Trypanosoma cruzi: genetic group with peculiar biochemical and biological behavior

Infection susceptibility and vector competence of Rhodnius robustus Larrousse, 1927 and R. pictipes Stal, 1872 (Hemiptera, Reduviidae, Triatominae) for strains of Trypanosoma cruzi (Chagas, 1909) (Kinetoplastida, Trypanosomatidae) I, II and IV

Background

Rhodnius robustus and Rhodnius pictipes are vectors of Trypanosoma cruzi, the etiologic agent of Chagas disease (CD), that are found in the Brazilian Amazon region. Susceptibility to infection and vector competence depend on the parasite-vector relationship. Our objective was to evaluate the interaction between T. cruzi and these two triatomine vectors in pure and mixed experimental infections of T. cruzi strains from the same or different geographic regions.

Methods

Fifth-instar nymphs of R. robustus and R. pictipes were fed on mice infected with four T. cruzi strains, namely genotypes TcIAM, TcIMG, TcIIPR, and TcIVAM, respectively, from the Brazilian states of Amazonas, Minas Gerais and Paraná. Over a period of 120 days, excreta were examined every 20 days to assess vector competence, and intestinal contents (IC) were examined every 30 days to determine susceptibility to infection.

Results

The highest positive rate in the fresh examination (%+FE, 30.0%), the highest number of parasitic forms (PF, n = 1969) and the highest metacyclogenesis rate (%MC, 53.8%) in the excreta were recorded for R. robustus/TcIVAM. Examination of the IC of R. pictipes revealed a higher number of PF in infections with TcIAM (22,680 PF) and TcIIPR (19,845 PF) alone or in association (17,145 PF), as well as a %+FE of 75.0% with TcII, in comparison with the other genotypes. The highest %MC (100%) was recorded for the mixed infections of TcIAM with TcIIPR or TcIVAM in the IC of R. pictipes.

Conclusions

Overall, both species were found to be susceptible to the T. cruzi strains studied. Rhodnius robustus showed vector competence for genotypes TcIVAM and TcIAM+TcIVAM and R. pictipes for TcIAM+TcIVAM and TcIAM+TcIIPR; there was elimination of infective forms as early as at 20 days. Our results suggest that both the genetics of the parasite and its geographic origin influence the susceptibility to infection and vector competence, alone or in association.

Graphical Abstract

Therapeutic effects of benznidazole in Swiss mice that are orally inoculated with Trypanosoma cruzi IV strains from the Western Brazilian Amazon

Strains of Trypanosoma cruzi, etiological agent of Chagas disease, are classified into different discrete typing units that may present distinct dynamics of infection and susceptibility to benznidazole (BZ) treatment. Mice that were orally inoculated with T. cruzi IV strains exhibited a more intense course of infection compared with intraperitoneally inoculated mice, reflected by higher parasite loads. We evaluated the efficacy of BZ treatment in Swiss mice that were inoculated with T. cruzi IV strains from the Western Brazilian Amazon. The mice were orally (OR) or intraperitoneally (IP) inoculated with 2 × 10⁶ culture-derived metacyclic trypomastigotes of the AM14, AM16, AM64, and AM69 strains of T. cruzi that were obtained from two outbreaks of orally acquired acute Chagas disease in the state of Amazonas, Brazil. The animals were treated with BZ (100 mg/kg/day for 20 days). Fresh blood examination, hemoculture, conventional and quantitative real-time polymerase chain reaction were performed to monitor the therapeutic effects of BZ. Significant reductions in five of 24 parameters of parasitemia and parasite load were found in different tissues in the OR group, indicating worse response to BZ treatment compared with the IP group, in which significant reductions in nine of those 24 parameters were observed. The cure rates in the OR groups ranged from 18.2% (1/11) to 75.0% (9/12) and in the IP groups from 58.3% (7/12) to 91.7% (11/12), for the AM14 and AM69 strains, respectively. These findings indicate that treatment with BZ had fewer beneficial effects with regard to reducing parasitemia and parasite load in different tissues of mice that were OR inoculated with four TcIV strains compared with IP inoculation. Therefore, the route of infection with T. cruzi should be considered when evaluating the therapeutic efficacy of BZ in patients with Chagas disease.

