New human isolates of Trypanosoma cruzi confirm the predominance of hybrid lineages in domestic transmission cycle of the Argentinean Chaco

Deep serological profiling of the Trypanosoma cruzi TSSA antigen reveals different epitopes and modes of recognition by Chagas disease patients

BACKGROUND

Trypanosoma cruzi, the agent of Chagas disease, displays a highly structured population, with multiple strains that can be grouped into 6-7 evolutionary lineages showing variable eco-epidemiological traits and likely also distinct disease-associated features. Previous works have shown that antibody responses to 'isoforms' of the polymorphic parasite antigen TSSA enable robust and sensitive identification of the infecting strain with near lineage-level resolution. To optimize the serotyping performance of this molecule, we herein used a combination of immunosignaturing approaches based on peptide microarrays and serum samples from Chagas disease patients to establish a deep linear B-cell epitope profiling of TSSA.

METHODS/PRINCIPLE FINDINGS

Our assays revealed variations in the seroprevalence of TSSA isoforms among Chagas disease populations from different settings, hence strongly supporting the differential distribution of parasite lineages in domestic cycles across the Americas. Alanine scanning mutagenesis and the use of peptides of different lengths allowed us to identify key residues involved in antibody pairing and the presence of three discrete B-cell linear epitopes in TSSAII, the isoform with highest seroprevalence in human infections. Comprehensive screening of parasite genomic repositories led to the discovery of 9 novel T. cruzi TSSA variants and one TSSA sequence from the phylogenetically related bat parasite T. cruzi marinkellei. Further residue permutation analyses enabled the identification of diagnostically relevant or non-relevant substitutions among TSSA natural polymorphisms. Interestingly, T. cruzi marinkellei TSSA displayed specific serorecognition by one chronic Chagas disease patient from Colombia, which warrant further investigations on the diagnostic impact of such atypical TSSA.

CONCLUSIONS/SIGNIFICANCE

Overall, our findings shed new light into TSSA evolution, epitope landscape and modes of recognition by Chagas disease patients; and have practical implications for the design and/or evaluation of T. cruzi serotyping strategies.

Dynamics of Triatoma infestans populations in the Paraguayan Chaco: Population genetic analysis of household reinfestation following vector control

Background

Although domestic infestations by Triatoma infestans have been successfully controlled across Latin America, in areas of the Gran Chaco region, recurrent post-spraying house colonization continues to be a significant challenge, jeopardizing Chagas disease vector control and maintaining active Trypanosoma cruzi transmission.

Methodology/Principal findings

To investigate the dynamics of triatomine reinfestation in a rural area of the Paraguayan Chaco, genetic characterization (based on 10 microsatellite loci and cytochrome B sequence polymorphisms) was performed on baseline and reinfestant T. infestans (n = 138) from four indigenous communities and adjacent sylvatic sites. House quality and basic economic activities were assessed across the four communities. Significant genetic differentiation was detected among all baseline triatomine populations. Faster reinfestation was observed in the communities with higher infestation rates pre-spraying. Baseline and reinfestant populations from the same communities were not genetically different, but two potentially distinct processes of reinfestation were evident. In Campo Largo, the reinfestant population was likely founded by domestic survivor foci, with reduced genetic diversity relative to the baseline population. However, in 12 de Junio, reinfestant bugs were likely derived from different sources, including survivors from the pre-spraying population and sympatric sylvatic bugs, indicative of gene-flow between these habitats, likely driven by high human mobility and economic activities in adjacent sylvatic areas.

Conclusions/Significance

Our results demonstrate that sylvatic T. infestans threatens vector control strategies, either as a reinfestation source or by providing a temporary refuge during insecticide spraying. Passive anthropogenic importation of T. infestans and active human interactions with neighboring forested areas also played a role in recolonization. Optimization of spraying, integrated community development and close monitoring of sylvatic areas should be considered when implementing vector control activities in the Gran Chaco.

