Trypanosoma cruzi: presence of the two major phylogenetic lineages and of several lesser discrete typing units (DTUs) in Chile and Paraguay

A panel of phenotypically and genotypically diverse bioluminescent:fluorescent Trypanosoma cruzi strains as a resource for Chagas disease research

Chagas disease is caused by Trypanosoma cruzi, a protozoan parasite that displays considerable genetic diversity. Infections result in a range of pathological outcomes, and different strains can exhibit a wide spectrum of anti-parasitic drug tolerance. The genetic determinants of infectivity, virulence and therapeutic susceptibility remain largely unknown. As experimental tools to address these issues, we have generated a panel of bioluminescent:fluorescent parasite strains that cover the diversity of the T. cruzi species. These reporters allow spatio-temporal infection dynamics in murine models to be monitored in a non-invasive manner by in vivo imaging, provide a capability to detect rare infection foci at single-cell resolution, and represent a valuable resource for investigating virulence and host:parasite interactions at a mechanistic level. Importantly, these parasite reporter strains can also contribute to the Chagas disease drug screening cascade by ensuring that candidate compounds have pan-species in vivo activity prior to being advanced into clinical testing. The parasite strains described in this paper are available on request.

Survivorship of wild caught Mepraia spinolai nymphs: The effect of seasonality and Trypanosoma cruzi infection after feeding and fasting in the laboratory

Chagas disease is caused by Trypanosoma cruzi. Vector survival is an important variable affecting vectorial capacity to determine parasite transmission risk. The aims of this study are to evaluate vector survival under fasting/starvation conditions of wild-caught Mepraia spinolai after feeding and fasting, the pathogenicity of T. cruzi infection, the parasite burden and seasonal variation in parasite discrete typing units (DTU). The survivorship of M. spinolai nymphs after two continuous artificial feedings was evaluated, assessing their infection with microscopic observation of fecal samples and PCR. Later, insects were fasted/starved until death. We performed qPCR analyses of parasite load in the fecal samples and dead specimens. T. cruzi genotyping was performed using conventional PCR amplicons and hybridization tests. Infection rate was higher in M. spinolai nymphs in summer and spring than in fall. Parasite burden varied from 3 to 250,000 parasites/drop. Survival rate for starved nymph stage II was lower in insects collected in the spring compared to summer and fall. TcII was the most frequent DTU. Mainly metacyclic trypomastigotes were excreted. We conclude that M. spinolai infection rate in nymphs varies among seasons, suggesting higher transmission risk in warmer seasons. However, nymphs stage II collected in spring are more sensitive to starvation compared to other seasons. TcII in single or mixed infection does not seem relevant to determine vector pathogenicity. These results of vector survivorship after fasting/starvation are important to determine the competence of M. spinolai as a vector of T. cruzi, since they excrete metacyclic trypomastigotes and the parasitism with T. cruzi seems to be poorly pathogenic to the vector under a severe fasting/starvation condition.

Within-host temporal fluctuations of Trypanosoma cruzi discrete typing units: the case of the wild reservoir rodent Octodon degus

Background

Chagas disease caused by Trypanosoma cruzi is considered a major public health problem in America. After an acute phase the disease changes to a chronic phase with very low parasitemia. The parasite presents high genetic variability with seven discrete typing units (DTUs): TcI-TcVI and Tc bat. The aim of this work is to evaluate fluctuation of parasitemia and T. cruzi DTUs in naturally infected Octodon degus.

Methods

After animal capture parasitemia was obtained by qPCR and later the animals were evaluated by three serial xenodiagnoses using two insect vector species, Mepraia spinolai and Triatoma infestans. The parasites amplified over time by insect xenodiagnosis were analyzed by conventional PCR and after that the infective T. cruzi were characterized by means of hybridization tests.

Results

The determination of O. degus parasitemia before serial xenodiagnosis by qPCR reveals a great heterogeneity from 1 to 812 parasite equivalents/ml in the blood stream. The T. cruzi DTU composition in 23 analyzed animals by xenodiagnosis oscillated from mixed infections with different DTUs to infections without DTU identification or vice versa, this is equivalent to 50% of the studied animals. Detection of triatomine infection and composition of T. cruzi DTUs was achieved more efficiently 40 days post-infection rather than after 80 or 120 days.

