Gran Chaco Region Research Articles

Predominance of hybrid discrete typing units of Trypanosoma cruzi in domestic Triatoma infestans from the Bolivian Gran Chaco region

In the Gran Chaco region the reinfestation by Triatoma infestans remains a major problem for control of Chagas disease. Trypanosoma cruzi the agent of the illness presents a broad genetic intraspecific variability which is poorly documented in the Bolivian Gran Chaco. This work presents the identification of the discrete typing units (DTUs) currently recognized for T. cruzi in T. infestans populations collected before and after residual insecticide spraying in four villages in this region. Before spraying, of 84 samples, the frequencies of the DTUs identified by using the multiplex PCR based on the non transcribed spacer of the mini-exon gene (MMPCR) were 0.21 for TcI, 0.70 for TcII/TcV/TcVI, and 0.17 for TcIII/TcIV and no significant difference was observed after spraying (76 samples). Moreover 13% of the total sample corresponds to T. infestans specimens with mixed infection of DTUs of which three were TcII/TcV/TcVI with TcIII/TcIV. The partial sequences of T. cruzi Gpi gene obtained from 14 PCR products agree the MMPCR DTU identification and allowed to precise the occurrence of TcIII, TcII and hybrid TcV/TcVI stocks which were not discriminated by the MMPCR.Given the high prevalence of hybrid stocks, the authors ask whether the recombination event at the origin of hybrids would have taken place in the Gran Chaco where the putative parents are also present.

Spatial Heterogeneity and Risk Maps of Community Infestation by Triatoma infestans in Rural Northwestern Argentina

BackgroundFifty years of residual insecticide spraying to control Triatoma infestans in the Gran Chaco region of northern Argentina, Paraguay and Bolivia shows that vertically coordinated interventions aiming at full coverage have limited effects and are unsustainable. We quantified the spatial distribution of T. infestans domestic infestation at the district level, identified environmental factors associated with high infestation and then explored the usefulness of risk maps for the spatial stratification of interventions.Methods and FindingsWe performed spatial analyses of house infestation data collected by the National Chagas Service in Moreno Department, northern Argentina (1999–2002). Clusters of high domestic infestation occurred in the southwestern extreme of the district. A multi-model selection approach showed that domestic infestation clustered in areas of low elevation, with few farmlands, high density of rural houses, high mean maximum land surface temperature, large NDVI, and high percentage of degraded and deforested lands. The best model classified 98.4% of the communities in the training dataset (sensitivity, 93.3%; specificity, 95.4%). The risk map evidenced that the high-risk area only encompassed 16% of the district. By building a network-based transportation model we assessed the operational costs of spatially contiguous and spatially targeted interventions. Targeting clusters of high infestation would have reached ∼80% of all communities slated for full-coverage insecticide spraying, reducing in half the total time and economic cost incurred by a spatially contiguous strategy.Conclusions and SignificanceIn disperse rural areas where control programs can accomplish limited coverage, consideration of infestation hot spots can contribute to the design and execution of cost-effective interventions against Chagas disease vectors. If field validated, targeted vertical control in high risk areas and horizontal control in medium to low risk areas may provide both a logistically and economically feasible alternative to blanket vertical insecticide spraying when resources are limited.

Biological behavior of different Trypanosoma cruzi isolates circulating in an endemic area for Chagas disease in the Gran Chaco region of Argentina

The biological behavior of the different Trypanosoma cruzi strains is still unclear and the importance of exploring the relevance of these differences in natural isolates is of great significance. Herein we describe the biological behavior of four T. cruzi isolates circulating sympatrically in a restricted geographic area in Argentina endemic for Chagas Disease. These isolates were characterized as belonging to the Discrete Typing Units (DTUs) TcI, TcIII, TcV and TcVI as shown by Multilocus Enzyme Electrophoresis and Multilocus Sequence Typing. In order to study the natural behavior of the different isolates and to preserve their natural properties, we developed a vector transmission model that allows their maintenance in the laboratory. The model consisted of serial passages of these parasites between insect vectors and mice. Vector-derived parasite forms were then inoculated in C57BL/6J mice and number of parasite in peripheral blood, serological response and histological damage in acute and chronic phases of the infection were measured. Parasites from DTUs TcI, TcIII and TcVI were detected by direct fresh blood examination, while TcV parasites could only be detected by Polimerase Chain Reaction. No significant difference in the anti-T. cruzi antibody response was found during the chronic phase of infection, except for mice infected with TcV parasites where no antibodies could be detected. Histological sections showed that TcI isolate produced more damage in skeletal muscle while TcVI induced more inflammation in the heart. This work shows differential biological behavior among different parasite isolates obtained from the same cycle of transmission, permitting the opportunity to formulate future hypotheses of clinical and epidemiological importance.

