MORPHOLOGICAL ASPECTS OF THE MYOCARDITIS AND MYOSITIS IN CALOMYS CALLOSUS EXPERIMENTALLY INFECTED WITH TRYPANOSOMA-CRUZI - FIBROGENESIS ANDSPONTANEOUS REGRESSION OF FIBROSIS

Calomys callosus a wild rodent, is a natural host of Trypanosoma cruzi . Twelve C. callosus were infected with 10(5) trypomastigotes of the F strain (a myotropic strain) of T. cruzi. Parasitemia decreased on the 21st day becoming negative around the 40th day of infection. All anim als survived but had positive parasitological rests, until the end of the experiment The infected animals developed severe inflammation in t he myocardium and skeletal muscle. This process was pronounced from th e 26th to the 30th day and gradually subsided from the 50th day becomi ng absent or residual on the 64th day after infection. Collagen was id entfied by the picro Sirius red method. Fibrogenesis developed early, but regression of fibrosis occurred between the 50th and 64th day. Ult rastructural study disclosed a predominance of macrophages and fibrobl asts in the inflammatory infiltrates, with small numbers of lymphocyte s. Macrophages had active phagocytosis and showed points