Conclusion

Trypanosoma cruzi DTUs composition fluctuates over time in naturally infected O. degus. Three replicates of serial xenodiagnosis confirmed that living parasites have been studied. Our results allow us to confirm that M. spinolai and T. infestans are equally competent to maintain T. cruzi DTUs since similar results of infection were obtained after xenodiagnosis procedure.

Direct identification of trypanosomatids by matrix-assisted laser desorption ionization-time of flight mass spectrometry (DIT MALDI-TOF MS)

Accurate and rapid determination of trypanosomatids is essential in epidemiological surveillance and therapeutic studies. Matrix-assisted laser desorption ionization/time of flight mass spectrometry (MALDI-TOF MS) has been shown to be a useful and powerful technique to identify bacteria, fungi, metazoa and human intact cells with applications in clinical settings. Here, we developed and optimized a MALDI-TOF MS method to profile trypanosomatids. trypanosomatid cells were deposited on a MALDI target plate followed by addition of matrix solution. The plate was then subjected to MALDI-TOF MS measurement to create reference mass spectra library and unknown samples were identified by pattern matching using the BioTyper software tool. Several m/z peaks reproducibly and uniquely identified trypanosomatids species showing the potentials of direct identification of trypanosomatids by MALDI-TOF MS. Moreover, this method discriminated different life stages of Trypanosoma cruzi, epimastigote and bloodstream trypomastigote and Trypanosoma brucei, procyclic and bloodstream. T. cruzi Discrete Typing Units (DTUs) were also discriminated in three clades. However, it was not possible to achieve enough resolution and software-assisted identification at the strain level. Overall, this study shows the importance of MALDI-TOF MS for the direct identification of trypanosomatids and opens new avenues for mass spectrometry-based detection of parasites in biofluids. Copyright © 2016 John Wiley & Sons, Ltd.

TcI Isolates of Trypanosoma cruzi Exploit the Antioxidant Network for Enhanced Intracellular Survival in Macrophages and Virulence in Mice

Trypanosoma cruzi species is categorized into six discrete typing units (TcI to TcVI) of which TcI is most abundantly noted in the sylvatic transmission cycle and considered the major cause of human disease. In our study, the TcI strains Colombiana (COL), SylvioX10/4 (SYL), and a cultured clone (TCC) exhibited different biological behavior in a murine model, ranging from high parasitemia and symptomatic cardiomyopathy (SYL), mild parasitemia and high tissue tropism (COL), to no pathogenicity (TCC). Proteomic profiling of the insect (epimastigote) and infective (trypomastigote) forms by two-dimensional gel electrophoresis/matrix-assisted laser desorption ionization-time of flight mass spectrometry, followed by functional annotation of the differential proteome data sets (≥2-fold change, P < 0.05), showed that several proteins involved in (i) cytoskeletal assembly and remodeling, essential for flagellar wave frequency and amplitude and forward motility of the parasite, and (ii) the parasite-specific antioxidant network were enhanced in COL and SYL (versus TCC) trypomastigotes. Western blotting confirmed the enhanced protein levels of cytosolic and mitochondrial tryparedoxin peroxidases and their substrate (tryparedoxin) and iron superoxide dismutase in COL and SYL (versus TCC) trypomastigotes. Further, COL and SYL (but not TCC) were resistant to exogenous treatment with stable oxidants (H2O2 and peroxynitrite [ONOO(-)]) and dampened the intracellular superoxide and nitric oxide response in macrophages, and thus these isolates escaped from macrophages. Our findings suggest that protein expression conducive to increase in motility and control of macrophage-derived free radicals provides survival and persistence benefits to TcI isolates of T. cruzi.