Exploring the association between Trypanosoma cruzi infection in rural communities and environmental changes in the southern Gran Chaco

The association between land use and land cover changes between 1979-2004 in a 2.26-million-hectare area south of the Gran Chaco region and Trypanosoma cruzi infection in rural communities was analysed. The extent of cultural land, open and closed forests and shrubland up to 3,000 m around rural communities in the north, northwest and west of the province of Córdoba was estimated using Landsat satellite imagery. The T. cruzi prevalence was estimated with a cross-sectional serological survey conducted in the rural communities. The land cover showed the same patterns in the 1979, 1999 and 2004 satellite imagery in both the northwest and west regions, with shrinking regions of cultured land and expanding closed forests away from the community. The closed forests and agricultural land coverage in the north region showed the same trend as in the northwest and west regions in 1979 but not in 1999 or 2004. In the latter two years, the coverage remote from the communities was either constant or changed in opposite ways from that of the northwest and west regions. The changes in closed forests and cultured vegetation alone did not have a significant, direct relationship with the occurrence of rural communities with at least one person infected by T. cruzi. This study suggests that the overall decrease in the prevalence of T. cruzi is a consequence of a combined effect of vector control activities and changes in land use and land cover.

Prevalence of Trypanosoma cruzi infection in pregnant Latin American women and congenital transmission rate in a non-endemic area: the experience of the Valencian Health Programme (Spain)

This study describes the results of the health programme implemented in the Valencian Community (Spain) to achieve an early diagnosis of Chagas disease in pregnant Latin American women and their newborns. During 2009 and 2010, 1975 women living in the health districts of three university hospitals were enrolled via midwives or at the time of delivery. Diagnosis of disease was performed using two serological tests with different antigens. Congenital infection was diagnosed by parasitological, molecular or serological methods from blood samples obtained at birth or in subsequent controls. The overall seroprevalence of Chagas infection in pregnant women from 16 different endemic countries was 11·4%. Infection was higher in those from countries in the Gran Chaco Region (Bolivia, 34·1%; Paraguay, 7·4%; Argentina, 5·3%). Eight newborn infants from Bolivian mothers had congenital Chagas which represents a vertical transmission rate of 3·7%. In conclusion, this work supports the benefits of offering an early diagnosis to pregnant women and newborns during routine prenatal healthcare.

Hidden sylvatic foci of the main vector of Chagas disease Triatoma infestans: threats to the vector elimination campaign?

BackgroundEstablishing the sources of reinfestation after residual insecticide spraying is crucial for vector elimination programs. Triatoma infestans, traditionally considered to be limited to domestic or peridomestic (abbreviated as D/PD) habitats throughout most of its range, is the target of an elimination program that has achieved limited success in the Gran Chaco region in South America.Methodology/Principal FindingsDuring a two-year period we conducted semi-annual searches for triatomine bugs in every D/PD site and surrounding sylvatic habitats after full-coverage spraying of pyrethroid insecticides of all houses in a well-defined rural area in northwestern Argentina. We found six low-density sylvatic foci with 24 T. infestans in fallen or standing trees located 110–2,300 m from the nearest house or infested D/PD site detected after insecticide spraying, when house infestations were rare. Analysis of two mitochondrial gene fragments of 20 sylvatic specimens confirmed their species identity as T. infestans and showed that their composite haplotypes were the same as or closely related to D/PD haplotypes. Population studies with 10 polymorphic microsatellite loci and wing geometric morphometry consistently indicated the occurrence of unrestricted gene flow between local D/PD and sylvatic populations. Mitochondrial DNA and microsatellite sibship analyses in the most abundant sylvatic colony revealed descendents from five different females. Spatial analysis showed a significant association between two sylvatic foci and the nearest D/PD bug population found before insecticide spraying.ConclusionsOur study shows that, despite of its high degree of domesticity, T. infestans has sylvatic colonies with normal chromatic characters (not melanic morphs) highly connected to D/PD conspecifics in the Argentinean Chaco. Sylvatic habitats may provide a transient or permanent refuge after control interventions, and function as sources for D/PD reinfestation. The occurrence of sylvatic foci of T. infestans in the Gran Chaco may pose additional threats to ongoing vector elimination efforts.

