Trypanosoma cruzi: impact of clonal evolution of the parasite on its biological and medical properties

Analyses of 32 loci clarify phylogenetic relationships among Trypanosoma cruzi lineages and support a single hybridization prior to human contact

Background

The genetic diversity of Trypanosoma cruzi, the etiological agent of Chagas disease, has been traditionally divided in two major groups, T. cruzi I and II, corresponding to discrete typing units TcI and TcII-VI under a recently proposed nomenclature. The two major groups of T. cruzi seem to differ in important biological characteristics, and are thus thought to represent a natural division relevant for epidemiological studies and development of prophylaxis. To understand the potential connection between the different manifestations of Chagas disease and variability of T. cruzi strains, it is essential to have a correct reconstruction of the evolutionary history of T. cruzi.

Methodology/Principal Findings

Nucleotide sequences from 32 unlinked loci (>26 Kilobases of aligned sequence) were used to reconstruct the evolutionary history of strains representing the known genetic variability of T. cruzi. Thorough phylogenetic analyses show that the original classification of T. cruzi in two major lineages does not reflect its evolutionary history and that there is only strong evidence for one major and recent hybridization event in the history of this species. Furthermore, estimates of divergence times using Bayesian methods show that current extant lineages of T. cruzi diverged very recently, within the last 3 million years, and that the major hybridization event leading to hybrid lineages TcV and TcVI occurred less than 1 million years ago, well before the contact of T. cruzi with humans in South America.

Conclusions/Significance

The described phylogenetic relationships among the six major genetic subdivisions of T. cruzi should serve as guidelines for targeted epidemiological and prophylaxis studies. We suggest that it is important to reconsider conclusions from previous studies that have attempted to uncover important biological differences between the two originally defined major lineages of T. cruzi especially if those conclusions were obtained from single or few strains.

Trypanosoma cruzi is the protozoan parasite that causes Chagas disease, a major health problem in Latin America. The genetic diversity of this parasite has been traditionally divided in two major groups: T. cruzi I and II, which can be further divided in six major genetic subdivisions (subgroups TcI-TcVI). T. cruzi I and II seem to differ in important biological characteristics, and are thought to represent a natural division relevant for epidemiological studies and development of prophylaxis. Having a correct reconstruction of the evolutionary history of T. cruzi is essential for understanding the potential connection between the genetic and phenotypic variability of T. cruzi with the different manifestations of Chagas disease. Here we present results from a comprehensive phylogenetic analysis of T. cruzi using more than 26 Kb of aligned sequence data. We show strong evidence that T. cruzi II (TcII-VI) is not a natural evolutionary group but a paraphyletic lineage and that all major lineages of T. cruzi evolved recently (<3 million years ago [mya]). Furthermore, the sequence data is consistent with one major hybridization event having occurred in this species recently (< 1 mya) but well before T. cruzi entered in contact with humans in South America.

The Trypanosoma cruzi genome; conserved core genes and extremely variable surface molecule families

The protozoan parasite Trypanosoma cruzi is an important but neglected pathogen that causes chagas disease, which affects millions of people, mainly in latin America. The population structure and epidemiology of the parasite are complex, with much variability among strains. The genome sequence of a reference strain, CL Brener, was published in 2005, and the availability of this sequence has both revealed the complexity of the parasite genome and greatly facilitated research into parasite biology and pathogenesis, by making the sequences of more than 8000 core genes available. The T. cruzi genome is highly repetitive, which has resulted in inaccuracies in the genome sequence, and attempts have been made to provide a deeper analysis of repeated genes as a complement to the genome sequence. The genome was found to be organized in stable core regions containing housekeeping and other genes, surrounded by highly repetitive, often sub-telomeric highly variable regions containing multiple members of large families of surface molecule genes. Comparative sequencing of T. cruzi strains has been initiated and the results show that the core gene content of the parasite is highly conserved, but that much sequence variability, 3-4% difference at the DNA level on average between strains in coding regions, is present. The additional genomes will improve the understanding of parasite biology and epidemiology.

Shotgun sequencing analysis of Trypanosoma cruzi I Sylvio X10/1 and comparison with T. cruzi VI CL Brener

Trypanosoma cruzi is the causative agent of Chagas disease, which affects more than 9 million people in Latin America. We have generated a draft genome sequence of the TcI strain Sylvio X10/1 and compared it to the TcVI reference strain CL Brener to identify lineage-specific features. We found virtually no differences in the core gene content of CL Brener and Sylvio X10/1 by presence/absence analysis, but 6 open reading frames from CL Brener were missing in Sylvio X10/1. Several multicopy gene families, including DGF, mucin, MASP and GP63 were found to contain substantially fewer genes in Sylvio X10/1, based on sequence read estimations. 1,861 small insertion-deletion events and 77,349 nucleotide differences, 23% of which were non-synonymous and associated with radical amino acid changes, further distinguish these two genomes. There were 336 genes indicated as under positive selection, 145 unique to T. cruzi in comparison to T. brucei and Leishmania. This study provides a framework for further comparative analyses of two major T. cruzi lineages and also highlights the need for sequencing more strains to understand fully the genomic composition of this parasite.

Chagas disease is a major health problem in Latin America and it is caused by the protozoan parasite Trypanosoma cruzi. The genome sequence of the T. cruzi strain CL Brener (TcVI) has revealed a genome with large repertoires of genes for surface antigens, among other features. In the present study, we sequenced the genome of a representative member of TcI, the predominant agent of Chagas disease North of the Amazon and performed comparative analyses with CL Brener. Genetic variation between strains can potentially explain differences in disease pathogenesis, host preferences and aid the identification of drug targets. Our analysis showed that the two genomes have very similar sets of genes, but contain large differences in the relative size of several important gene families. Moreover, an abundance of allelic sequence variation was found in a large fraction of genes, and an evolutionary analysis indicated that many genes have evolved at different rates.