Interactions Between Trypanosoma cruzi the Chagas Disease Parasite and Naturally Infected Wild Mepraia Vectors of Chile

Chagas disease, which ranks among the world's most neglected diseases, is a chronic, systemic, parasitic infection caused by the protozoan Trypanosoma cruzi. Mepraia species are the wild vectors of this parasite in Chile. Host-parasite interactions can occur at several levels, such as co-speciation and ecological host fitting, among others. Thus, we are exploring the interactions between T. cruzi circulating in naturally infected Mepraia species in all areas endemic of Chile. We evaluated T. cruzi infection rates of 27 different haplotypes of the wild Mepraia species and identified their parasite genotypes using minicircle PCR amplification and hybridization tests with genotype-specific DNA probes. Infection rates were lower in northern Chile where Mepraia gajardoi circulates (10-35%); in central Chile, Mepraia spinolai is most abundant, and infection rates varied in space and time (0-55%). T. cruzi discrete typing units (DTUs) TcI, TcII, TcV, and Tc VI were detected. Mixed infections with two or more DTUs are frequently found in highly infected insects. T. cruzi DTUs have distinct, but not exclusive, ecological and epidemiological associations with their hosts. T. cruzi infection rates of M. spinolai were higher than in M. gajardoi, but the presence of mixed infection with more than one T. cruzi DTU was the same. The same T. cruzi DTUs (TcI, TcII, TcV, and TcVI) were found circulating in both vector species, even though TcI was not equally distributed. These results suggest that T. cruzi DTUs are not associated with any of the two genetically related vector species nor with the geographic area. The T. cruzi vectors interactions are discussed in terms of old and recent events. By exploring T. cruzi DTUs present in Mepraia haplotypes and species from northern to central Chile, we open the analysis on these invertebrate host-parasite interactions.

Geographic variation of Trypanosoma cruzi discrete typing units from Triatoma infestans at different spatial scales

We assessed the diversity and distribution of Trypanosoma cruzi discrete typing units (DTU) in Triatoma infestans populations and its association with local vector-borne transmission levels at various geographic scales. At a local scale, we found high predominance (92.4%) of TcVI over TcV in 68 microscope-positive T. infestans collected in rural communities in Santiago del Estero province in northern Argentina. TcV was more often found in communities with higher house infestation prevalence compatible with active vector-borne transmission. Humans and dogs were the main bloodmeal sources of the TcV- and TcVI-infected bugs. At a broader scale, the greatest variation in DTU diversity was found within the Argentine Chaco (227 microscope-positive bugs), mainly related to differences in equitability between TcVI and TcV among study areas. At a country-wide level, a meta-analysis of published data revealed clear geographic variations in the distribution of DTUs across countries. A correspondence analysis showed that DTU distributions in domestic T. infestans were more similar within Argentina (dominated by TcVI) and within Bolivia (where TcI and TcV had similar relative frequencies), whereas large heterogeneity was found within Chile. DTU diversity was lower in the western Argentine Chaco region and Paraguay (D=0.14-0.22) than in the eastern Argentine Chaco, Bolivia and Chile (D=0.20-0.68). Simultaneous DTU identifications of T. cruzi-infected hosts and triatomines across areas differing in epidemiological status are needed to shed new light on the structure and dynamics of parasite transmission cycles.

Molecular and biological characterization of Trypanosoma cruzi strains isolated from children from Jequitinhonha Valley, State of Minas Gerais, Brazil

INTRODUCTION

The biological diversity of Trypanosoma cruzi strains plays an important role in the clinical and epidemiological features of Chagas disease.

METHODS

Eight T. cruzi strains isolated from children living in a Chagas disease vector-controlled area of Jequitinhonha Valley, State of Minas Gerais, Brazil, were genetically and biologically characterized.

RESULTS

The characterizations demonstrated that all of the strains belonged to T. cruzi II, and showed high infectivity and a variable mean maximum peak of parasitemia. Six strains displayed low parasitemia, and two displayed moderate parasitemia. Later peaks of parasitemia and a predominance of intermediate and large trypomastigotes in all T. cruzi strains were observed. The mean pre-patent period was relatively short (4.2 ± 0.25 to 13.7 ± 3.08 days), whereas the patent period ranged from 3.3 ± 1.08 to 34.5 ± 3.52 days. Mortality was observed only in animals infected with strain 806 (62.5%). Histopathological analysis of the heart showed that strains 501 and 806 caused inflammation, but fibrosis was observed only in animals infected with strain 806.

