Transferability of Trypanosoma cruzi from mixed human host infection to Triatoma infestans and from insects to axenic culture

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.

Discrete Typing Units of Trypanosoma cruzi Identified by Real-Time PCR in Peripheral Blood and Dejections of Triatoma infestans Used in Xenodiagnosis Descriptive Study

Chagas disease (ChD) is a vector zoonosis native to the American continent caused by the protozoan parasite Trypanosoma cruzi; the biological vectors are multiple species of hematophagous insects of the family Triatominae. A relevant aspect in the host–parasite relationship is the identification of the various genotypes of T. cruzi called discrete typing units (DTU) that circulate in mammals and vectors. In Chile, it has been described that the DTUs TcI, TcII, TcV, and TcVI circulate in infected humans, vectors, and wild animals. Identifying DTUs has acquired clinical importance, since it has been suggested that different genotypes could cause distinct pathologies, circulate in different geographical areas, and present different sensitivities to trypanocidal drugs. In this study, circulating T. cruzi DTUs in peripheral blood and Triatoma infestans dejections used in xenodiagnosis (XD) were amplified by qPCR in 14 Chilean patients with chronic ChD from highly endemic areas. More positive samples were detected by XD compared to peripheral blood samples, and 64.28% of the cases were simple infections and 35.72% mixed, with a statistically significant difference in the frequency of TcV DTU. This study would suggest that T. infestans from Chile is more competent to amplify one DTU over others, probably due to a process of co-evolution.

Biological and Genetic Heterogeneity in Trypanosoma dionisii Isolates from Hematophagous and Insectivorous Bats

This study describes the morphological, biochemical, and molecular differences among Trypanosoma dionisii isolates from hemocultures of hematophagous (Desmodus rotundus; n = 2) and insectivorous (Lonchorhina aurita; n = 1) bats from the Atlantic Rainforest of Rio de Janeiro, Brazil. Fusiform epimastigotes from the hematophagous isolates were elongated, whereas those of the insectivorous isolate were stumpy, reflected in statistically evident differences in the cell body and flagellum lengths. In the hemocultures, a higher percentage of trypomastigote forms (60%) was observed in the hematophagous bat isolates than that in the isolate from the insectivorous bat (4%), which demonstrated globular morphology. Three molecular DNA regions were analyzed: V7V8 (18S rDNA), glycosomal glyceraldehyde 3-phosphate dehydrogenase gene, and mitochondrial cytochrome b gene. The samples were also subjected to multilocus enzyme electrophoresis and random amplified polymorphic DNA analysis. All isolates were identified as T. dionisii by phylogenetic analysis. These sequences were clustered into two separate subgroups with high bootstrap values according to the feeding habits of the bats from which the parasites were isolated. However, other T. dionisii samples from bats with different feeding habits were found in the same branch. These results support the separation of the three isolates into two subgroups, demonstrating that different subpopulations of T. dionisii circulate among bats.

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.

Chagas Disease in the United States: a Public Health Approach

Trypanosoma cruzi is the etiological agent of Chagas disease, usually transmitted by triatomine vectors. An estimated 20 to 30% of infected individuals develop potentially lethal cardiac or gastrointestinal disease. Sylvatic transmission cycles exist in the southern United States, involving 11 triatomine vector species and infected mammals such as rodents, opossums, and dogs. Nevertheless, imported chronic T. cruzi infections in migrants from Latin America vastly outnumber locally acquired human cases. Benznidazole is now FDA approved, and clinical and public health efforts are under way by researchers and health departments in a number of states. Making progress will require efforts to improve awareness among providers and patients, data on diagnostic test performance and expanded availability of confirmatory testing, and evidence-based strategies to improve access to appropriate management of Chagas disease in the United States.

Chronic Chagas disease: Quantification of Trypanosoma cruzi in peripheral blood and dejections of Triatoma infestans fed by xenodiagnosis in patients with and without cardiopathy