Immunological identification of Trypanosoma cruzi lineages in human infection along the endemic area

Genotyping studies show a polarized geographic distribution of Trypanosoma cruzi lineages in humans. Here, we assessed their distribution along Latin America through an immunological approach we designated Western blot (WB) assay with Trypomastigote small-surface antigen (TSSA) I and TSSA II (TSSA-WB). These antigens are expressed by T. cruzi I (TCI; now TcI) and T. cruzi II (TCII; reclassified as TcII to TcVI) parasites. TSSA-WB showed good concordance with genotyping tests. An unexpected frequency of TSSA II recognition was observed in Colombia, Venezuela, and Mexico (northern region of Latin America). In Argentina and Paraguay (southern region), immunophenotyping confirmed the already reported TCII (TcII to TcVI) dominance. The lineage distribution between these regions showed significant difference but not among countries within them (except for Colombia and Venezuela). TSSA-WB shows TCII emergence in the northern region where TCI was reported as dominant or even as the unique T. cruzi lineage infecting humans.

Phylogenetic character mapping of proteomic diversity shows high correlation with subspecific phylogenetic diversity in Trypanosoma cruzi

We performed a phylogenetic character mapping on 26 stocks of Trypanosoma cruzi, the parasite responsible for Chagas disease, and 2 stocks of the sister taxon T. cruzi marinkellei to test for possible associations between T. cruzi-subspecific phylogenetic diversity and levels of protein expression, as examined by proteomic analysis and mass spectrometry. We observed a high level of correlation (P < 10(-4)) between genetic distance, as established by multilocus enzyme electrophoresis, and proteomic dissimilarities estimated by proteomic Euclidian distances. Several proteins were found to be specifically associated to T. cruzi phylogenetic subdivisions (discrete typing units). This study explores the previously uncharacterized links between infraspecific phylogenetic diversity and gene expression in a human pathogen. It opens the way to searching for new vaccine and drug targets and for identification of specific biomarkers at the subspecific level of pathogens.

Biological characterization of Trypanosoma cruzi stocks from domestic and sylvatic vectors in Sierra Nevada of Santa Marta, Colombia

Sierra Nevada of Santa Marta is one of the most endemic regions of Chagas disease in Colombia. In this study, we compared the biological behavior and genetic features of Trypanosoma cruzi stocks that were isolated from domestic and sylvatic insects in this area. Rhodnius prolixus (from domestic environments) and Triatoma dimidiata (from sylvatic, peridomestic and domestic environments) are the most important vectors in this region. Genetic characterization showed that all stocks corresponded to T. cruzi I, but LSSP-PCR analyses indicated that some genotypes were present in both environments. Biological characterization in vitro showed a low growth rate in sylvatic T. cruzi stocks and in some domestic T. cruzi stocks, possibly indicating the presence of stocks with similar behavior in both transmission cycles. In parallel, in vivo behavioral analysis also indicated that T. cruzi stocks are variable and this species did not show a correlation between the environments where they were isolated. In addition, all stocks demonstrated a low mortality rate and histopathological lesions in heart, skeletal muscle and colon tissue. Moreover, our data indicated that experimentally infected chagasic mice displayed a relation between their myocardial inflammation intensity, parasitism tissue and parasite load using the qPCR. In conclusion, our results indicate that the T. cruzi stocks present in SNSM have similar biological behavior and do not show a correlation with the different transmission cycles. This could be explained by the complex transmission dynamics of T. cruzi in Sierra Nevada of Santa Marta, where hosts, vectors (e.g., T. dimidiata) and reservoirs circulate in both environments due to the close contact between the two transmission cycles, favoring environment overlapping. This knowledge is an important key to understanding the epidemiology and pathology of Chagas disease in this Colombian region. Furthermore, our findings could be of significant use in the design of control strategies restricted to a specified endemic region.

Usefulness of the polymerase chain reaction for monitoring cure of mice infected with different Trypanosoma cruzi clonal genotypes following treatment with benznidazole

The capacity of the polymerase chain reaction (PCR) to detect the DNA of Trypanosoma cruzi was evaluated in 90 blood samples from BALB/c mice infected with T. cruzi cloned stocks of genotypes 19 and 20 (T. cruzi I) and 39 and 32 (T. cruzi II), and treated with benznidazole. The results from the fresh blood examination, hemoculture, and ELISA allowed to group the treated animals into: cured (TC), dissociated (DIS) and non-cured (NC). The PCR detected T. cruzi DNA in 50.9%, 58.3% and 100.0% of the samples from TC, DIS and NC mice, respectively. These DNA possibly derives from live T. cruzi or from recently lysed parasites, suggests that these animals are in fact not cured. The difference between the PCR results and results obtained using other techniques was statistically significant and independent of the parasite genotype. The PCR described has therefore potential to be used in cure control of treated patients.

Implications of genetic variability of Trypanosoma cruzi for the pathogenesis of Chagas disease

Trypanosoma cruzi, the etiological agent of Chagas disease, presents a high degree of intraspecific genetic variability, with possible implications for the clinical forms of the disease, like the development of cardiopathy, megaesophagus, and megacolon, alone or in combination. This tissue tropism involved in the pathogenesis of Chagas disease has still not been totally elucidated. Thus, the current review approaches key aspects of T. cruzi genetic diversity, the clinical forms of Chagas disease, and the infection of the host cell by the parasite and the immune response. Other aspects discussed here include the release of immunosuppressive factors by the parasite, acting in the host's immune response pathways; host cell apoptosis inhibition; the pathogenesis of chagasic megaesophagus, which can be related to host-parasite interaction; and finally the association between megaesophagus and increased risk for the development of squamous-cell esophageal carcinoma. However, despite great advances in the understanding of this disease, it is still not possible to establish the true relationship between the parasite's genetic variability and the clinical form of Chagas disease.

Trypanosoma cruzi: Subtractive hybridization as a molecular strategy to generate new targets to distinguish groups and hybrids

RAPD analysis and sequences of the mini-exon and ribosomal genes show that Trypanosoma cruzi can be clustered into two phylogenetic groups-T. cruzi I and II. Herein, the Representational Difference Analysis (RDA) method was used, providing new targets specific for each group. After three rounds of RDA hybridizing F strain (tester) with Y strain (driver) and vice-versa, an F-specific (F#30) and Y-specific (Y#22) clone were obtained specifically recognizing isolates from Amazonas (T. cruzi I) and Piauí (T. cruzi II). These segments corresponded to an unspecified protein (F#30) and a trans-sialidase (Y#22). Analysis of the F#30 sequence in T. cruzi I, T. cruzi II and zymodeme 3 samples displayed negligible specific differences that distinguished each group. In addition this F#30 gene has great potential as a hybrid marker.

