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Problems have been raised by natural genetic diversity of Trypanosoma cruzi, the causal agent of Chagas' disease, and other protozoa in terms of both basic and applied science. T. cruzi manifests a great diversity of medical and biological properties which could be the origin of clinical variability in the disease. We propose possible correlations between genetic distances, or phylogenetic divergence, and histopathological data. To ascertain this aspect, 15 cloned stocks pertaining to three major clones or genotypes (19, 20 and 39) were compared. Sets of 24 mice infected with each stock were studied for histopathological lesions. Brain, heart, lung, liver, spleen, urinary bladder, bone marrow, colon, kidney and skeletal muscle were extracted from each mouse. Qualitative and quantitative differences showed at histopathological examination. An important encephalic softening was found in brains of most mice infected by genotype 20, corresponding to areas of inflammation and liquified necrosis. Other inflammatory tissue lesions in the histological sections of the three genotypes were similar. Skeletal muscle tropism was higher than cardiac tropism in all the studied genotypes. All three genotypes shared parasite presence in skeletal muscle. Differences related to cardiac tropism were important: in genotype 19, 50% of studied stocks presented pseudocysts; 20% in genotype 20 and 83% in genotype 39. Parasite presence in other tissues was scanty: in brain only in genotype 20 and in spleen and liver only in genotype 39. We found important histopathogenicity differences among the three studied genotypes, but they do not support the hypothesis of zymodeme pathogenic specificity due to the great diversity among stocks within each genotype.

Myocardial damage in Chagas' disease differs, depending on the particular Trypanosoma cruzi stock. It is reasonable to expect that the extent of phylogenetic divergence between lineages will have an impact on the biological properties of the parasite. The aim of the present work was to evaluate this impact on the cardiac damage produced by this protozoan. Heart histopathologic lesions were studied in mice infected with 15 cloned stocks of T. cruzi of various origins pertaining to 3 major clones or genotypes (19, 20, and 39) that share 3 different profiles for a given set of genetic markers. Sets of mice were infected intraperitoneally with 10(6) blood trypomastigotes of each of the T. cruzi clones. The macroscopy study showed a cardiac index (CI) higher than 0.6 (cardiomegaly) in 5 of the 15 stocks studied (33.33%). Inflammatory infiltrates appeared in stocks pertaining to the three genotypes studied without relation to the genetic pattern. Pseudocysts were present at higher levels (83%) in stocks pertaining to genotype 39. A lower rate could be seen in stocks pertaining to genotype 19 (50%). Only one stock pertaining to genotype 20 presented myocardial parasites (20%). Hearts were also studied for lesions in the different cardiac chambers. Inflammatory foci as well as pseudocysts appeared mainly in ventricles, with the left ventricle sharing the highest percentage of pathologic findings. In summary, in spite of the similar inflammatory pattern demonstrated for all stocks studied, the parasite's presence seemed to be related to the genotype of reference, but no relation could be demonstrated with the genetic distances.

We investigated the protective effect of Trypanosoma rangeli against infection with Trypanosoma cruzi in animal models of various ages and with different doses of inoculum. The age of the mice and the dose of parasites determined the course of the infection. When T. cruzi was inoculated into mice after challenge with T. rangeli, parasitaemia was more controlled, mortality decreased and histopathology showed lower inflammatory infiltration and pseudocysts. This study proposes a new murine model of the protective effect of recombinant proteins of T. rangeli for possible application in the vaccines field.

Knowing the great diversity of medical and biological properties of Trypanosoma cruzi, the causal agent of Chagas' disease, we quantified the morphological parameters that typify the different forms of three clones of T. cruzi and their original strain, Bolivia, in comparison among themselves and with strain Bolivia, attempting to provide additional data concerning the clonal biological behaviour of this parasite. Blood forms morphology was quantified using a computerized image analysis (Videoplan/Kontron) and statistical analysis was determined using ANOVA-1 Test. Large number of quantitative differences among slender, broad, and stout forms were found. The comparison of clones I, II and III with their mother strain, leads to the emergence of significant differences in at least 12 parameters out of the 16 we studied. When clones were compared among themselves, the differences decreased. Variations of the percentages of the three kinds of clones were found along the acute infection. These data are the first step in correlating the morphological and pathogenic characteristics of the parasite.

After isolating three clones of Trypanosoma cruzi (Bolivia), we first characterized them according to parasitaemia, pleomorphism and virulence, and then histopathologically. The study's interest lies on the hypothesis that clonal evolution of T. cruzi has a major impact on biologically relevant properties of this parasite. Data obtained from the studies of parasitaemia, pleomorphism and virulence showed no differences between the groups studied. As a final point, the histopathological study shows us a muscular tissue tropism both in clones and in their mother strain (Bolivia). In this paper, we conclude that Bolivia strain and clones isolated from it, pertaining to the same major clone share similar biological properties.

Trypanosoma cruzi, the etiological agent of Chagas' disease, shows a wide variation in its biological behaviour depending on the geographical distribution of different strains. Moreover, some strains can show variations with the course of time. We have studied the tissular tropism of three strains of T. cruzi, Cali, Bolivia and Y, from different geographical origins (Colombia, Bolivia and Brasil respectively) on Swiss mice in order to detect any possible modification in their behaviour attributable only to parasite but not to host variations. The anatomopathological study of sections from heart, brain, liver, spleen, lymphatic ganglion, skeletal muscle and colon from Swiss mice infected with these strains has evidenced the presence of some important discrepancies between the tissular tropism expected from their former descriptions, and classical typification and then observed lesions. The greatest variations were found in the Y strain which had been described as eminently reticulotropic but presented lesions in all the organs except the spleen and lymphatic ganglion. We consider that the variations found in our study can only be explained in terms of changes in the properties of the strains considered, and conclude that the classic typification techniques based on the constancy of the characteristics of the parasite are not fully reliable for the description and clinical management of some evolving strains.

After morphological and histopathological characterization, the Cali strain of T. cruzi isolated from a patient in Cali (Colombia), was also submitted to a morphometrical characterization. For this we estimated 16 cellular parameters in 30 samples of each evolutive form of T. cruzi in blood in NNN medium through planimetry by the IBAS-1 (Image Basic Analytic System). This morphometrical study was completed with a statistical one through the application of the variance (ANOVA-1). This made it possible to evidence a great number of significant differences between the slender, broad and stout forms and also between the short and large epimastigotes from the NNN medium. These data have a real interest for classifying some features of the biological cycle of T. cruzi as well as the future development of diagnosis techniques or therapeutical and prophylactic experiments.

We have carried out a study of the tissular tropism of the strain Y of T. cruzi considering that the different strains of T. cruzi show a great instability in their pathogenic properties with the aim of proving that the classifications of his parasite based in its tissular tropism are not reliable given that these characteristics are subject to change as can be seen by comparing our results with those of other authors. In our study, the Y. strain of T. cruzi shows a strong pancytotropic action, specially with marked cardiotropic aspects. The lack of affectation in the lymphatic ganglion and the small proportion of spleen lesions (8%) as well as the absence of pseudocysts at this level is surprising in a strain which was described as eminently reticulotropic. Our data show that this strain produces cardiac pseudocysts without lesions of the parasitized muscle fiber. The above mentioned data evidence that the biological behavior of a strain and specially its tissular tropism are susceptible to present variations with time.