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

New insights into Trypanosoma cruzi genetic diversity, and its influence on parasite biology and clinical outcomes

Chagas disease, caused by Trypanosoma cruzi, remains a serious public health problem worldwide. The parasite was subdivided into six distinct genetic groups, called "discrete typing units" (DTUs), from TcI to TcVI. Several studies have indicated that the heterogeneity of T. cruzi species directly affects the diversity of clinical manifestations of Chagas disease, control, diagnosis performance, and susceptibility to treatment. Thus, this review aims to describe how T. cruzi genetic diversity influences the biology of the parasite and/or clinical parameters in humans. Regarding the geographic dispersion of T. cruzi, evident differences were observed in the distribution of DTUs in distinct areas. For example, TcII is the main DTU detected in Brazilian patients from the central and southeastern regions, where there are also registers of TcVI as a secondary T. cruzi DTU. An important aspect observed in previous studies is that the genetic variability of T. cruzi can impact parasite infectivity, reproduction, and differentiation in the vectors. It has been proposed that T. cruzi DTU influences the host immune response and affects disease progression. Genetic aspects of the parasite play an important role in determining which host tissues will be infected, thus heavily influencing Chagas disease's pathogenesis. Several teams have investigated the correlation between T. cruzi DTU and the reactivation of Chagas disease. In agreement with these data, it is reasonable to suppose that the immunological condition of the patient, whether or not associated with the reactivation of the T. cruzi infection and the parasite strain, may have an important role in the pathogenesis of Chagas disease. In this context, understanding the genetics of T. cruzi and its biological and clinical implications will provide new knowledge that may contribute to additional strategies in the diagnosis and clinical outcome follow-up of patients with Chagas disease, in addition to the reactivation of immunocompromised patients infected with T. cruzi.

Human Chagas-Flow ATE-IgG1 for advanced universal and Trypanosoma cruzi Discrete Typing Units-specific serodiagnosis of Chagas disease

The molecular and serological methods available for Discrete Typing Units (DTU)-specific diagnosis of Trypanosoma cruzi in chronic Chagas disease present limitations. The study evaluated the performance of Human Chagas-Flow ATE-IgG1 for universal and DTU-specific diagnosis of Chagas disease. A total of 102 sera from Chagas disease patients (CH) chronically infected with TcI, TcVI or TcII DTUs were tested for IgG1 reactivity to amastigote/(A), trypomastigote/(T) and epimastigote/(E) antigens along the titration curve (1:250-1:32,000). The results demonstrated that "AI 250/40%", "EVI 250/30%", "AII 250/40%", "TII 250/40%" and "EII 250/30%" have outstanding accuracy (100%) to segregate CH from non-infected controls. The attributes "TI 4,000/50%", "EI 2,000/50%", "AVI 8,000/60%" and "TVI 4,000/50%" were selected for DTU-specific serotyping of Chagas disease. The isolated use of "EI 2,000/50%" provided the highest co-positivity for TcI patients (91%). The combined decision tree algorithms using the pre-defined sets of attributes showed outstanding full accuracy (92% and 97%) to discriminate "TcI vs TcVI vs TcII" and "TcI vs TcII" prototypes, respectively. The elevated performance of Human Chagas-Flow ATE-IgG1 qualifies its use for universal and TcI/TcVI/TcII-specific diagnosis of Chagas disease. These findings further support the application of this method in epidemiological surveys, post-therapeutic monitoring and clinical outcome follow-ups for Chagas disease.