Sequence diversity and differential expression of Tc52 immuno-regulatory protein in Trypanosoma cruzi: potential implications in the biological variability of strains

Trypanosoma cruzi is highly heterogeneous in terms of genetics and biological properties. To explore the diversity of T. cruzi, we focused our study on the T. cruzi Tc52 protein playing a critical immunosuppressive role during infection. Sequence variability and expression levels of this virulence factor were analysed in various strains. Among the 40 amino acid substitutions detected in the Tc52 coding sequences, three substitutions may have an impact on protein activity or function, as two are localized in sites involved in the glutathione binding and the third is present in the region bearing immunomodulatory function. This sequence variability was consistent with the genetic subdivisions of T. cruzi. Moreover, we observed that the level of Tc52 transcripts and proteins varied between the different strains, but we did not find a significant correlation between Tc52 expression and the phylogeny of the parasite. Thus, both diversity in the sequences and differences in the expression levels of Tc52 protein may be involved in the biological variability of T. cruzi, especially in virulence and immunosuppression properties of T. cruzi strains.

Impact of dual infections on chemotherapeutic efficacy in BALB/c mice infected with major genotypes of Trypanosoma cruzi

The aim of this work was to investigate the impact of dual infections with stocks of Trypanosoma cruzi major genotypes on benznidazole (BZ) treatment efficacy. For this purpose, T. cruzi stocks representative of the genetic T. cruzi lineages, displaying different susceptibilities to BZ, belonging to the major T. cruzi genotypes broadly dispersed in North and South America and important in Chagas' disease epidemiology were used. Therapeutic efficacy was observed in 27.8% of the animals treated. Following BZ susceptibility classification, significant differences were observed in dual infections on the major genotype level, demonstrating that combinations of genotypes 19+39 and genotypes 19+32 led to a shift in the expected BZ susceptibility profile toward the resistance pattern. Analysis on the T. cruzi stock level demonstrated that 9 out of 24 dual infections shifted the expected BZ susceptibility profile compared with the respective single infections, including shifts toward lower and higher BZ susceptibilities. Microsatellite identification was able to identify a mixture of T. cruzi stocks in 7.7% of the T. cruzi isolates from infected and untreated mice (6.9%) and infected and treated but not cured mice (9.0%), revealing in some mixtures of BZ-susceptible and -resistant stocks that the T. cruzi stock identified after BZ treatment was previously susceptible in single infections. Considering the clonal structure and evolution of T. cruzi, an unexpected result was the identification of parasite subpopulations with distinct microsatellite alleles in relation to the original stocks observed in 12.2% of the isolates. Taken together, the data suggest that mixed infections, already verified in nature, may have an important impact on the efficacy of chemotherapy.

Clinical forms of Trypanosoma cruzi infected individuals in the chronic phase of Chagas disease in Puebla, Mexico

In Mexico, despite the relatively high seroprevalence of Trypanosoma cruzi infection in humans in some areas, reported morbidity of Chagas disease is not clear. We determined clinical stage in 71 individuals seropositive to T. cruzi in the state of Puebla, Mexico, an area endemic for Chagas disease with a reported seroprevalence of 7.7%. Diagnosis of Chagas disease was made by two standardized serological tests (ELISA, IHA). Individuals were stratified according to clinical studies. All patients were submitted to EKG, barium swallow, and barium enema. Groups were identified as indeterminate form (IF) asymptomatic individuals without evidence of abnormalities (n = 34 cases); those with gastrointestinal alterations (12 patients) including symptoms of abnormal relaxation of the lower esophageal sphincter and absent peristalsis in the esophageal body, grade I megaesophagus, and/or megacolon; patients with clinical manifestations and documented changes of chronic Chagas heart disease who were subdivided as follows: mild (8 patients)--mild electrocardiographic changes of ventricular repolarization, sinus bradychardia); moderate (6 patients)--left bundle branch block, right bundle branch block associated with left anterior fascicular block); severe (8 patients)--signs of cardiomegaly, dilated cardiomyopathy); and the associated form (3 cases) that included presence of both cardiomyopathy and megaesophagus. These data highlight the importance of accurate evaluation of the prevalence and clinical course of Chagas disease in endemic and non-endemic areas of Mexico.

Efficacy and mechanisms of alpha-solasonine-and alpha-solamargine-induced cytolysis on two strains of Trypanosoma cruzi

Two genetically diverse strains of Trypanosoma cruzi were tested in vitro for susceptibility to the solanum-derived triglycoside alkaloids solasonine and solamargine. Cytolytic assays were performed on epimastigotes (EMs) and bloodstream form trypomastigotes (BSFs) lifecycle stages by using serial dilutions of each alkaloid. Each alkaloid effectively lysed both lifecycle stages, although solasonine routinely required higher concentrations to induce similar results. EMs demonstrated greater resistance to cytolysis than BSFs at equal concentrations of either alkaloid. No significant resistance could be correlated to parasite strain. The reported synergistic cytolytic effects observed upon compounding solasonine and solamargine together were also tested. We failed to identify any cytolytic synergism in cultures of EMs or BSFs. The role of rhamnose-binding proteins (RBPs) in mediating cytolysis was investigated through competitive inhibition experiments. The addition of exogenous L: -rhamnose to the media failed to reduce parasite attrition independent of the parasite lifecycle stage. Based on these results, we suggest the mechanisms involved in cytolysis of T. cruzi by solasonine and solamargine are largely independent of rhamnose receptor-specific interactions. We propose that attrition likely involves less-specific carbohydrate interactions, which lead to the formation and intercalation of sterol complexes into the parasite plasma membrane.