Over-dispersed Trypanosoma cruzi parasite load in sylvatic and domestic mammals and humans from northeastern Argentina

BACKGROUND

The distribution of parasite load across hosts may modify the transmission dynamics of infectious diseases. Chagas disease is caused by a multi-host protozoan, Trypanosoma cruzi, but the association between host parasitemia and infectiousness to the vector has not been studied in sylvatic mammalian hosts. We quantified T. cruzi parasite load in sylvatic mammals, modeled the association of the parasite load with infectiousness to the vector and compared these results with previous ones for local domestic hosts.

METHODS

The bloodstream parasite load in each of 28 naturally infected sylvatic mammals from six species captured in northern Argentina was assessed by quantitative PCR, and its association with infectiousness to the triatomine Triatoma infestans was evaluated, as determined by natural or artificial xenodiagnosis. These results were compared with our previous results for 88 humans, 70 dogs and 13 cats, and the degree of parasite over-dispersion was quantified and non-linear models fitted to data on host infectiousness and bloodstream parasite load.

RESULTS

The parasite loads of Didelphis albiventris (white-eared opossum) and Dasypus novemcinctus (nine-banded armadillo) were directly and significantly associated with infectiousness of the host and were up to 190-fold higher than those in domestic hosts. Parasite load was aggregated across host species, as measured by the negative binomial parameter, k, and found to be substantially higher in white-eared opossums, cats, dogs and nine-banded armadillos (range: k = 0.3-0.5) than in humans (k = 5.1). The distribution of bloodstream parasite load closely followed the "80-20 rule" in every host species examined. However, the 20% of human hosts, domestic mammals or sylvatic mammals exhibiting the highest parasite load accounted for 49, 25 and 33% of the infected triatomines, respectively.

CONCLUSIONS

Our results support the use of bloodstream parasite load as a proxy of reservoir host competence and individual transmissibility. The over-dispersed distribution of T. cruzi bloodstream load implies the existence of a fraction of highly infectious hosts that could be targeted to improve vector-borne transmission control efforts toward interruption transmission. Combined strategies that decrease the parasitemia and/or host-vector contact with these hosts would disproportionally contribute to T. cruzi transmission control.

Biological features of TcM: A new Trypanosoma cruzi isolate from Argentina classified into TcV lineage

•

TcM is a new T. cruzi isolate that belongs to DTU TcV.

•

TcV is a T. cruzi linage prevalent in human infections of Argentina.

•

TcM is less virulent that TcY strain.

•

TcM displays slow-growing rate and muscle tissue tropism.

•

TcM is more susceptible to benznidazole than TcY.

Trypanosoma cruzi, the etiologic agent of Chagas disease (CD) presents a wide genetic and phenotypic diversity that is classified into seven lineages or discrete typing units (DTU: TcI to TcVI and Tcbat). Although isolates and strains that belong to a particular group can share some attributes, such as geographic distribution, others like growth rate, cell tropism, and response to treatment can be highly variable. In addition, studies that test new trypanocidal drugs are frequently conducted on T. cruzi strains maintained for a long time in axenic culture, resulting in changes in parasite virulence and other important features. This work aimed to isolate and characterize a new T. cruzi strain from a chronic Chagas disease patient. The behavior of this isolate was studied by using standard in vitro assays and in vivo mice infection tests and compared with the T. cruzi Y strain (TcY), broadly used in research laboratories worldwide. Data showed that TcM behaves as a slow-growing strain in vitro that develops chronic infections in mice and displays high tropism to muscular tissues, in accordance with its clinical performance. In contrast, the Y strain behaved as an acute strain that can infect different types of cells and tissues. Interestingly, TcM, which belongs to DTU TcV, is more susceptible to benznidazole than TcY, a TcII strain considered moderately resistant to this drug. These differential properties contribute to the characterization of a TcV strain, one of the main lineages in the southern countries of South America, and open the possibility to introduce changes that improve the management of Chagas patients in the future

Assessing antibody decline after chemotherapy of early chronic Chagas disease patients

BACKGROUND

Chagas disease remains a significant public health problem in Latin America. There are only two chemotherapy drugs, nifurtimox and benznidazole, and both may have severe side effects. After complete chemotherapy of acute cases, seropositive diagnosis may revert to negative. However, there are no definitive parasitological or serological biomarkers of cure.