Morphobiological, morphometric and ultrastructural characterization of sylvatic Trypanosoma cruzi isolates from Rio de Janeiro state, Brazil

Abstract Triatoma vitticeps is a triatomine with geographic distribution restrict to Brazil, which exhibits high prevalence of Trypanosoma cruzi natural infection. Of special epidemiologic concern, this species often invades households in the states of Rio de Janeiro, Minas Gerais and Espírito Santo. The objective of this study was to evaluate morphological and ultrastructural parameters on three T. cruzi isolates obtained from wild T. vitticeps specimens. The growth and cell differentiation of the parasite was evaluated through epimastigote and trypomastigote forms obtained in the growth curves for three distinct isolates. The maximum growth showed differences at the 20th day of the curve. Our in vitro results show a heterogeneity, regarding these features for samples cultivated under the same conditions. Morphometric analyzes based on the shape of epimastigotes and trypomastigotes corroborated such differentiation. These results highlight the need of better understanding the meaning of this diversity under an eco-epidemiological perspective.

How do biting disease vectors behaviourally respond to host availability?

BACKGROUND

Ecological theory predicts a diverse range of functional responses of species to resource availability; but in the context of human blood consumption by disease vectors, a simplistic, linear response is ubiquitously assumed. A simple and flexible model formulation is presented that extends the Holling's Types to account for a wider range of qualitatively distinct behaviours, and used to examine the impact of different vector responses to the relative availability of multiple blood-host species.

RESULTS

Epidemiological models of falciparum malaria, Chagas disease and Lyme disease demonstrate that the standard, often implicit, assumption of a linear functional response can lead to spurious under- or over-estimates in disease transmission potential, across a full range of pathogen life-cycles. It is shown how the functional response in vector biting can augment disease intervention outcomes. Interactions between vector biting behaviour and uneven pathogen transmission probabilities between alternative hosts, as is the case for Chagas disease, can render infection more resilient to control.

CONCLUSIONS

Both the novel response formula and the nested vector-borne disease structure offer a flexible framework that can be applied to other vector-borne diseases in assessing the role of this newly identified aspect of biting behavioural ecology.

Microsatellite and mini-exon analysis of Mexican human DTU I Trypanosoma cruzi strains and their susceptibility to nifurtimox and benznidazole

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi, and it affects as many as 10 million people in North and South America, where it represents a major public health problem. T. cruzi is a parasite with high genetic diversity, and it has been grouped into 6 discrete typing units (DTUs), designated as T. cruzi I (TcI) to T. cruzi VI (TcVI). Mexican isolates from humans and from vector insects have been primarily found to be TcI, and these isolates are likely to be the strains that cause the clinical manifestations observed in Mexico. However, genetic characterization and drug susceptibility assays are limited in Mexican TcI strains. In this work, 24 Mexican T. cruzi strains, obtained primarily from humans, were studied with 7 locus microsatellites and mini-exon gene by PCR. Also, drug susceptibility was evaluated by growth and mobility assays. All of the human strains belonged to TcI, and they could be further grouped through microsatellite analysis into 2 subgroups (microsatellite genotypes 1 and 2), which were not related to the host clinical status or biological origin of the strain. Two strains, both from wild mammals, belonged to the TcII-TcVI groups; these strains and the CL Brener strain constituted microsatellite genotype 3. The number of alleles in each locus was lower than reported for South American strains, and a departure from the Hardy-Weinberg equilibrium was observed. The susceptibility of these strains to nifurtimox and benznidazole was heterogeneous. T. cruzi strains characterized as microsatellite genotypes 2 and 3 were significantly more susceptible to benznidazole than strains of microsatellite genotype 1. Only 1 Mexican strain resistant to both drugs was found in this study.

Trypanosoma cruzi I-III in southern Brazil causing individual and mixed infections in humans, sylvatic reservoirs and triatomines

The aim of this study was to characterise Discrete Typing Units (DTUs) of 28 isolates of Trypanosoma cruzi from humans (15), triatomines (9), and opossums (4) in the state of Paraná, southern Brazil. For this purpose, we analysed the size polymorphism at the 3' end of the 24Sα ribosomal RNA gene (rRNA) and the restriction fragment length polymorphism (RFLP) of the partial 5' sequence of the mitochondrial Cytochrome Oxidase subunit II gene (COII). Band patterns of the isolates were compared with reference samples of T. cruzi I (Silvio X10 and Col 17G2), T. cruzi II (Esmeraldo and JG), T. cruzi III (222 and 231), T. cruzi IV (CAN III), T. cruzi V (SO3 cl5), and T. cruzi VI (CL Brener). Our results confirmed that rRNA analysis is of limited use for assessing T. cruzi DTUs. COII RFLP analysis was suitable for screening, but for one isolate it was necessary to determine the COII partial sequence to identify the DTU. Only one of the isolates from humans belonged to T. cruzi I; 13 isolates belonged to T. cruzi II and one to T. cruzi III. The four isolates from opossums and five isolates from triatomines were identified as T. cruzi I. Four isolates from triatomines showed patterns of both T. cruzi I and II, indicating mixed infections. This study contributes to the characterisation of the dynamics of T. cruzi populations in southern Brazil.