MtDNA diversity in azara's owl monkeys (Aotus azarai azarai) of the Argentinean Chaco

Owl monkeys (Aotus spp.) inhabit much of South America yet represent an enigmatic evolutionary branch among primates. While morphological, cytogenetic, and immunological evidence suggest that owl monkey populations have undergone isolation and diversification since their emergence in the New World, problems with adjacent species ranges, and sample provenance have complicated efforts to characterize genetic variation within the genus. As a result, the phylogeographic history of owl monkey species and subspecies remains unclear, and the extent of genetic diversity at the population level is unknown. To explore these issues, we analyzed mitochondrial DNA (mt DNA) variation in a population of wild Azara's owl monkeys (Aotus azarai azarai) living in the Gran Chaco region of Argentina. We sequenced the complete mitochondrial genome from one individual (16,585 base pairs (bp)) and analyzed 1,099 bp of the hypervariable control region (CR) and 696 bp of the cytochrome oxidase II (COII) gene in 117 others. In addition, we sequenced the mitochondrial genome (16,472 bp) of one Nancy Ma's owl monkey (A. nancymaae). Based on the whole mtDNA and COII data, we observed an ancient phylogeographic discontinuity among Aotus species living north, south, and west of the Amazon River that began more than eight million years ago. Our population analyses identified three major CR lineages and detected a high level of haplotypic diversity within A. a. azarai. These data point to a recent expansion of Azara's owl monkeys into the Argentinean Chaco. Overall, we provide a detailed view of owl monkey mtDNA variation at genus, species, and population levels.

Ethnobiological Classification in Two Indigenous Languages of the Gran Chaco Region: Toba (Guaycuruan) and Maká (Mataco-Mataguayan)

This article examines the linguistic devices involved in the classification of nouns referring to the plant and animal world in two languages of the Gran Chaco area: Toba (Guaycuruan) and Maká (Mataco-Mataguayan). Drawing on previous studies of nominal classification in these languages, it analyzes how derivational morphology and nominal composition are used as mechanisms in categorizing the natural world in the formation of ethno-botanical and ethnozoological lexicon. The article contributes to the typology of nominal classification in general and in particular to that of the indigenous languages of the Gran Chaco region.

First report of colonies of sylvatic Triatoma infestans (Hemiptera: Reduviidae) in the Paraguayan Chaco, using a trained dog.

In the Gran Chaco region, control of Triatoma infestans has been limited by persistent domestic infestations despite the efforts of the Vector Control Services. In Paraguay, this region is the highest endemic area in the country, showing high levels of indoor and outdoor infestation. Although sylvatic T. infestans have been found in the Bolivian and Argentine Chaco, similar searches for sylvatic populations of this species in Paraguay had been unsuccessful over the last 20 years. Here we present a new approach to detecting sylvatic Triatominae, using a trained dog, which has successfully confirmed sylvatic populations of T. infestans and other triatomine species in Paraguay. A total of 22 specimens corresponding to dark morph forms of T. infestans were collected, and 14 were confirmed as T. infestans by the mitochondrial cytochrome B gene analysis. Through this analysis, one of which were previously reported and a second that was a new haplotype. Triatomines were captured from amongst vegetation such as dry branches and hollows trees of different species such Aspidosperma quebracho-blanco, Bulnesia sarmientoi and Stetsonia coryne. The colonies found have been small and without apparent infection with Trypanosoma cruzi. During the study, Triatoma sordida and Triatoma guasayana have also been found in ecotopes close to those of T. infestans.

Ships Stranded in the Forest

In this article, I examine the debris that modernist projects leave in space and the ways in which these vestiges are interpreted, generations later, by people haunted by the long-term reverberations of their ruination. Drawing on theories of negativity, I look at local memories woven around these spatial sedimentations with the aim of examining the interpenetration of space, history, decline, and subjectivity. My narrative focuses on the remains of steamships that the attempts to turn the Bermejo River into a commercial fluvial route left around the town of Rivadavia in the Gran Chaco region of northern Argentina. In the 1860s and 1870s, businessmen and officials hailed the navigation of Bermejo as a project that would bring progress and prosperity to a savage region under the control of indigenous groups. Shortly thereafter, the Bermejo shifted its course, the navigation schemes collapsed, and Rivadavia entered a period of decline from which it never fully recovered. In this article, I examine how local...