METHODS

Following a pilot study with seven Bolivian migrants to Spain, we tested 71 serum samples from chronic patients (mean age 12.6 years) inhabiting the Argentine Chaco region. Benznidazole chemotherapy (5-8 mg/kg day, twice daily for 60 days) was administered during 2011-2016. Subsequently, pre-and post-chemotherapy serum samples were analysed in pairs by IgG1 and IgG ELISA using two different antigens and Chagas Sero K-SeT rapid diagnostic tests (RDT). Molecular diagnosis by kDNA-PCR was applied to post-treatment samples.

RESULTS

Pilot data demonstrated IgG1 antibody decline in three of seven patients from Bolivia 1 year post-treatment. All Argentine patients in 2017 (averaging 5 years post-treatment), except one, were positive by conventional serology. All were kDNA-PCR-negative. Most (91.5%) pre-treatment samples were positive by the Chagas Sero K-SeT RDT, confirming the predominance of TcII/V/VI. IgG1 and IgG of Argentine patients showed significant decline in antibody titres post-chemotherapy, with either lysate (IgG, P = 0.0001, IgG1, P = 0.0001) or TcII/V/VI peptide antigen (IgG, P = 0.0001, IgG1, P = 0.0001). IgG1 decline was more discriminative than IgG. Antibody decline after treatment was also detected by the RDT. Incomplete treatment was associated with high IgG1 post-treatment titres against lysate (P = 0.013), as were IgG post-treatment titres to TcII/V/VI peptide (P = 0.0001). High pre-treatment IgG1 with lysate was associated with Qom ethnicity (P = 0.045). No associations were found between gender, age, body mass index and pre- or post-treatment antibody titres.

CONCLUSIONS

We show that following chemotherapy of early chronic Chagas disease, significant decline in IgG1 antibody suggests cure, whereas sustained or increased IgG1 is a potential indicator of treatment failure. Due to restricted sensitivity, IgG1 should not be used as a diagnostic marker but has promise, with further development, as a biomarker of cure. We show that following chemotherapy of early chronic Chagas disease, a significant decline in IgG1 antibody suggests cure, whereas sustained or increased IgG1 is a potential indicator of treatment failure. Due to restricted sensitivity, IgG1 should not be used as a diagnostic marker but has promise, with further development, as a biomarker of cure.

Intra-Discrete Typing Unit TcV Genetic Variability of Trypanosoma cruzi in Chronic Chagas' Disease Bolivian Immigrant Patients in Barcelona, Spain

Background: Trypanosoma cruzi has a high rate of biological and genetic variability, and its population structure is divided into seven distinct genetic groups (TcI-TcVI and Tcbat). Due to immigration, Chagas disease (ChD), caused by T. cruzi, has become a serious global health problem including in Europe. Therefore, the aim of this study was to evaluate the existence of genetic variability within discrete typing unit (DTU) TcV of T. cruzi in Bolivian patients with chronic ChD residing in Barcelona, Spain. Methods: The DNA was extracted from the peripheral blood of 27 patients infected with T. cruzi DTU TcV and the fragments of the genetic material were amplificated through the low stringency single primer-polymerase chain reaction (LSSP-PCR). The data generated after amplification were submitted to bioinformatics analysis. Results: Of the 27 patients evaluated in the study, 8/27 (29.6%) were male and 19/27 (70.4%) female, 17/27 (62.9%) were previously classified with the indeterminate clinical form of Chagas disease and 10/27 (37.1%) with Chagas cardiomyopathy. The LSSP-PCR detected 432 band fragments from 80 to 1,500 bp. The unweighted pair-group method analysis and principal coordinated analysis data demonstrated the existence of three distinct genetic groups with moderate-high rates of intraspecific genetic variability/diversity that had shared parasite's alleles in patients with the indeterminate and cardiomyopathy forms of ChD. Conclusions: This study demonstrated the existence of a moderate to high rate of intra-DTU TcV variability in T. cruzi. Certain alleles of the parasite were associated with the absence of clinical manifestations in patients harboring the indeterminate form of ChD. These results support the need to search for increasingly specific targets in the genome of T. cruzi to be correlated with its main biological properties and clinical features in patients with chronic ChD.