CONCLUSIONS

The results indicate the presence of an association between the biological behavior in mice and the genetic characteristics of the parasites. The study also confirmed general data from Brazil where T. cruzi II lineage is the most prevalent in the domiciliary cycle and generally has low virulence, with some strains capable of inducing inflammatory processes and fibrosis.

Discrete typing units of Trypanosoma cruzi identified in rural dogs and cats in the humid Argentinean Chaco

The discrete typing units (DTUs) of Trypanosoma cruzi that infect domestic dogs and cats have rarely been studied. With this purpose we conducted a cross-sectional xenodiagnostic survey of dog and cat populations residing in 2 infested rural villages in Pampa del Indio, in the humid Argentine Chaco. Parasites were isolated by culture from 44 dogs and 12 cats with a positive xenodiagnosis. DTUs were identified from parasite culture samples using a strategy based on multiple polymerase-chain reactions. TcVI was identified in 37 of 44 dogs and in 10 of 12 cats, whereas TcV was identified in 5 dogs and in 2 cats -a new finding for cats. No mixed infections were detected. The occurrence of 2 dogs infected with TcIII -classically found in armadillos- suggests a probable link with the local sylvatic transmission cycle involving Dasypus novemcinctus armadillos and a potential risk of human infection with TcIII. Our study reinforces the importance of dogs and cats as domestic reservoir hosts and sources of various DTUs infecting humans, and suggests a link between dogs and the sylvatic transmission cycle of TcIII.

Presence of Trypanosoma cruzi in pregnant women and typing of lineages in congenital cases

The objective of this study was to determine the presence of Trypanosoma cruzi in blood samples of mothers with chronic Chagas disease and their newborn by conventional PCR targeted to minicircle kinetoplastidic DNA (kDNA), and to determine the lineages in mother/newborn pairs of the congenital cases by hybridization assays with probes belonging to the TcII, TcI and TcV Discrete Typing Units (DTU). In 63 (57.2%) of the mothers the presence of circulating T. cruzi was demonstrated by PCR immediately before delivery and in three newborn (3%) congenital transmission was confirmed by serial PCR and conventional serology between 1 and 16 months of life, at which point treatment was started. The hybridization signals showed that two of the newborn had the same DTU as their mother (TcI, TcII and TcV), whilst in the third congenital case only TcV was detected in the cord blood, suggesting that in this infant TcI and TcII did not cross the placenta or the parasite was not present at a detectable level. Levels T. cruzi DNA was determined by TaqMan Probe based Real Time PCR assay targeted to nuclear satellite sequences in these three pairs of samples.

Differential pattern of infection of sylvatic nymphs and domiciliary adults of Triatoma infestans with Trypanosoma cruzi genotypes in Chile

In Chile, the main vector of Chagas disease, Triatoma infestans, is under control after insecticide spraying. However, it has been found colonizing wild habitats. This study evaluated Trypanosoma cruzi infection of sylvatic and domiciliary T. infestans and identified their parasite genotypes. The sample studied was composed mainly of T. infestans sylvatic nymphs and domiciliary adults from a semi-urban area with human dwellings under vector control surveillance. Results showed prevalences of 57.7% in nymphs and 68.6% in adults. Hybridization tests showed a major T. cruzi lineage (TcI) circulating in sylvatic (93.3%) and domiciliary (100%) T. infestans. TcII, TcV, and TcVI were also detected, mainly in nymphs, suggesting differential adaptation of T. cruzi lineages among instars. We also discuss the origin of domiciliary individuals of T. infestans and the risk of human infection by triatomines of sylvatic foci that invade houses despite vector control programs.