Accomplishing the genotype-specific serodiagnosis of single and dual Trypanosoma cruzi infections by flow cytometry Chagas-Flow ATE-IgG2a

The methods currently available for genotype-specific diagnosis of T. cruzi infection still present relevant limitations, especially to identify mixed infection. In the present investigation, we have evaluated the performance of Chagas-Flow ATE-IgG2a test for early and late differential diagnosis of single and dual genotype-specific T. cruzi infections. Serum samples from Swiss mice at early and late stages of T. cruzi infection were assayed in parallel batches for genotype-specific diagnosis of single (TcI, TcVI or TcII) and dual (TcI+TcVI, TcVI+TcII or TcII+TcI) infections. The intrinsic reactivity to TcI, TcVI and TcII target antigens, including amastigote (AI/AVI/AII), trypomastigote-(TI/TVI/TII) and epimastigote (EI/EVI/EII), at specific reverse of serum dilutions (500 to 64,000), was employed to provide reliable decision-trees for "early" vs "late", "single vs "dual" and "genotype-specific" serology. The results demonstrated that selective set of attributes "EII 500/EI 2,000/AII 500" were able to provide high-quality accuracy (81%) to segregate early and late stages of T. cruzi infection. The sets "TI 2,000/AI 1,000/EII 1,000" and "TI 8,000/AII 32,000" presented expressive scores to discriminate single from dual T. cruzi infections at early (85%) and late stages (84%), respectively. Moreover, the attributes "TI 4,000/TVI 500/TII 1,000", "TI 16,000/EI 2,000/EII 2,000/AI 500/TVI 500" showed good performance for genotype-specific diagnosis at early stage of single (72%) and dual (80%) T. cruzi infections, respectively. In addition, the attributes "TI 4,000/AII 1,000/EVI 1,000", "TI 64,000/AVI 500/AI 2,000/AII 1,000/EII 4,000" showed moderate performance for genotype-specific diagnosis at late stage of single (69%) and dual (76%) T. cruzi infections, respectively. The sets of decision-trees were assembled to construct a sequential algorithm with expressive accuracy (81%) for serological diagnosis of T. cruzi infection. These findings engender new perspectives for the application of Chagas-Flow ATE-IgG2a method for genotype-specific diagnosis in humans, with relevant contributions for epidemiological surveys as well as clinical and post-therapeutic monitoring of Chagas disease.

The effect of reinfection and mixed Trypanosoma cruzi infections on disease progression in mice

The progression of Chagas disease (CD) varies significantly from host to host and is affected by multiple factors. In particular, mixed strain infections and reinfections have the potential to exacerbate disease progression subsequently affecting clinical management of patients with CD. Consequently, an associated reduction in therapeutic intervention and poor prognosis may occur due to this exacerbated disease state. This study investigated the effects of mixed strain infections and reinfection with Trypanosoma cruzi in mice, using two isolates from different discrete typing units, TcI (C8 clone 1) and TcIV (10R26). There were no significant differences in mortality rate, body weight or body condition among mice infected with either C8 clone 1, 10R26, or a mixture of both isolates. However, the parasite was found in a significantly greater number of host organs in mice infected with a mixture of isolates, and the histopathological response to infection was significantly greater in mice infected with C8 clone 1 alone, and C8 clone 1+10R26 mixed infections than in mice infected with 10R26 alone. To investigate the effects of reinfection, mice received either a double exposure to C8 clone 1; a double exposure to 10R26; exposure to C8 clone 1 followed by 10R26; or exposure to 10R26 followed by C8 clone 1. Compared to single infection groups, mortality was significantly increased, while survival time, body weight and body condition were all significantly decreased across all reinfection groups, with no significant differences among these groups. The mortality rate over all reinfection groups was 63.6%, compared to 0% in single infection groups, however there was no evidence of a greater histopathological response to infection. These results suggest firstly, that the C8 clone 1 isolate is more virulent than the 10R26 isolate, and secondly, that a more disseminated infection may occur with a mixture of isolates than with single isolates, although there is no evidence that mixed infections have a greater pathological effect. By contrast, reinfections do have major effects on host survivability and thus disease outcome. This confirms previous research demonstrating spontaneous deaths following reinfection, a phenomenon that to our knowledge has only been reported once before.