It is not currently known which individuals with chronic Chagas disease (ChD) will develop cardiopathy in a determined period and which will be maintained asymptomatic with normal routine laboratory tests all their lives. The parasite burden is a factor that could explain this different evolution. The objective of this study was to quantify Trypanosoma cruzi burden by real-time PCR in blood (qPCR-B) and dejections of triatomines fed by xenodiagnosis (qPCR-XD) in 90 individuals with chronic ChD untreated, classified according to XD results and the presence or absence of cardiopathy. All individuals came from hyperendemic areas of Chile and participated in the study under Informed Consent. The standard qPCR curves for qPCR-B and qPCR-XD were elaborated with a mixture of known concentrations of T. cruzi strains, performing DNA serial dilutions (1/10) with a dynamic range between 10⁵ and 10^-1 parasite equivalents/mL. The TaqMan^Ⓡ detection system was applied in a Stratagene Mx3000P thermocycler (Agilent Technologies, USA) with cruzi 1 and cruzi 2 satellite primers. 22.2% and 15.6% of cases with cardiopathy or without cardiopathy were XD positive. There was no significant difference between the groups. The positivity of qPCR-B and qPCR-XD in the positive XD group was 82.35% and 100%, respectively, while in the negative XD group was 55.26% and 42.10%, respectively. A superior qPCR value in chronic ChD patients with and without cardiopathy was determined for qPCR in cases with positive XD and positive qPCR-XD. The receiver operating characteristic (ROC) curve analyses show better accuracy for detecting parasite burden (area under the curve, AUC) for qPCR-XD in comparison to qPCR-B. That is to say, major performance in DNA samples obtained of positive XD (gold standard for viable T. cruzi) detected and quantified by qPCR-XD. A high percentage of cases with XD and qPCR-XD positive (80-100%) have result concordant with qPCR-B. In absence of XD, future challenges are especially related to the low parasitic load of chronic ChD patients treated with trypanocidal drugs and post-therapy parasitological evaluations by qPCR-B. Finally, no statistically significant differences were found between presence or absence of cardiopathy and XD, qPCR-B or qPCR-XD.

Trypanosoma cruzi genetic diversity: Something new for something known about Chagas disease manifestations, serodiagnosis and drug sensitivity

The genetic diversity of Trypanosoma cruzi, the protozoan agent of Chagas disease, is widely recognized. At present, T. cruzi is partitioned into seven discrete typing units (DTUs), TcI-TcVI and Tcbat. This article reviews the present knowledge on the parasite population structure, the evolutionary relationships among DTUs and their distinct, but not exclusive ecological and epidemiological associations. Different models for the origin of hybrid DTUs are examined, which agree that genetic exchange among T. cruzi populations is frequent and has contributed to the present parasite population structure. The geographic distribution of the prevalent DTUs in humans from the southern United States to Argentina is here presented and the circumstantial evidence of a possible association between T. cruzi genotype and Chagas disease manifestations is discussed. The available information suggests that parasite strains detected in patients, regardless of the clinical presentation, reflect the principal DTU circulating in the domestic transmission cycles of a particular region. In contrast, in several orally transmitted outbreaks, sylvatic strains are implicated. As a consequence of the genotypic and phenotypic differences of T. cruzi strains and the differential geographic distribution of DTUs in humans, regional variations in the sensitivity of the serological tests are verified. The natural resistance to benznidazole and nifurtimox, verified in vivo and in vitro for some parasite stocks, is not associated with any particular DTU, and does not explain the marked difference in the anti-parasitic efficacy of both drugs in the acute and chronic phases of Chagas disease. Throughout this review, it is emphasized that the interplay between parasite and host genetics should have an important role in the definition of Chagas disease pathogenesis, anti-T. cruzi immune response and chemotherapy outcome and should be considered in future investigations.

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.

Epidemiological modeling of Trypanosoma cruzi: Low stercorarian transmission and failure of host adaptive immunity explain the frequency of mixed infections in humans

People living in areas with active vector-borne transmission of Chagas disease have multiple contacts with its causative agent, Trypanosoma cruzi. Reinfections by T. cruzi are possible at least in animal models leading to lower or even hardly detectable parasitaemia. In humans, although reinfections are thought to have major public health implications by increasing the risk of chronic manifestations of the disease, there is little quantitative knowledge about their frequency and the timing of parasite re-inoculation in the course of the disease. Here, we implemented stochastic agent-based models i) to estimate the rate of re-inoculation in humans and ii) to assess how frequent are reinfections during the acute and chronic stages of the disease according to alternative hypotheses on the adaptive immune response following a primary infection. By using a hybrid genetic algorithm, the models were fitted to epidemiological data of Argentinean rural villages where mixed infections by different genotypes of T. cruzi reach 56% in humans. To explain this percentage, the best model predicted 0.032 (0.008-0.042) annual reinfections per individual with 98.4% of them occurring in the chronic phase. In addition, the parasite escapes to the adaptive immune response mounted after the primary infection in at least 20% of the events of re-inoculation. With these low annual rates, the risks of reinfection during the typically long chronic stage of the disease stand around 14% (4%-18%) and 60% (21%-70%) after 5 and 30 years, with most individuals being re-infected 1-3 times overall. These low rates are better explained by the weak efficiency of the stercorarian mode of transmission than a highly efficient adaptive immune response. Those estimates are of particular interest for vaccine development and for our understanding of the higher risk of chronic disease manifestations suffered by infected people living in endemic areas.