Probing population dynamics of Trypanosoma cruzi during progression of the chronic phase in chagasic patients

Our research aimed to characterize the genetic profiles of 102 Trypanosoma cruzi isolates recently obtained from 44 chronic chagasic patients from different regions of the states of Minas Gerais and Goiás in Brazil. At least two isolates were obtained from each patient at different times in order to study the parasite population dynamics during disease progression in the chronic phase. The isolates were characterized molecularly by genotyping the 3' region of the 24S alpha rRNA, the mitochondrial cytochrome oxidase subunit 2 (COII) gene, and the intergenic region of the spliced leader intergenic region (SL-IR) gene. Seventy-seven isolates were analyzed for nine microsatellite loci. The data presented here show a strong correlation between the T. cruzi lineage II (T. cruzi II) and human infection in these regions of Brazil. Interestingly, isolates from two patients were initially characterized (by rRNA genotyping) as T. cruzi I and hybrid strains, but subsequent analyses of the COII and SL-IR genes confirmed that those isolates belonged to T. cruzi III and a hybrid group, respectively. Our results confirm the risk of misclassifying T. cruzi isolates on the basis of analysis of a single molecular marker. The microsatellite profiles showed that different isolates obtained from the same patient were genetically identical and monoclonal. Exceptions were observed for T. cruzi isolates from two patients who presented differences for the SCLE11 locus and also from two other patients who showed amplification of three peaks for a microsatellite locus (TcAAAT6), implying that they were multiclonal. On the basis of the findings of the studies described here, we were not able to establish a correlation between the clinical forms of Chagas' disease and the genetic profiles of the T. cruzi isolates.

kDNA gene signatures of Trypanosoma cruzi in blood and oesophageal mucosa from chronic chagasic patients

Trypanosoma cruzi presents a high degree of intraspecific variability, with possible implications for the pathogenesis of Chagas disease. The aim of this study was to evaluate T. cruzi kDNA minicircle gene signatures using the low-stringency single-specific-primer PCR technique in both peripheral blood and oesophageal mucosa from chronic chagasic patients, with or without megaesophagus, alone or in combination with cardiopathy and megacolon. It was not possible to identify a uniform pattern of shared bands between blood and oesophageal mucosa samples from individuals with the same clinical form or mixed forms, suggesting multiple T. cruzi infections with differential tissue tropism. Thus, the results indicate that there is an intense intraspecific variability in the hypervariable regions of T. cruzi kDNA, which has so far made it impossible to correlate the genetic profile of this structure with the clinical manifestations of Chagas disease.

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.

Random amplified polymorphic DNA profiles of Trypanosoma cruzi isolates from chagasic patients with different clinical forms

The genetic variability of 61 Trypanosoma cruzi isolates from 47 chronic chagasic patients of Minas Gerais state was analyzed by random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) using M13-40, lambdagt11-F, and L15996 primers. Cluster analysis by unweighted pair group method analysis was applied to RAPD profiles, and cluster analysis used to verify a possible correlation among different clinical forms of the disease from these patients. The T. cruzi isolates showed distinct grouping on tree topology, with the isolates not being possible to establish a correlation to the clinical forms of Chagas' disease. These data showed that the T. cruzi isolates from these patients would compose a group of populations well correlated genetically.

Trypanosoma cruzi: Two genetic groups in Paraná state, Southern Brazil

This paper presents the genetic characterization of Trypanosoma cruzi strains isolated from chronic chagasic patients, triatomines, and sylvatic reservoirs from Paraná state, Southern Brazil, using the RAPD and SSR-PCR techniques. It has shown the presence of both phylogenetic groups of T. cruzi (I and II), describing for the first time the existence of T. cruzi II in Paraná state.