Schizodeme analysis of Trypanosoma cruzi Colombian strain clones isolated from the acute phase of murine infection

Colombian strain of Trypanosoma cruzi, biodeme Type III (T. cruzi I), has been cloned by micromanipulation at two phases of the acute infection: early (10 days ) and advanced (30 days). Twelve clones were obtained therefrom. Characterization by their biological and biochemical behavior showed an identity among the several clones and their parental strain, albeit with different degrees of virulence. Molecular characterization of the kinetoplast DNA (kDNA) after amplification by polymerase chain reaction revealed identical profiles of the bands from the kDNA minicircle by the analysis of restriction fragment length polymorphism for the isolated clones, their parental strain, and to the clones isolated at two different phases of the infection. Results suggest the predominance of a "principal clone", in the composition of the Colombian strain, responsible for the biological and biochemical behavior. However, no relationship was detected between the molecular profile of kDNA and the degree of virulence presented by the several clones.

Trypanosoma cruzi strains isolated from human, vector, and animal reservoir in the same endemic region in Mexico and typed as T. cruzi I, discrete typing unit 1 exhibit considerable biological diversity

In this study, three strains of Trypanosoma cruzi were isolated at the same time and in the same endemic region in Mexico from a human patient with chronic chagasic cardiomyopathy (RyC-H); vector (Triatoma barberi) (RyC-V); and rodent reservoir (Peromyscus peromyscus) (RyC-R). The three strains were characterized by multilocus enzyme electrophoresis, random amplified polymorphic DNA, and by pathological profiles in experimental animals (biodemes). Based on the analysis of genetic markers the three parasite strains were typed as belonging to T. cruzi I major group, discrete typing unit 1. The pathological profile of RyC-H and RyC-V strains indicated medium virulence and low mortality and, accordingly, the strains should be considered as belonging to biodeme Type III. On the other hand, the parasites from RyC-R strain induced more severe inflammatory processes and high mortality (> 40%) and were considered as belonging to biodeme Type II. The relationship between genotypes and biological characteristics in T. cruzi strains is still debated and not clearly understood. An expert committee recommended in 1999 that Biodeme Type III would correspond to T. cruzi I group, whereas Biodeme Type II, to T. cruzi II group. Our findings suggest that, at least for Mexican isolates, this correlation does not stand and that biological characteristics such as pathogenicity and virulence could be determined by factors different from those identified in the genotypic characterization.

Trypanosoma cruzi: Sensitivity of the polymerase chain reaction for detecting the parasite in the blood of mice infected with different clonal genotypes

The polymerase chain reaction showed high sensitivity for detecting Trypanosoma cruzi in the blood of mice, independent of clonal genotype (19, 20-T. cruzi I; 32, 39-T. cruzi II) or phase of the infection (acute or chronic).

Infectivity for mice of Trypanosoma cruzi I and II strains isolated from different hosts

In this paper, the infectivity for mice of Trypanosoma cruzi I and II strains isolated from sylvatic animals, triatomines, and humans is determined using fresh blood examination, hemoculture, culture of macerated organs, and polymerase chain reaction (PCR). Six strains were considered to have low infectivity (9.1-18.2%), five medium (27.3-45.4%), and one high (100.0%). Infectivity of T. cruzi strains isolated from sylvatic animals was significantly higher than that of strains isolated from humans and triatomines (p=0.0141). No significant difference was observed between the infectivity of T. cruzi I and II strains. The parasite was detected by fresh blood examination in one strain, by hemoculture and culture of macerated organs in four strains, and by PCR in all strains. We conclude that the infectivity is related to the host from which the strains were isolated, but the infectivity is not related to the genetic group of the parasite. We also conclude that the majority of the strains studied have low and medium infectivity for mice, and that PCR is an important tool to detect T. cruzi in strains with this biological characteristic.

Trypanosoma cruzi: Impact of dual-clone infections on parasite biological properties in BALB/c mice

Herein, we have analyzed major biological properties following dual-clone Trypanosoma cruzi infections in BALB/c mice. Eight T. cruzi clonal stocks, two of each principal genotype, including genotype 19 and 20 (T. cruzi I), hybrid genotype 39 (T. cruzi) and 32 (T. cruzi II) were combined into 24 different dual-clone infections. Special attention was given to characterize biological parameters assayed including: prepatent period, patent period, maximum of parasitemia, day of maximum parasitemia, area under the parasitemia curve, infectivity, mortality, and hemoculture positivity. Our findings clearly demonstrated that features resultant of dual-clone infections of T. cruzi clonal stocks did not display either the characteristics of the corresponding monoclonal infections or the theoretical mixture based on the respective monoclonal infections. Significant changes in the expected values were observed in 4.2-79.2% of the mixtures considering the eight biological parameters studied. A lower frequency of significant differences was found for mixtures composed by phylogenetically distant clonal stocks. Altogether, our data support our hypothesis that mixed T. cruzi infections have a great impact on the biological properties of the parasite in the host and re-emphasizes the importance of considering the possible occurrence of natural mixed infections in humans and their consequences on the biological aspects of ongoing Chagas' disease.

Trypanosoma cruzi: Sequence polymorphism of the gene encoding the Tc52 immunoregulatory-released factor in relation to the phylogenetic diversity of the species

We have previously identified a Trypanosoma cruzi gene encoding a protein named Tc52 sharing structural and functional properties with the thioredoxin and glutaredoxin family involved in thiol-disulfide redox reactions. Gene targeting strategy and immunological studies allowed showing that Tc52 is among T. cruzi virulence factors. Taking into account that T. cruzi has a genetic variability that might be important determinant that governs the different behaviour of T. cruzi clones in vitro and in vivo, we thought it was of interest to analyse the sequence polymorphism of Tc52 gene in several reference clones. The DNA sequences of 12 clones which represent the whole genetic diversity of T. cruzi allowed showing that 40 amino-acid positions over 400 analysed are targets for mutations. A number of residues corresponding to putative amino-acids playing a role in GSH binding and/or enzymatic function and others located nearby are subject to mutations. Although the immunological analysis showed that Tc52 is present in parasite extracts from different clones, it is possible that the amino-acid differences could affect the enzymatic and/or the immunomodulatory function of Tc52 variants and therefore the parasite phenotype.