Long-term impact of a ten-year intervention program on human and canine Trypanosoma cruzi infection in the Argentine Chaco

BACKGROUND

Interruption of domestic vector-borne transmission of Trypanosoma cruzi is still an unmet goal in several American countries. In 2007 we launched a long-term intervention program aimed to suppress house infestation with the main domestic vector in southern South America (Triatoma infestans) and domestic transmission in Pampa del Indio, a resource-constrained, hyperendemic municipality with 1446 rural houses inhabited by Creole and indigenous people, in the Argentine Chaco ecoregion. Here, we assessed whether the 10-year insecticide-based program combined with community mobilization blocked vector-borne domestic transmission of T. cruzi to humans and dogs.

METHODS

We carried out two municipality-wide, cross-sectional serosurveys of humans and dogs (considered sentinel animals) during 2016-2017 to compare with baseline data. We used a risk-stratified random sampling design to select 273 study houses; 410 people from 180 households and 492 dogs from 151 houses were examined for antibodies to T. cruzi using at least two serological methods.

RESULTS

The seroprevalence of T. cruzi in children aged <16 years was 2.5% in 2017 (i.e., 4- to 11-fold lower than before interventions). The mean annual force of child infection (λ) sharply decreased from 2.18 to 0.34 per 100 person-years in 2017. One of 102 children born after interventions was seropositive for T. cruzi; he had lifetime residence in an apparently uninfested house, no outside travel history, and his mother was T. cruzi-seropositive. No incident case was detected among 114 seronegative people of all ages re-examined serologically. Dog seroprevalence was 3.05%. Among native dogs, λ in 2016 (1.21 per 100 dog-years) was 5 times lower than at program onset. Six native adult dogs born after interventions and with stable lifetime residence were T. cruzi-seropositive: three had exposure to T. infestans at their houses and one was an incident case.

CONCLUSIONS

These results support the interruption of vector-borne transmission of T. cruzi to humans in rural Pampa del Indio. Congenital transmission was the most likely source of the only seropositive child born after interventions. Residual transmission to dogs was likely related to transient infestations and other transmission routes. Sustained vector control supplemented with human chemotherapy can lead to a substantial reduction of Chagas disease transmission in the Argentine Chaco.

Serological Approaches for Trypanosoma cruzi Strain Typing

Trypanosoma cruzi, the protozoan agent of Chagas' disease, displays a complex population structure made up of multiple strains showing a diverse ecoepidemiological distribution. Parasite genetic variability may be associated with disease outcome, hence stressing the need to develop methods for T. cruzi typing in vivo. Serological typing methods that exploit the presence of host antibodies raised against polymorphic parasite antigens emerge as an appealing approach to address this issue. These techniques are robust, simple, cost-effective, and are not curtailed by methodological/biological limitations intrinsic to available genotyping methods. Here, we critically assess the progress towards T. cruzi serotyping and discuss the opportunity provided by high-throughput immunomics to improve this field.

Organs infected with Trypanosoma cruzi and DTU identification in the naturally infected rodent Octodon degus

Chagas disease is a public health problem in America. Its parasite, Trypanosoma cruzi, presents different discrete typing units (DTUs), colonizes organs of mammalian hosts in chronic infections, and presents tropism for particular organs in experimental infections. We evaluated T. cruzi tropism towards organs on the naturally infected rodent Octodon degus, identifying the parasites' DTUs, by means of conventional PCR and hybridization. Almost all the analyzed organs presented T. cruzi. More than 42% of the tested oesophagus, skin, skeletal muscle, brain and intestine showed T. cruzi DNA. Other nine types of organs were infected in over 15%. These results suggest that there is some tropism by T. cruzi in chronically infected O. degus. DTU TcV was present in 92.5% of infected organs with identified DTUs; this DTU is frequently reported in human infections in the Southern Cone of South America. Few organs showed mixed DTU infections. This is one of the few reports on the outcome of chronic natural T. cruzi-infection in wild mammal hosts exposed to naturally infected vectors.