TcI, TcII and TcVI Trypanosoma cruzi samples from Chagas disease patients with distinct clinical forms and critical analysis of in vitro and in vivo behavior, response to treatment and infection evolution in murine model

The clonal evolution of Trypanosoma cruzi sustains scientifically the hypothesis of association between parasite's genetic, biological behavior and possibly the clinical aspects of Chagas disease in patients from whom they were isolated. This study intended to characterize a range of biological properties of TcI, TcII and TcVI T. cruzi samples in order to verify the existence of these associations. Several biological features were evaluated, including in vitro epimastigote-growth, "Vero"cells infectivity and growth, along with in vivo studies of parasitemia, polymorphism of trypomastigotes, cardiac inflammation, fibrosis and response to treatment by nifurtimox during the acute and chronic murine infection. The global results showed that the in vitro essays (acellular and cellular cultures) TcII parasites showed higher values for all parameters (growth and infectivity) than TcVI, followed by TcI. In vivo TcII parasites were more virulent and originated from patients with severe disease. Two TcII isolates from patients with severe pathology were virulent in mice, while the isolate from a patient with the indeterminate form of the disease caused mild infection. The only TcVI sample, which displayed low values in all parameters evaluated, was also originated of an indeterminate case of Chagas disease. Response to nifurtimox was not associated to parasite genetic and biology, as well as to clinical aspects of human disease. Although few number of T. cruzi samples have been analyzed, a discreet correlation between parasite genetics, biological behavior in vitro and in vivo (murine model) and the clinical form of human disease from whom the samples were isolated was verified.

Between a bug and a hard place: Trypanosoma cruzi genetic diversity and the clinical outcomes of Chagas disease

Over the last 30 years, concomitant with successful transnational disease control programs across Latin America, Chagas disease has expanded from a neglected, endemic parasitic infection of the rural poor to an urbanized chronic disease, and now a potentially emergent global health problem. Trypanosoma cruzi infection has a highly variable clinical course, ranging from complete absence of symptoms to severe and often fatal cardiovascular and/or gastrointestinal manifestations. To date, few correlates of clinical disease progression have been identified. Elucidating a putative role for T. cruzi strain diversity in Chagas disease pathogenesis is complicated by the scarcity of parasites in clinical specimens and the limitations of our contemporary genotyping techniques. This article systematically reviews the historical literature, given our current understanding of parasite genetic diversity, to evaluate the evidence for any association between T. cruzi genotype and chronic clinical outcome, risk of congenital transmission or reactivation and orally transmitted outbreaks.

Effects of artesunate against Trypanosma cruzi

Therapy against Trypanosma cruzi relies on only two chemically related nitro-derivative drugs, benznidazole and nifurtimox, both limited by poor efficacy and toxicity. It is suspected that with prolonged usage of these drugs, resistant parasites will be selected, which results in risk for treatment failure over the time. Herein, we studied the in vitro activity of artesunate, the most effective drug to treat severe P. falciparum and chloroquine-resistant P. vivax, on three strains of T. cruzi originated in different regions of Latin America (Argentina, Nicaragua and Brazil). The results of these assays showed that artesunate inhibits multiplication of epimastigotes (IC50 = 50, 6.10 and 23 µM, respectively) and intracellular amastigotes (IC50 = 15, 0.12 and 6.90 µM, respectively), indicating that it represents a potent anti-T. cruzi compound in terms of inhibiting parasite multiplication in vitro. We then tested the effect of artesunate in Balb/c mice infected with Brazil strain and found that it failed to cure the infection, suggesting that the drug may be unsuitable for in vivo treatment. When infected mice were treated with high doses AS + BZ, the outcome of infection was similar to that observed in mice treated with BZ alone. Nevertheless, understanding of structure-activity relationship of artesunate might lead to the development of new and effective drugs against T. cruzi.

Are Members of the Triatoma brasiliensis (Hemiptera, Reduviidae) Species Complex Able to Alter the Biology and Virulence of a Trypanosoma cruzi Strain?