Changes in the cardiac beta-adrenergic system provoked by different T. cruzi strains

BACKGROUND

It has been demonstrated that the beta-adrenergic signal transduction system is altered somewhere along its pathway in Trypanosoma cruzi infected hearts and we think that these alterations would differ according to the infection phase and the parasite strain. Their study would be important for the understanding of the disease's pathophysiology.

METHODS

In the present work we studied important components of this system in mice hearts infected with T. cruzi, Tulahuen strain and with SGO-Z12 isolate, obtained from a patient of an endemic area, in the acute phase of the infection, determining: the plasma catecholamines levels, the beta-receptors density and affinity as well as their function, the cardiac concentration of cAMP and the cardiac contractility as the physiologic response to the initial stimulus.

RESULTS

Plasma catecholamines levels were diminished in both infected groups when compared to the uninfected one (P < 0.01). The receptor's affinity was also diminished (P < 0.05) while their density was augmented only in the SGO-Z12 infected one (P < 0.01). The cAMP levels were higher in both infected groups (P < 0.01), the basal contractile force however increased only in the Tulahuen infected one (P < 0.01) while the response to catecholamines remained unchanged. The hearts infected with the SGO Z12 isolate presented an inferior response to epinephrine (P < 0.05) than the ventricles infected with the Tulahuen strain.

CONCLUSIONS

This model represents an important approach to understand the biochemical, physiological and molecular changes in the cardiac beta-adrenergic signalling that clearly begin in the acute phase of Chagas' disease and reveal a clear differentiation in the alterations produced by different parasite strains.

Trypanosoma cruzi: Chemotherapeutic effects of clomipramine in mice infected with an isolate obtained from an endemic area

The susceptibility of Trypanosoma cruzi strains to nifurtimox and benznidazole has been investigated and resistant strains have been described. Some tricyclic drugs are lethal for trypomastigote and epimastigote forms of T. cruzi (Tulahuen strain) and prevent the disease in mice. We investigated whether clomipramine, a tricyclic antidepressant drug with anti-trypanothione reductase and anti-calmodulin effects, could be effective in treating Albino Swiss mice infected with trypomastigotes of a new T. cruzi isolate from a chronic patient from an endemic area of Argentina in two different treatment schedules. Both treatment schedules were effective in reducing electrocardiographic changes and preventing myocardial structural damage. The cardiac beta-receptors low affinity was compensated for by an increment in their density. This probably maintained cardiac function since 70% of the mice survived for more than 2 years even though anti-cruzipain titers remained high. These results demonstrate that clomipramine, clinically used as a neuroleptic, could be a promising trypanocidal agent for the treatment of Chagas' disease.

Differential gene expression in benznidazole-resistant Trypanosoma cruzi parasites

We analyzed the differential gene expression among representative Trypanosoma cruzi stocks in relation to benznidazole exposures using a random differentially expressed sequences (RADES) technique. Studies were carried out with drug pressure both at the natural susceptibility level of the wild-type parasite (50% inhibitory concentration for the wild type) and at different resistance levels. The pattern of differential gene expression performed with resistant stocks was compared to the population structure of this parasite, established by random amplified polymorphic DNA analysis and multilocus enzyme electrophoresis. A RADES band polymorphism was observed, and over- or underexpression was linked to the resistance level of the stock. The analysis of RADES bands suggested that different products may be involved in benznidazole resistance mechanisms. No significant association was found between phylogenetic clustering and benznidazole susceptibility. Benznidazole resistance may involve several mechanisms, depending on the level of drug exposure.

Influence of the long-term Trypanosoma cruzi infection in vertebrate host on the genetic and biological diversity of the parasite

The influence of the long-term Trypanosoma cruzi infection in vertebrate host on the biological and genetic properties of the parasite was evaluated. Four T. cruzi isolates obtained from different chronic chagasic dogs infected with Berenice-78 T. cruzi strain during 2 and 7 years were comparatively analyzed. The long-term T. cruzi infection has led to alterations in parasitemia, virulence and pathogenicity of Be-78 strain for mice. These biological parameters varied from low to high in realation to the parental strain. Randomly amplified polymorphic DNA and isoenzyme profiles detected two distinct genetic groups of parasites. The first group included the parental strain and two T. cruzi isolates, and the second group the two other isolates. Interestingly, the isolates of the second group showed a reversibility of the genetic profile to the parental strain after 25 passages in mice. No correlation between the genetic groups and biological properties of the isolates was observed. Our findings confirmed the population heterogeneity of the Be-78 strain, and showed how differently it responds to the long-term infection in the same vertebrate hosts.

Response to chemotherapy with benznidazole of clones isolated from the 21SF strain of Trypanosoma cruzi (biodeme Type II, Trypanosoma cruzi II)

Susceptibility to chemotherapy with benznidazole was investigated of 5 clones isolated from the 21 SF strain (biodeme Type II, Trypanosoma cruzi II). Swiss mice were infected with the parental strain for each clone and submitted to chemotherapy with benznidazole (100mg/kg/day during 90 days). Treatment determined negativity of the parasitemia. Cure rates were evaluated by parasitological cure tests. Serology was evaluated for treated animals (titers from negative to 1:640) and untreated controls (1:160 to 1:640). Cure rates varied from 30 to 100% for the 5 clones, and were 25% for the parental strain. Results suggested that the variability of response to treatment of the clonal populations of Trypanosoma cruzi II strains is responsible for the high variation in the response to chemotherapy with benznidazole and nifurtimox by strains of this biodeme.