Potential association of Trypanosoma cruzi DTUs TcV and TcVI with the digestive form of Chagas disease

The relationship among genetic diversity of Trypanosoma cruzi and clinical forms of Chagas disease remain elusive. In order to assess the possible association between different T. cruzi Discrete Typing Units (DTUs) and the clinical pictures of the disease, 205 chronic patients from Salta province, Argentina, were analysed. One hundred and twenty-two of these patients were clinically categorized as: cardiac 38.5% (47/122), digestive 15% (18/122), cardio-digestive 16% (20/122) and asymptomatic 30% (37/122). From each patient, blood samples were taken for both, Polymerase Chain Reaction (PCR) targeting kDNA and blood culture analyses. The presence of T. cruzi kDNA was detected in 43% (88/205) of the patients. T. cruzi DTUs were identified in 74% (65/88) of the kDNA positive patients by PCR-hybridization using specific probes. We detected the presence of DTUs TcI, TcII, TcV and TcVI. Single infections (i.e. presence of only one DTU in the sample) were detected in 38.64% of the samples (34/88), while mixed infections were 35.23% (31/88). TcV was the most prevalent DTU (60.3%- 53/88). The association analyses showed, for the first time to the best of our knowledge, that TcV and TcVI were associated with the digestive form of Chagas Disease (Fisher p = .0001).

Geographic distribution of Trypanosoma cruzi genotypes detected in chronic infected people from Argentina. Association with climatic variables and clinical manifestations of Chagas disease

Chronic Chagas disease affects large number of people in Latin America where it remains one of the biggest public health problems. Trypanosoma cruzi is genetically divided into seven discrete typing units (DTUs), TcI-TcVI and Tcbat, and exhibits differential distribution across vectors, host and transmission cycles. Clinical manifestations (cardiac, digestive and / or neurological) vary according to the geographical region; and the DTUs more frequently found in any of the chronic form of the disease, indeterminate or clinical, are TcI, TcII, TcV and TcVI. However, why they have a particular geographical distribution and how they affect the development of Chagas disease is still unknown. In this study, we assessed the geographic distribution of T. cruzi genotypes detected in chronic infected people from 57 localities of endemic regions of Argentina and analyzed their association with climatic variables. The prevalent DTUs detected in the whole population were TcV (47.4%) and TcVI (66.0%). TcI and TcII were identified in 5.2% each. All DTUs were detected in single and mixed infections (78.4% and 21.6%, respectively). TcV was found in infected people from localities with significantly higher average annual temperature, seasonal temperature and annual temperature range than those infected with TcVI. When we evaluated the association of DTUs with clinical manifestations of Chagas disease, the probability of finding TcVI in subjects with chronic Chagas cardiomyopathy (CCC) was higher than other DTUs, but without reaching statistical significance. Moreover, the probability of finding TcV in those who have not developed the disease after 20 years of infection was significantly higher than in CCC, either if it was present as unique DTU (reciprocal OR=4.95 95%CI: 1.42 to 17.27) (p=0.0117) or if it was also part of mixed infections (reciprocal OR=3.375; 95%CI: 1.227 to 9.276) (p=0.0264). There was no difference in the distribution of TcI between asymptomatic people and those with clinical manifestations, while TcII appeared more frequently in CCC cases, but without statiscal significance.