Trypanosoma cruzi is the causative agent of Chagas disease, transmitted to humans and mammals by blood-sucking hemipteran insects belonging to the Triatominae subfamily. The two main genotypes of T. cruzi (TcI and TcII) differ in many characteristics concerning their genetic profile. Despite the extensive literature on vectors and the etiologic agent, several interactive aspects between these two elements of Chagas disease are still waiting to be further clarified. Here, biological and histological features resulting from the interaction between Albino Swiss mice and T. cruzi isolate PB913 after passages through vectors of the Triatoma brasiliensis species complex were evaluated. Comparing the four members of the T. brasiliensis species complex-Triatoma brasiliensis brasiliensis Neiva, Triatoma brasiliensis macromelasoma Galvão, Triatoma melanica Neiva & Lent, and Triatoma juazeirensis Costa & Felix-no significant differences in parasitemia of the infected mice were observed. At 20 days post-infection, the highest number of parasites was observed in the group of mice that were infected with parasites obtained from T. b. macromelasoma. Tropism of the parasites to different organs such as heart, bladder, and skeletal muscles followed by inflammatory cell infiltrates was observed with quantitative and qualitative differences. Even though the four members of the T. brasiliensis species complex differ in their geographical distribution, morphology, biology, ecology, and genetics, no significant influence on the parasitemia of the T. cruzi PB913 isolate was detected. After evaluation of the tissue samples, a higher pathogenicity of parasites obtained from T. b. brasiliensis was noticeable.

Experimental evidence of biological interactions among different isolates of Trypanosoma cruzi from the Chaco Region

Many infectious diseases arise from co-infections or re-infections with more than one genotype of the same pathogen. These mixed infections could alter host fitness, the severity of symptoms, success in pathogen transmission and the epidemiology of the disease. Trypanosoma cruzi, the etiological agent of Chagas disease, exhibits a high biological variability often correlated with its genetic diversity. Here, we developed an experimental approach in order to evaluate biological interaction between three T. cruzi isolates belonging to different Discrete Typing Units (DTUs TcIII, TcV and TcVI). These isolates were obtained from a restricted geographical area in the Chaco Region. Different mixed infections involving combinations of two isolates (TcIII + TcV, TcIII + TcVI and TcV + TcVI) were studied in a mouse model. The parameters evaluated were number of parasites circulating in peripheral blood, histopathology and genetic characterization of each DTU in different tissues by DNA hybridization probes. We found a predominance of TcVI isolate in blood and tissues respect to TcIII and TcV; and a decrease of the inflammatory response in heart when the damage of mice infected with TcVI and TcIII + TcVI mixture were compared. In addition, simultaneous presence of two isolates in the same tissue was not detected. Our results show that biological interactions between isolates with different biological behaviors lead to changes in their biological properties. The occurrence of interactions among different genotypes of T. cruzi observed in our mouse model suggests that these phenomena could also occur in natural cycles in the Chaco Region.

Circulating Trypanosoma cruzi populations differ from those found in the tissues of the same host during acute experimental infection

We evaluated the presence and distribution of two Trypanosoma cruzi natural isolates in blood, heart, skeletal muscle, liver, and spleen tissues in the acute phase of the experimental infection (35 days postinfection) in order to determine if the populations present in blood were different to those found in the tissues of the same host. Thirty mice were infected with 50 forms of each isolate or with a combination of them. Presence and molecular characterization of the parasites in the host tissues were determined by specific PCR. Cardiac and skeletal muscle alterations were analyzed by histological studies. T. cruzi variability in the host tissues was analyzed through RFLP studies. Both isolates used consisted of a mixture of two T. cruzi lineages. Specific PCRs were positive for most of the samples from the 3 groups analyzed. Cardiac and skeletal muscle sections from the groups infected with one isolate presented mild to moderate inflammatory infiltrates; the group infected with both isolates showed severe inflammatory infiltrates and the presence of amastigote nests in both tissues. Different parasite populations were found in circulation and in the tissues from the same host. These results are important for patients with high probability of mixed infections in endemic areas and contribute to the knowledge of parasite/host interactions.