Trypanosoma cruzi genotypes of insect vectors and patients with Chagas of Chile studied by means of cytochrome b gene sequencing, minicircle hybridization, and nuclear gene polymorphisms

Fifty-six Trypanosoma cruzi stocks from Chile and neighboring countries and different hosts, humans, and Triatoma infestans and Mepraia sp., vectors of domiciliary and natural environments were characterized by using three molecular markers. These were cytochrome b (Cyt b) gene sequencing, minicircle DNA blotting, and hybridization with five genotype-specific DNA probes and nuclear analysis of 1f8 and gp72 by polymerase chain reaction-restriction fragment length polymorphism. The results with all three molecular markers are concordant, with minor limitations, grouping T. cruzi stocks into four discrete typing units (DTUs) (TcI, TcII, TcV, and TcVI). TcI and TcII stocks were heterogeneous. TcI and TcII stocks were clustered in two main subgroups determined by Cyt b gene sequencing and minicircle hybridization. However, TcV and TcVI stocks were homogeneous and not differentiated by Cyt b gene sequencing or minicircle DNA hybridization. The discriminatory power and limitations of the molecular markers are discussed, as well as the distribution of the four DTUs in the domiciliary and sylvatic transmission cycles of Chile and the limitations of each marker for molecular epidemiological studies performed with T. cruzi stocks rather than the analysis of direct T. cruzi samples from natural hosts.

Recent, independent and anthropogenic origins of Trypanosoma cruzi hybrids

The single celled eukaryote Trypanosoma cruzi, a parasite transmitted by numerous species of triatomine bug in the Americas, causes Chagas disease in humans. T. cruzi generally reproduces asexually and appears to have a clonal population structure. However, two of the six major circulating genetic lineages, TcV and TcVI, are TcII-TcIII inter-lineage hybrids that are frequently isolated from humans in regions where chronic Chagas disease is particularly severe. Nevertheless, a prevalent view is that hybridisation events in T. cruzi were evolutionarily ancient and that active recombination is of little epidemiological importance. We analysed genotypes of hybrid and non-hybrid T. cruzi strains for markers representing three distinct evolutionary rates: nuclear GPI sequences (n = 88), mitochondrial COII-ND1 sequences (n = 107) and 28 polymorphic microsatellite loci (n = 35). Using Maximum Likelihood and Bayesian phylogenetic approaches we dated key evolutionary events in the T. cruzi clade including the emergence of hybrid lineages TcV and TcVI, which we estimated to have occurred within the last 60,000 years. We also found evidence for recent genetic exchange between TcIII and TcIV and between TcI and TcIV. These findings show that evolution of novel recombinants remains a potential epidemiological risk. The clearly distinguishable microsatellite genotypes of TcV and TcVI were highly heterozygous and displayed minimal intra-lineage diversity indicative of even earlier origins than sequence-based estimates. Natural hybrid genotypes resembled typical meiotic F1 progeny, however, evidence for mitochondrial introgression, absence of haploid forms and previous experimental crosses indicate that sexual reproduction in T. cruzi may involve alternatives to canonical meiosis. Overall, the data support two independent hybridisation events between TcII and TcIII and a recent, rapid spread of the hybrid progeny in domestic transmission cycles concomitant with, or as a result of, disruption of natural transmission cycles by human activities.

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.

Flow cytometric analysis and microsatellite genotyping reveal extensive DNA content variation in Trypanosoma cruzi populations and expose contrasts between natural and experimental hybrids