Differential infectivity and immunopathology in murine experimental infections by two natural clones belonging to theTrypanosoma cruziI lineage

Immunopathology of Chagas' disease in Balb/c mice infected with 2Trypanosoma cruziclones, belonging to theT. cruziI lineage and presenting differentin vitrovirulence (P/209 cl1>SO34 cl4) was compared. In the acute phase, evading mechanisms such as parasite-induced lymphocyte polyclonal activation and T cell immunosuppression were higher in mice infected with the clone giving a higher parasitaemia (P/209 cl1). A similar increase of non-specific isotypes was observed in both infections with IgG2a prevalence. Interestingly, CD8+ cell hypercellularity and lymphocyte immunosuppression were observed during the chronic phase (245 days post-infection) in mice infected by the most virulent clone. In the same way, the parasite-specific antibody response was more intense in P/209 cl1-infected mice over the acute phase. During the chronic phase this response remarkably dropped down in SO34 cl4-infected mice exclusively. Finally, P/209 cl1-infected mice presented a more severe inflammation and tissue damage in heart and quadriceps than SO34 cl4-infected mice. This comparative study showed differences between the two clones: a higher virulencein vivobeing clearly associated with a greater ability to induce evasion mechanisms and severe tissue damage.

Intra-strain clonal phenotypic variation of Tritrichomonas foetus is related to the cytotoxicity exerted by the parasite to cultured cells

As observed in most of the investigated trichomonads, a strain of Tritrichomonas foetus includes different parasite subpopulations. Such population diversity might account for important properties such as the ability of the parasite to destroy host cells. The aim of this study was to characterize the cytotoxicity exerted by subpopulations (named as K1, K2, K3, K4 and K5) of an isolate of T. foetus on epithelial cultured cells. The five populations studied here destroyed epithelial monolayers at different rates (from 25% to 55%), even though the cytoadhesion level and whole-cell protease activity were closely related among them. We were also able to detect differences in contact-dependent and contact-independent cytotoxicity mechanisms among the five populations. An extracellular parasite protease had varying activity among the parasite populations. The intensity of contact-independent cytotoxicity was strictly related to the degree of enzyme activation, suggesting that such a protease might be involved in the cytotoxicity mediated by T. foetus.

Lack of correlation between in vitro susceptibility to Benznidazole and phylogenetic diversity of Trypanosoma cruzi, the agent of Chagas disease

Chagas disease remains an important health problem in Central and South America. Nitroimidazole derivative drugs like Benznidazole are commonly used to treat Trypanosoma cruzi infection. Natural variation of drug susceptibility between various T. cruzi stocks has been proposed as a possible explanation of treatment failure. Thus, the aim of this work was to determine potential correlations between in vitro Benznidazole susceptibility of different T. cruzi stocks and their genetic diversity. For this purpose, 16 natural stocks representing the overall genetic diversity of the parasite were analysed. Genetic characterisation was assessed by both random amplified polymorphic DNA (RAPD) and multilocus enzyme electrophoresis (MLEE) analyses. Drug activity was determined by two complementary methods, the MTT-PMS micro-method and FACs analysis. The 50% inhibitory concentrations (IC(50)s) were determined. Important variation of IC(50) values (7.3-16.9 microM) among stocks belonging to different discrete typing units (DTUs) was recorded. Further, correlation analysis showed that natural susceptibility to Benznidazole in T. cruzi expressed as IC(50) level was not related with its genetic structure represented by the different DTUs. These results are discussed in relation with the proposed hypothesis establishing a link between genetic diversity and biological behaviour in T. cruzi.

Leishmania (Viannia): genetic analysis of cutaneous and mucosal strains isolated from the same patient

Ten pairs of Leishmania (Viannia) strains isolated from mucosal and cutaneous lesions of the same patient were analyzed genotypically in order to determine whether populations that had metastasized to mucosal sites differed from those in the cutaneous lesion. The strains were previously characterized by multi locus enzyme electrophoresis and/or monoclonal antibodies reactivity, and, for this study, only isolates from the same patient which were identified as the same species were employed. PCR-RFLP of internal transcribed spacer (ITS) rDNA, random amplified polymorphic DNA (RAPD), and schizodeme analyses were conducted. All genotyping methods revealed microheterogeneity between cutaneous and mucosal isolates from the same patient. The PCR-RFLP of the ITS rDNA and RAPD analysis were numerically analyzed through similarity coefficients and dendrograms were generated. All phenograms clustered cutaneous and mucosal strains of the same patient in one branch with a high degree of similarity, and phenetic analysis matched between them. Schizodeme analysis revealed differences between strains that composed some pairs. Genetic analyses indicate that some populations that metastasize to mucosal sites are distinguishable from the population in cutaneous lesions, however, other approaches will be required to associate genetic polymorphisms with the cutaneous or mucosal phenotype of strains.

Trypanosoma cruzi: long-term sub-cultures in two different culture media do not confirm the existence of highly versatile multilocus genotypes

Trypanosoma cruzi Y reference strain is found in many laboratories under at least two highly distinct genotypes, A and B corresponding to the 'discrete typing units' T. cruzi IIb and T. cruzi IId, respectively. Previous work has reported reversible switches between these genotypes according to the culture media used in the experiments: genotype A would be associated with blood-enriched culture media, while genotype B would be associated with blood-free culture media. We tried to reproduce this observation, but used a different cloning method of individual organisms. Our cloning was verified visually under the microscope, while the previous studies relied on a cloning by dilution only. The subclones so obtained were submitted to long-term exposure to both media, and no change was observed in isoenzyme and random amplified polymorphic DNA genotypes. The discrepancy is probably explained by the cloning method: clones obtained from the previous method (dilution and plating) could come from several parasite cells while only one cell generates a clone when micro-manipulation is used.

Genetic subdivisions within Trypanosoma cruzi (Discrete Typing Units) and their relevance for molecular epidemiology and experimental evolution

Background

This paper summarizes the main results obtained on Trypanosoma cruzi genetic diversity and population structure since this parasite became the theme of many genetic and molecular studies in the early seventies.

Results

T. cruzi exibits a paradigmatic pattern of long-term, clonal evolution, which has structured its natural populations into several discrete genetic subdivisions or "Discrete Typing Units" (DTU). Rare hybridization events are nevertheless detectable in natural populations and have been recently obtained in the laboratory.

Conclusions

The DTUs and natural clones of T. cruzi constitute relevant units for molecular epidemiology and experimental evolution. Experimental mating opens the way to an in-depth knowledge of this parasite's formal genetics.