Quantification by real-time PCR of Trypanosoma cruzi DNA in samples of Triatoma infestans used in xenodiagnosis of chronic Chagas disease patients

BACKGROUND

Trypanosoma cruzi multiplies and differentiates in the digestive tract of triatomine insects. Xenodiagnosis (XD) is a parasitological tool in which the insect vectors acts as a biological culture medium to amplify and detect T. cruzi infection in mammals. The sensitivity of XD has been overcome by the application of PCR in fecal samples (FS) of XD (PCR-XD). In this study, T. cruzi amplified in Triatoma infestans fed by XD on individuals with chronic Chagas disease (CChD) is quantified by real-time PCR (qPCR-XD).

FINDINGS

Under informed consent, 100 individuals were evaluated. In 21 of them XD, PCR-XD and qPCR-XD were positive. For the contrary, 79 were negative XD. In 58 (73.4 %) and 66 cases (83.5 %) of them, PCR-XD (Fisher's exact test P = 0.005) and qPCR-XD (Fisher's exact test: P = 0.037) respectively, were positive. In cases with positive XD, qPCR-XD allowed to establish that in 9/21 cases (42.9 %) the parasite burden fluctuated between 100 and 1,000 par. eq./ml. Otherwise, in 32/79 (40.5 %) cases with negative XD, a parasite burden between 1 and 10 par. eq./ml was determined. All samples showed amplification of exogenous internal control (X12, Ct average: 31.8), so problems in the DNA extraction (excess or loss of genetic material), unspecific amplification and/or inhibition in qPCR-XD reactions were ruled out. Additionally, in all the patients qPCR in blood (qPCR-B) was performed. In the cases with positive XD, the concordance between the positivity of qPCR-XD and qPCR-B was 100 %, nevertheless, the parasite burden in blood was lower and different than XD (Chi-square test: χ (2)  = 91.82, df = 5, P = 0.0001). In the cases with negative XD the ranges of qPCR-XD and qPCR-B were similar (Chi-square test: χ (2)  = 6.71, df = 5, P = 0.1520).

CONCLUSIONS

This study allowed the detection and quantification of T. cruzi by qPCR-XD in FS of Tr. infestans fed on patients with CChD. The highest parasite burden was observed in positive XD cases. qPCR-XD could be used in different studies related with the complex T. cruzi-vector-host interactions.

Complexity and multi-factoriality of Trypanosoma cruzi sylvatic cycle in coatis, Nasua nasua (Procyonidae), and triatomine bugs in the Brazilian Pantanal

Background

Trypanosoma cruzi is dispersed in nature through many transmission mechanisms among a high diversity of vectors and mammalian species, representing particular behaviors and habitats. Thus, each locality has a unique set of conditions underlying the maintenance of this parasite in the wild. The aim of the present study was to evaluate the life-cycle of T. cruzi in free-ranging coatis from the central region of the Brazilian Pantanal using a multi-factorial approach.

Methods

Three methodological blocks were used in the present study: (i) We evaluated T. cruzi infection using serological (ELISA) and parasitological (hemoculture) tests in free-ranging coatis captured from October 2010 to March 2012. In addition, we characterized T. cruzi isolates as DTUs (Discrete Typing Units); (ii) We evaluated Trypanosoma infection in species of Triatoma and Rhodnius inhabiting coati arboreal nests from May to September 2012 using parasitological and molecular assays; and (iii) We analyzed a set of longitudinal data (from 2005 to 2012) concerning the effects of T. cruzi infection on this coati population. Herein, we investigated whether seasonality, host sex, and host age influence T. cruzi prevalence and patterns of infection.

Results

The 2010–2012 period presented high seroprevalence on coatis (72.0 % ELISA) and a high percentage of individuals with infectivity competence (20.5 % positive hemoculture). All isolates presented TcI band patterns, occurring in single (n = 3) and mixed infections (1 TcI/T. rangeli; 4 with undefined characterization). Both male and female individuals presented the same transmission potential, expressed as positive hemoculture, which was only detected in the summer. However, overall, the data (2005–2012) highlighted the importance of females for T. cruzi maintenance in the winter. Moreover, twenty-three (67.6 %) bugs from five coati nests (71.4 %) were infected with flagellated forms. Seventeen samples were characterized as T. cruzi (TcI and TcIII genotypes).

Conclusion

In the Pantanal region, T. cruzi is transmitted in a complex, multifactorial, dynamic and non-linear transmission web. The coati nests might be inserted in this web, acting as important transmission foci at the arboreal stratum to different mammal species with arboreal or scansorial behavior.

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.