Trypanosoma cruzi exhibits remarkable genetic heterogeneity. This is evident at the nucleotide level but also structurally, in the form of karyotypic variation and DNA content differences between strains. Although natural populations of T. cruzi are predominantly clonal, hybrid lineages (TcIId and TcIIe) have been identified and hybridisation has been demonstrated in vitro, raising the possibility that genetic exchange may continue to shape the evolution of this pathogen. The mechanism of genetic exchange identified in the laboratory is unusual, apparently involving fusion of diploid parents followed by genome erosion. We investigated DNA content diversity in natural populations of T. cruzi in the context of its genetic subdivisions by using flow cytometric analysis and multilocus microsatellite genotyping to determine the relative DNA content and estimate the ploidy of 54 cloned isolates. The maximum difference observed was 47.5% between strain Tu18 cl2 (TcIIb) and strain C8 cl1 (TcI), which we estimated to be equivalent to ∼73 Mb of DNA. Large DNA content differences were identified within and between discrete typing units (DTUs). In particular, the mean DNA content of TcI strains was significantly less than that for TcII strains (P < 0.001). Comparisons of hybrid DTUs TcIId/IIe with corresponding parental DTUs TcIIb/IIc indicated that natural hybrids are predominantly diploid. We also measured the relative DNA content of six in vitro-generated TcI hybrid clones and their parents. In contrast to TcIId/IIe hybrid strains these experimental hybrids comprised populations of sub-tetraploid organisms with mean DNA contents 1.65–1.72 times higher than the parental organisms. The DNA contents of both parents and hybrids were shown to be relatively stable after passage through a mammalian host, heat shock or nutritional stress. The results are discussed in the context of hybridisation mechanisms in both natural and in vitro settings.

The molecular epidemiology and phylogeography of Trypanosoma cruzi and parallel research on Leishmania: looking back and to the future

Trypanosoma cruzi is the protozoan agent of Chagas disease, and the most important parasitic disease in Latin America. Protozoa of the genus Leishmania are global agents of visceral and cutaneous leishmaniasis, fatal and disfiguring diseases. In the 1970s multilocus enzyme electrophoresis demonstrated that T. cruzi is a heterogeneous complex. Six zymodemes were described, corresponding with currently recognized lineages, TcI and TcIIa-e – now defined by multiple genetic markers. Molecular epidemiology has substantially resolved the phylogeography and ecological niches of the T. cruzi lineages. Genetic hybridization has fundamentally influenced T. cruzi evolution and epidemiology of Chagas disease. Genetic exchange of T. cruzi in vitro involves fusion of diploids and genome erosion, producing aneuploid hybrids. Transgenic fluorescent clones are new tools to elucidate molecular genetics and phenotypic variation. We speculate that pericardial sequestration plays a role in pathogenesis. Multilocus sequence typing, microsatellites and, ultimately, comparative genomics are improving understanding of T. cruzi population genetics. Similarly, in Leishmania, genetic groups have been defined, including epidemiologically important hybrids; genetic exchange can occur in the sand fly vector. We describe the profound impact of this parallel research on genetic diversity of T. cruzi and Leishmania, in the context of epidemiology, taxonomy and disease control.

Haplotype identification within Trypanosoma cruzi I in Colombian isolates from several reservoirs, vectors and humans

Genetic variability in the Trypanosoma cruzi I group has recently been revealed in Colombian isolates from humans, reservoirs and vectors. Genomic rearrangements and the polymorphic regions in taxonomic markers, such as the miniexon gene, have led to the development of molecular tools to identify phylogenetic haplotypes in T. cruzi isolates. From genetic polymorphisms found in T. cruzi I isolates, they have been classified into four haplotypes according to their epidemiologic transmission cycles. Haplotype Ia is associated with domestic isolates, from Rhodnius prolixus; haplotype Ib, with the domestic and peridomestic cycle, mainly associated with Triatoma dimidiata; haplotype Ic is a poorly characterized group, which has been associated with the peridomestic cycle; and haplotype Id has been related to the sylvatic cycle. In order to demonstrate that the circulating T. cruzi I isolates in Colombia can be classified in the four proposed haplotypes, specific primers were designed on polymorphic regions of the miniexon gene's intergenic sequences. This set of primers allowed the molecular characterization of 33 Colombian isolates, classifying them into three of the four proposed haplotypes (Ia, Ib and Id). Results obtained from maximum parsimony and maximum-likelihood-based phylogenetic analyses correlated with the molecular classification of the isolates and their transmission cycles. This study brings insights into the Chagas disease epidemiology and the parasite's transmission dynamics.