Trypanosoma cruzi: genetic group with peculiar biochemical and biological behavior

Thirty-two Trypanosoma cruzi strains, isolated from chronic chagasic patients in the northwest of the state of Paran (Brazil), were analyzed using molecular, biochemical and biological characteristics. Genotypic analysis using randomly amplified polymorphic DNA and simple sequence repeat-anchored polymerase chain reaction amplified profiles showed a large, genetically well-correlated group that contained the majority of the strains and a divergent group that included the PR-150 strain. For glycoconjugate composition, the PR-150 strain was different from the other strains considering the absence or presence of specific bands in aqueous or detergent phases. This strain was also totally different from the others in one out of the six parameters related to in vitro and in vivo biological behavior. We highlight the fact that the PR-150 was totally resistant to benznidazole. For the other biological parameters this strain was not totally distinct from the others, but it showed a peculiar behavior.

Evidence for genetic exchange and hybridization in Trypanosoma cruzi based on nucleotide sequences and molecular karyotype

Trypanosoma cruzi is thought to undergo predominant clonal evolution, as determined by population genetics studies. However, this model does not exclude occasional recombination, which existence is strongly suggested by several recent studies. We sequenced a portion of the maxicircle cytochrome b (CYb) gene and of the nuclear rRNA promoter region from representative strains of six T. cruzi genetic lineages isolated from anthroponotic environments and man (lineages IIb, IId and IIe), sylvatic environments (lineages IIa and IIc) or both (lineage I). Phylogenetic analyses based on the two genes were incongruent. Remarkably, in lineage IIe, CYb and rRNA sequences were very closely related to those of lineages IIc and IIb, respectively. One stock of lineage IId showed rRNA sequence heterogeneity, with both IIb-like and IIc-like copies. Analysis of the size variation of six distinct pairs of putative homologous chromosomes revealed a bimodal distribution of chromosomal sizes across T. cruzi. Notably, stocks of lineages IId and IIe had several chromosomal pairs distributed in distinct modes, with the corresponding modes individually found in lineages IIb and IIc. Together, these data indicate the origin of lineages IId and IIe by hybridization between representatives of lineages IIb and IIc. CYb and rRNA sequences clustered into three and four major lineages, respectively. Data were in agreement with the distinction of six genetic lineages, but not with their proposed grouping into two primary lineages, as lineage II was not monophyletic. Based on a CYb substitution rate of 1% per million years (Myr), the major lineages are estimated to have diverged around 10 million years ago.

Chemotherapy with benznidazole and itraconazole for mice infected with different Trypanosoma cruzi clonal genotypes

The benznidazole (BZ) and itraconazole (ITC) susceptibilities of a standard set of Trypanosoma cruzi natural stocks were evaluated during the acute phase and the chronic phase of experimental chagasic infection in BALB/c mice. Twenty laboratory-cloned stocks representative of the total phylogenetic diversity of T. cruzi, including genotypes 20 and 19 (T. cruzi I) and genotypes 39 and 32 (T. cruzi II), were analyzed. Our results demonstrate important differences among stocks that could be pointed out as markers of biological behavior. Members of the T. cruzi I group were highly resistant to both BZ and ITC, whereas members of the T. cruzi II group were partially resistant to both drugs, despite their susceptibilities to ITC during the chronic phase of infection. The resistance to BZ observed for T. cruzi I was mainly triggered by genotype 20 isolates, whereas resistance to ITC was due to both genotype 20 and 19 isolates. Two polar patterns of response to BZ observed for genotype 39 isolates had a major impact on the partial resistance pattern observed for members of the T. cruzi II group. Genotype 32 isolates showed a typical profile of susceptibility. The correlation between the response to treatment and phylogenetic classification of T. cruzi stocks was clearer for ITC than for BZ. In conclusion, the data presented show a correlation between phylogenetic divergence among T. cruzi stocks and their susceptibilities to chemotherapeutic agents in vivo. Our results warn of the necessity to take into account the lesser genetic subdivisions of T. cruzi stocks since the upper subdivisions (T. cruzi I and II) show a great deal of heterogeneity for in vivo drug susceptibility.

The dog as model for chemotherapy of the Chagas' disease

In the present study, we investigated the role of dogs as experimental models for acute and chronic phases of Chagas' disease, before and after therapeutic treatments. Dogs were infected with Trypanosoma cruzi strains of different susceptibilities to benznidazole (Bz) and treated with the same therapeutic scheme as used for human chagasic. The treatment with Bz was able to prevent death and induced parasitological cure in 62.5% (acute phase) and 38.7% (chronic recent phase) of the tested animals. These results were similar to those reported in clinical trials for treated human patients (cured and uncured) in both phases of the disease. We also showed that parasitologic and serologic tests for monitoring the cure were similar to those obtained for human trials. In addition, Polymerase chain reaction showed the highest sensitivity when compared with hemoculture as an indicator of parasite clearance. In conclusion, the proposed experimental model should be relevant for chemotherapy studies for the control of Chagas' disease.

The clonal theory of parasitic protozoa: 12 years on

The question of population structure in parasitic protozoa has recently gained a renewed topicality with significant contributions on medically important pathogens, such as Plasmodium falciparum, Toxoplasma gondii and Cryptosporidium parvum. The proposals that initiated this debate are reviewed here and the subsequent developments of the clonal theory, in light of recent contributions, are examined.

Evolutionary genetics and molecular diagnosis of Leishmania species

An extensive study has been performed on various natural populations of Leishmania from the 'Old' and 'New Worlds' using multilocus enzyme electrophoresis and random amplification of polymorphic deoxyribonucleic acid. The data are interpreted in evolutionary genetic terms in order to give a firm basis to studies dealing with the relevant medical properties of pathogens. We confirm that Leishmania undergoes clonal evolution with occasional phenomena of hybridization. This suggests that the microorganism genotypes are stable in space and time and consequently have epidemiological and medical relevance. It is crucial to have a clear definition of the taxa to be identified. In the case of Leishmania, there is at present no firm consensus on the species concept. We propose that any new species of Leishmania should correspond to a 'discrete typing unit' that exhibits specific medical and/or epidemiological characters. Based on this approach, the species status of L. peruviana can be supported. On the contrary, L. panamensis cannot be clearly distinguished from L. guyanensis. Our studies on the genetic diversity of Leishmania show that a given stock is not representative of the genus, the subgenera, or any species. We suggest that the genetic polymorphism of Leishmania has a strong impact on the parasite's biomedical properties.

