Histopathology of experimental Chagas disease in NMRI-mice. A long term study following paw infection.

NMRI-mice were infected subcutaneously with T. cruzi Brazil and the pathohistological findings in 17 organs at different times after infection are described. The paw was chosen as injection site, for, due to the great variety of tissues found in a single histological section, the first reactions between host and parasite are best studied here. For this purpose the complete paw was embedded in plastic and sectioned longitudinally. After infection with 5 X 10(4) parasites a shift of parasitism from the initial host cells (macrophages) to the neighbouring muscle cells was observed. This occurred on the 9th day after infection. On the 18th day a generalized parasitism of organs containing muscle had developed, especially of myocardium and alimentary tract. Destruction and inflammation of heart muscle was the most important consequence with respect to mortality. The autonomous nervous system of heart and alimentary tract was involved, although not selectively. Liver and spleen played no role as host tissues. After infection with 10(2) or 10(3) parasites specific alterations in the animals surviving the acute phase were not observed from the 60th to 201st day. A perivenous encephalitis without cerebral parasitism was found in about one half of the experimental animals. It does not correspond to the known 'Chagas encephalitis' and is for the present defined as parainfectious.