Congenital Chagas disease involves Trypanosoma cruzi sub-lineage IId in the northwestern province of Salta, Argentina

Trypanosoma cruzi is genetically classified into six discrete phylogenetic lineages on the basis of different genetic markers. Identifying lineages circulating among humans in different areas is essential to understand the molecular epidemiology of Chagas disease. In the present study, 18 T. cruzi isolates from congenitally infected newborns in the northwestern province of Salta-Argentina were studied by multilocus enzyme electrophoresis (MLEE) and random amplified polymorphic DNA (RAPD). All isolates were typed by MLEE and RAPD as belonging to T. cruzi IId. Analysis of minor variants of TcIId using probes hybridizing with hypervariable domains of kDNA minicircles, detected three variants with a similar distribution among the isolates. Our findings confirm the presence of T. cruzi IId among congenitally infected newborns in northwestern Argentina and support the assumption that human infection by T. cruzi in the Southern Cone countries of Latin America is due principally to T. cruzi II.

Genetic heterogeneity in Trypanosoma cruzi strains from naturally infected triatomine vectors in northeastern Brazil: epidemiological implications

Eighteen Trypanosoma cruzi strains isolated from naturally infected triatomines were studied genetically. The majority of the strains were from Triatoma brasiliensis, the principal vector of Chagas disease in the northeast of Brazil. Multilocus enzyme electrophoresis (MLEE) and randomly amplified polymorphic DNA (RAPD) analyses were used to investigate the genotypic diversity and the spread of the T. cruzi genotypes in different environments. MLEE clearly distinguished two distinct isoenzyme profiles, and RAPD analysis revealed 10 different genotypes circulating in rural areas. The strains could be typed as isoenzyme variants of the T. cruzi principal zymodeme Z1 (T. cruzi I). An effective program of epidemiological vigilance is required to prevent the spread of T. cruzi I strains into human dwellings.

Direct molecular profiling of minicircle signatures and lineages of Trypanosoma cruzi bloodstream populations causing congenital Chagas disease

Congenital transmission of Trypanosoma cruzi may occur in some or all the gestations from a T. cruzi-infected mother. Variable rates of congenital transmission have been reported in different geographical areas where different parasitic strains predominate, suggesting that parasitic genotypes might play a role in the risk of congenital transmission. Moreover, in cases of transmission it is unknown if the whole maternal T. cruzi population or certain clones are preferentially transmitted by the transplacental route. In this study, bloodstream T. cruzi lineages were identified in blood samples from congenitally infected children, transmitting and non-transmitting mothers and unrelated Chagas disease patients, using improved PCR strategies targeted to nuclear genomic markers. T. cruzi IId was the prevalent genotype among 36/38 PCR-positive congenitally infected infants, 5/5 mothers who transmitted congenital Chagas disease, 12/13 mothers who delivered non-infected children and 28/34 unrelated Chagas disease patients, all coming from endemic localities of Argentina and Bolivia. These figures indicate no association between a particular genotype and vertical transmission. Furthermore, minicircle signatures from the maternal and infants' bloodstream trypanosomes were profiled by restriction fragment length polymorphism of the 330-bp PCR-amplified variable regions in seven cases of mothers and congenitally infected infants. Minicircle signatures were nearly identical between each mother and her infant/s and unique to each mother-infant/s case, a feature that was also observed in twin deliveries. Moreover, allelic size polymorphism analysis of microsatellite loci from populations transmitted to twins showed that all clones from the maternal polyclonal population were equally infective to both siblings.

Current status and future prospects for a vaccine against American trypanosomiasis

The clinically relevant pathognomonic consequences of human infection by Trypanosoma cruzi are dilation and hypertrophy of the left ventricle walls and thinning of the apex. The major complications and debilitating evolutionary outcomes of chronic infection include ventricular fibrillation, thromboembolism and congestive heart failure. American trypanosomiasis (Chagas disease) poses serious public healthcare and budgetary concerns. The currently available drugs, although effective against acute infection, are highly toxic and ineffective in arresting or attenuating clinical disease symptoms in chronic patients. The development of an efficacious prophylactic vaccine faces many challenges, and progress is slow, despite several years of effort. Studies in animal models and human patients have revealed the pathogenic mechanisms during disease progression, pathology of disease and features of protective immunity. Accordingly, several antigens, antigen-delivery vehicles and adjuvants have been tested in animal models, and some efforts have been successful in controlling infection and disease. This review will summarize the accumulated knowledge about the parasite and disease, as well as pathogenesis and protective immunity. The authors will discuss the efforts to date, and the challenges faced in achieving an efficient prophylactic vaccine against human American trypanosomiasis, and present the future perspectives.