DNA thermodynamic pressure: a potential contributor to genome evolution

Codon usage bias is a feature of living organisms. The origin of this bias might be explained not only by external factors but also by the nature of the structure of deoxyribonucleic acid (DNA) itself. We have developed a point mutation simulation program of coding sequences, in which nucleotide replacement follows thermodynamic criteria. For this purpose we calculated the hydrogen bond-like and electrostatic energies of non-canonical base pairs in a 5 bp neighbourhood. Although the rate of non-canonical base pair formation is extremely low, such pairs occur with a preference towards a guanine (G) or cytosine (C) rather than an adenine (A) or thymine (T) replacement due to thermodynamic considerations. This feature, according to the simulation program, should result in an increase in the GC content of the genome over evolutionary time. In addition, codon bias towards a higher GC usage is also predicted. DNA sequence analysis of genes of the Trypanosomatidae lineage supported the hypothesis that DNA thermodynamic pressure is a driving force that impels increases in GC content and GC codon bias.

Impact of Trypanosoma cruzi clonal evolution on its biological properties in mice

Twenty Trypanosoma cruzi stocks attributed to the 19, 20, 39, and 32 clonal genotypes were comparatively studied in BALB/c mice during the acute and chronic phases of the infection to test the working hypothesis that T. cruzi clonal structure has a major impact on its biological properties. Fourteen parameters were assayed: (1) infectivity; (2) prepatent period; (3) patent period; (4) maximum of parasitemia; (5) day of maximum of parasitemia; (6) parasitemia; (7) mortality, (8) percentage of positive hemoculture, (9) tissue parasitism; (10) inflammatory process during the acute phase of the infection; (11) mortality, (12) percentage of positive hemoculture; (13) tissue parasitism; and (14) inflammatory process during the chronic phase of the infection. Statistical comparison showed that the results are overall consistent with the working hypothesis that biological differences are proportional to the evolutionary divergence among the genotypes. Thus, closely related genotypes (19 vs 20 and 32 vs 39) show in general fewer differences than distantly related groups (19 or 20 vs 32 or 39) except for the comparison between 19 and 32. The working hypothesis is even more strongly supported by the result of the nonparametric Mantel test, which showed a highly significant correlation (P = 2.3 x 10(-3)) between biological differences and genetic distances among all pairs of stocks. These data taken together emphasize that it is crucial to take into account the phylogenetic diversity of T. cruzi natural clones in all applied studies dealing with diagnosis, drug and vaccine design, epidemiological surveys, and clinical diversity of Chagas' disease. Index Descriptors and Abbreviations: Trypanosoma cruzi; phylogenetic distance; biological properties; clonal theory; multilocus enzyme electrophoresis (MLEE); randomly amplified polymorphic DNA (RAPD); acute phase (AP); chronic phase (CP); days after inoculation (d.a.i.); liver infusion tryptose (LIT); gastrointestinal tract (GIT); genitourinary tract (GUT); percentage of infectivity (%INF); percentage of mortality during the acute phase (%MORT AP); percentage of mortality during the chronic phase (%MORT CP); prepatent period (PPP); patent period (PP); maximum of parasitemia (MP); day of maximum of parasitemia (DMP); parasitemia (PAR); percentage of positive hemoculture during the acute phase (% + HC AP); percentage of positive hemoculture during the chronic acute phase (% + HC CP); tissue parasitism (TP); inflammatory process (IP); tissue parasitism during the acute phase (TP AP); tissue parasitism during chronic phase (TP CP); inflammatory process during acute phase (IP AP); inflammatory process chronic phase (IP CP); Mann-Whitney test (MW); Kruskal-Wallis (KW); Kolmogorow-Smirnov test (KS).

Predominance of Trypanosoma cruzi lineage I in Mexico

Randomly amplified polymorphic DNA (RAPD) has emerged as an effective genetic marker for analysis of Trypanosoma cruzi population variability. This method has been used to study the genetic variability of Mexican T. cruzi stocks and to relate these results to previous classifications. High clonal diversity was observed among the Mexican populations: 24 RAPD types were scored among 56 stocks analyzed. Only two stocks (3.6%) belonged to the T. cruzi II lineage, while all others belonged to T. cruzi I. The robustness of these clusters was statistically highly significant. Mexican T. cruzi I stocks formed a homogeneous group with reduced genetic distances among its members. Parasites from this group were isolated from both domestic and sylvatic cycles over a broad geographic area in Mexico. The two Mexican stocks classified as T. cruzi II (isolated from sylvatic cycles) were of the same RAPD type, although they were not closely related to the three reference T. cruzi II stocks circulating in domestic cycles in Argentina, Brazil, Bolivia, and Chile. These stocks were also unrelated to the formerly named Zymodeme III.

Variation in susceptibility to benznidazole in isolates derived from Trypanosoma cruzi parental strains

In this work, the susceptibility to benznidazole of two parental Trypanosoma cruzi strains, Colombian and Berenice-78, was compared to isolates obtained from dogs infected with these strains for several years. In order to evaluate the susceptibility to benznidazole two groups of mice were infected with one of five distinct populations isolated from dogs as well as the two parental strains of T. cruzi. The first group was treated with benznidazole during the acute phase and the second remained untreated controls. The animals were considered cured when parasitological and serological tests remained persistently negative. Mice infected with the Colombian strain and its isolates Colombian (A and B) did not cure after treatment. On the other hand, all animals infected with Berenice-78 were cured by benznidazole treatment. However, 100%, 50% and 70% of cure rates were observed in animals infected with the isolates Berenice-78 B, C and D, respectively. No significant differences were observed in serological profile of infected control groups, with all animals presenting high antibody levels. However, the ELISA test showed differences in serological patterns between mice inoculated with the different T. cruzi isolates and treated with benznidazole. This variability was dependent on the T. cruzi population used and seemed to be associated with the level of resistance to benznidazole.