Genetic modulation in Be-78 and Y Trypanosoma cruzi strains after long-term infection in Beagle dogs revealed by molecular markers

The genetic profile of Trypanosoma cruzi was evaluated in parasite populations isolated from Beagle dogs experimentally infected with Be-78 and Y strains that present distinct biological and genetic characteristics. Molecular characterization of the isolates obtained 30days and 2years after infection was carried out. For typing MLEE, sequence polymorphisms of the mitochondrial cytochrome oxidase subunit II gene (COII) and RAPD profiles were used. The profiles of MLEE were the same for the parental Be-78 strains as their respective isolates. However, changes of MLEE profile were observed in two T. cruzi isolates from dogs inoculated with Y strain. Changes in the mitochondrial DNA (COII) and RAPD profiles of the Y strain were also observed. The dendogram constructed by UPGMA with RAPD results indicated two major branches. Global data show that the genetic modulation in polyclonal strains during the long-term infection occurred and was strain-dependent. This study still suggests that each host (here each dog) harbors a determinate T. cruzi population that may change or be modulated throughout long-term infection. This might to hinder the observation of correlation between the genetics of T. cruzi and their biological properties and behavior in different host species due to the complexity of the parasite-host interaction in which probably the genetic background of both should be considered.

Coinfection with different Trypanosoma cruzi strains interferes with the host immune response to infection

A century after the discovery of Trypanosoma cruzi in a child living in Lassance, Minas Gerais, Brazil in 1909, many uncertainties remain with respect to factors determining the pathogenesis of Chagas disease (CD). Herein, we simultaneously investigate the contribution of both host and parasite factors during acute phase of infection in BALB/c mice infected with the JG and/or CL Brener T. cruzi strains. JG single infected mice presented reduced parasitemia and heart parasitism, no mortality, levels of pro-inflammatory mediators (TNF-α, CCL2, IL-6 and IFN-γ) similar to those found among naïve animals and no clinical manifestations of disease. On the other hand, CL Brener single infected mice presented higher parasitemia and heart parasitism, as well as an increased systemic release of pro-inflammatory mediators and higher mortality probably due to a toxic shock-like systemic inflammatory response. Interestingly, coinfection with JG and CL Brener strains resulted in intermediate parasitemia, heart parasitism and mortality. This was accompanied by an increase in the systemic release of IL-10 with a parallel increase in the number of MAC-3(+) and CD4(+) T spleen cells expressing IL-10. Therefore, the endogenous production of IL-10 elicited by coinfection seems to be crucial to counterregulate the potentially lethal effects triggered by systemic release of pro-inflammatory mediators induced by CL Brener single infection. In conclusion, our results suggest that the composition of the infecting parasite population plays a role in the host response to T. cruzi in determining the severity of the disease in experimentally infected BALB/c mice. The combination of JG and CL Brener was able to trigger both protective inflammatory immunity and regulatory immune mechanisms that attenuate damage caused by inflammation and disease severity in BALB/c mice.

Genotyping of Trypanosoma cruzi sublineage in human samples from a North-East Argentina area by hybridization with DNA probes and specific polymerase chain reaction (PCR)

We have evaluated blood samples of chronic and congenital Trypanosoma cruzi-infected patients from the city of Reconquista located in the northeast of Argentina where no information was previously obtained about the genotype of infecting parasites. Fourteen samples of congenital and 19 chronical patients were analyzed by hybridization with DNA probes of minicircle hypervariable regions (mHVR). In congenital patients, 50% had single infections with TcIId, 7% single infections with TcIIe, 29% mixed infections with TcIId/e, and 7% had mixed infections with TcIId/b and 7% TcIId/b, respectively. In Chronical patients, 52% had single infections with TcIId, 11% single infections with TcIIe, 26% had mixed infections with TcIId/e, and 11% had non-identified genotypes. With these samples, we evaluated the minicircle lineage-specific polymerase chain reaction assay (MLS-PCR), which involves a nested PCR to HVR minicircle sequences and we found a correlation with hybridization probes of 96.4% for TcIId and 54.8% for TcIIe.