Mechanisms of pathogenesis in Chagas disease

Chagas disease, caused by the obligate unicellular parasite Trypanosoma cruzi, presents itself in a diverse collection of clinical manifestations, ranging from severe, fatal heart and digestive tract pathologies to unapparent or minor alterations that do not compromise survival. Over the years, a number of mechanisms have been proposed to explain the pathogenesis of chagasic tissue lesions, all of which have faced some criticism or been received with skepticism. This article excludes the autoimmunity hypothesis for Chagas disease because it has been extensively reviewed elsewhere, and summarizes the various alternative hypotheses that have been advanced over the years. For each of these hypotheses, an outline of its main tenets and key findings that support them is presented. This is followed by the results and comments that have challenged them and the caveats that stand on their way to wider acceptance. It is hoped that this writing will draw attention to our shortcomings in understanding the pathogenesis of Chagas disease, which, unfortunately, continues to figure among the most serious health problems of the American continent.

Two Hybridization Events Define the Population Structure of Trypanosoma cruzi

Genetic variation in Trypanosoma cruzi is likely a key determinant in transmission and pathogenesis of Chagas disease. We have examined nine loci as markers for the extant T. cruzi strains. Four distinct alleles were found for each locus, corresponding to the sequence classes present in the homozygous discrete typing units (DTUs) I, IIa, IIb, and IIc. The alleles in DTUs IIa and IIc showed a spectrum of polymorphism ranging from DTU I-like to DTU IIb-like, in addition to DTU-specific sequence variation. DTUs IId and IIe were indistinguishable, showing DTU homozygosity at one locus and heterozygosity with DTU IIb and IIc allelic sequences at eight loci. Recombination between the DTU IIb and IIc alleles is evidenced from mosaic polymorphisms. These data imply that two discrete hybridization events resulted in the formation of the current DTUs. We propose a model in which a fusion between ancestral DTU I and IIb strains gave rise to a heterozygous hybrid that homogenized its genome to become the homozygous progenitor of DTUs IIa and IIc. The second hybridization between DTU IIb and IIc strains that generated DTUs IId and IIe resulted in extensive heterozygosity with subsequent recombination of parental genotypes.

Predominance of lineage I among Trypanosoma cruzi isolates from Venezuelan patients with different clinical profiles of acute Chagas' disease

Trypanosoma cruzi isolates from 23 acute chagasic patients from localities of Western Venezuela (state of Barinas) where Chagas' disease is endemic were typed using ribosomal and mini-exon gene markers. Results showed that isolates of the two major phylogenetic lineages, T. cruzi I and T. cruzi II, were isolated from these patients. Six isolates (26%) were typed as T. cruzi II and 17 (74%) as belonging to T. cruzi lineage I. Analysis of random amplified polymorphic DNA (RAPD) patterns confirmed these two groups of isolates, but did not disclose significant genetic intra-lineage polymorphism. Patients infected by both T. cruzi I or T. cruzi II showed different clinical profiles presenting highly variable signs and symptoms of acute phase of Chagas' disease ranging from totally asymptomatic to severe heart failure. The predominance of T. cruzi I human isolates in Venezuela allied to the higher prevalence of severe symptoms of Chagas' disease (heart failure) in patients infected by this lineage do not corroborate an innocuousness of T. cruzi I infection to humans. To our knowledge, this is the first study describing predominance of T. cruzi lineage I in a large number of acute chagasic patients with distinct and well-characterized clinical profiles.

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.