or a sublethal doses of the Prugniaud strain, the parasitic burden in the studied organs was similar and th erefore does not directly correlate with the death of the mice. (C) 19 98 Academic Press.