Exacerbation of Experimental Trypanosoma cruzi Infection in Mice by Concomitant Malaria*

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Abstract
The effect of malaria on the chronic phase of Chagas'' disease was investigated in mice. The animals were given Plasmodium berghei-infected red blood cells 2-12 mo. after initial inoculation with trypomastigotes of 3 different strains of T. cruzi (Y, CL and Gilmar). In experiments carried out with 1 strain (CL), a somewhat variable but always considerable percentage of mice (average 39%) relapsed into the acute phase of Chagas'' disease. This relapse was characterized by a significant increase in the number of circulating trypomastigotes. Recrudescence was observed with a 2nd strain of T. cruzi (Gilmar), similar in many aspects to the CL strain, e.g., the morphology of blood stages, curve of parasitemia and susceptibility to antibodies in vitro. In mice whose chronic phase was induced by trypomastigotes of the Y strain, malaria infections did not induce a typical acute phase with high parasitemia by T. cruzi. Bloodstream forms of Y parasites differ from those of CL and Gilmar strains morphologically as well as immunologically, i.e., only the Y strain is easily agglutinated and partly inactivated by specific immune serum. In light of this and other known characteristics of the strains used, mechanisms which allow malaria infections selectively to suppress acquired host resistance to certain strains of T. cruzi are postulated.