Human infectiousness and parasite load in chronic patients seropositive for Trypanosoma cruzi in a rural area of the Argentine Chaco

A key parameter in the transmission of vector-borne infections, including Chagas disease, is the ability of the different host species to transmit the parasite to the vector (infectiousness). Here, we determined infectiousness to the vector of Trypanosoma cruzi-seropositive humans examined by artificial xenodiagnosis (XD), established its relationship with T. cruzi DNA levels (a surrogate of intensity of parasitemia) quantified by real-time PCR (qPCR), and assessed whether infectiousness was associated with the body mass index (BMI), age, ethnic background and parasite genotype. XD was performed to 117 T. cruzi-seropositive residents from Pampa del Indio and parasite load was quantified in 81 of them. Using optical microscopy (OM) 33.6% of the seropositive people tested were infectious and this fraction nearly doubled (66.0%) when XD triatomines were examined by kDNA-PCR. The mean infectiousness (defined as the percentage of all infected triatomines detected by OM at any time point among the total number of insects examined by OM 30 days post-feeding) was 5.2%, and the mean parasite load was 0.51 parasite equivalents per ml. Infectiousness to the vector was associated negatively with age and BMI, and positively with the detection of parasitemia by kDNA-PCR, and parasite load by qPCR in bivariate analysis. Patients with a positive XD by OM exhibited a significantly higher mean parasite load. Using multiple regression, infectiousness was associated with parasite load (positively) and with the household presence of T. infestans and Qom ethnic group (negatively); no significant association was observed with age or its interaction with ethnicity. We did not find significant associations between identified DTUs and infectiousness or parasite load. Infectiousness was aggregated: 18% of the people examined by XD generated 80% of the infected triatomines. Detecting and treating the super-infectious fraction of the infected human would disproportionally impact on domestic transmission risks. Nonetheless, treatment of all eligible infected people who meet the inclusion criteria regardless of their parasitemia should be ensured to improve their prognosis.

Lineage-specific rapid diagnostic tests can resolve Trypanosoma cruzi TcII/V/VI ecological and epidemiological associations in the Argentine Chaco

BACKGROUND

Trypanosoma cruzi, the protozoan agent of Chagas disease, is comprised of at least 6 genetic lineages (TcI-TcVI). Their geographical distribution, clinical associations and reservoir hosts are not fully elucidated, as genotyping is hampered due to the difficulty in isolating representative populations of organisms. Lineage-specific serological techniques may address these issues.

METHODS

Trypanosoma cruzi lineage-specific serological assays were performed on human, canine, feline and armadillo sera from the Gran Chaco in northern Argentina, a region of ongoing transmission. Synthetic peptides representing lineage-specific epitopes of the trypomastigote small surface antigen (TSSA) were used in ELISA, and the TcII/V/VI shared epitope peptide (TSSApep-II/V/VI) was used in the Chagas Sero K-SeT rapid diagnostic test (RDT).

RESULTS

Chagas Sero K-SeT RDT, using Protein G to detect human and canine IgG, was at least as sensitive as TSSApep-II/V/VI ELISA using specific secondary antibodies. For sera from humans TSSApep-II/V/VI seroprevalence by Chagas Sero K-SeT was 273/393 (69.5%), for dogs 48/73 (65.8%) and for armadillos 1/7 (14.3%); by ELISA for cats 5/19 (26.3%). The seroprevalence for humans was similar to that for Bolivian patients, amongst whom we previously observed an association of TSSApep-II/V/VI seropositivity with severity of cardiomyopathy. In humans, prevalence of TSSApep-II/V/VI recognition was associated with locality, and with increasing and decreasing age within the Qom and Creole populations, respectively. For dogs TSSApep-II/V/VI recognition was associated with being born before community-wide insecticide spraying (P = 0.05) and with Qom household (P < 0.001).

CONCLUSIONS

We show here that Chagas Sero K-SeT RDT can replace ELISA for TSSApep-II/V/VI serology of humans and dogs; for humans there were statistically significant associations between a positive Chagas Sero K-SeT RDT and being resident in Area IV, and for dogs association with Qom household or with being born before the mass spraying campaign; we also show that with cats the TcII/V/VI epitope can be detected by ELISA. We assessed the lineage distribution in an unprecedented 83% of the human T. cruzi-seropositive population. These results form the basis for more detailed studies, enabling rapid in-the-field surveillance of the distribution and clustering of these lineages among humans and mammalian reservoirs of T. cruzi infection.