Natural pharmacopoeia used in traditional Toba medicine for the treatment of parasitosis and skin disorders (Central Chaco, Argentina)

To assess the knowledge and use of natural pharmacopoeia for the treatment of parasitosis and skin disorders, as well as for the control of their etiological agents or vectors, of a Toba community in Central Chaco, Argentina. Information was obtained by open, extensive and recurrent interviews and semi-structured surveys. Plant and animal pharmacopoeia was documented by collecting material in field assays carried out in the company of informers. The list of applications with the greatest consensus of uses, the list of species with most medicinal applications and the list of species with the highest reputation (according to the level of fidelity) for the aforementioned disorders were obtained using quantitative methods. A total of 178 medicinal uses were documented corresponding to 87 species (72 plant and 15 animal species) belonging to 51 different families (39 plant and 12 animal families). The most represented families according to the number of species were Solanaceae (7 species), Asteraceae (6 species) and Fabaceae (5 species) for plants, and Bovidae (3 species) for animals. Although the list of medicinal species includes some symbolical applications, others are supported by phytochemical information. In other cases the applications coincide with other pharmacopoeias of the Gran Chaco region indicating the presence of an active exchange of knowledge through interethnic contacts.

"Cumplí tu sueño": Pedagogía de la oniromancia y conocimiento práctico entre las mujeres pilagá - Gran Chaco (Formosa, Argentina)

The article reflects on the way dream experiences have been addressed by anthropology, taking up my fieldwork experience with Pilaga women of the Gran Chaco Region. It discusses the assumptions, implicit or explicit, of some anthropological approaches to the analysis of dreams and their excessive concentration on the relation of dreams to shamanism and mythology. Based on ethnographic material obtained with some Pilaga women, it takes up the links, as established by one of my main collaborators, between dreaming, narrating, interpreting, doing, and copying. It aims to emphasize that the relations between dream experience and practical action correspond to what I call the pedagogy of oneiromancy, a category that stresses the web that connects representations to the behavior and actions associated with the life trajectories and recent experiences of indigenous women.

Seroprevalence of Trypanosoma cruzi infection and vector control activities in rural communities of the southern Gran Chaco (Argentina)

We compared age-related seroprevalence of Trypanosoma cruzi infection with history of vector control interventions and social and ecological changes in three historically endemic departments of Cordoba province, Argentina, covering an area of 42,600 km(2) of the Gran Chaco region. Using a cross sectional design, blood samples of 5240 people between 6 months and 40 years of age, living in 192 rural communities were analyzed to detect T. cruzi infection using ELISA tests, and confirmed with indirect immunofluorescent antibody test and indirect haemoagglutination. Overall seroprevalence was 5.4%, 7.9% and 7.5% in the north, northwest and west studied areas (average for all areas 6.95%). Seroprevalence for T cruzi increased with population age, especially in age classes older than 15 years of age. Communities of the north and west areas showed 0.59% seroprevalence for T. cruzi in children below 15 years of age, whereas children of the same age in the northwest region showed a seroprevalence of 3.08%. Comparative analyses indicate that vector control activities and land use changes during the last decades are the most likely causes of the overall reduction of T. cruzi prevalence. Results suggest that the vectorial transmission of T. cruzi has been strongly reduced and probably interrupted in the north and west areas, but it is still active in the northwestern rural settlements of Córdoba province.

DETERMINANTS AND PREDICTION OF BROAD-SCALE PLANT RICHNESS ACROSS THE WESTERN NEOTROPICS1

Patterns of broad-scale plant species richness are thought to be largely determined by (1) variation in energy and water availability among sampling units (species energy hypothesis), (2) habitat and topographic heterogeneity within sampling units (spatial heterogeneity hypothesis), and (3) regional differences in geographic configuration and history (regional effects hypothesis). However, lack of taxonomic and distribution data, particularly for tropical regions, has impeded assessments of the relative importance of these three hypotheses. We used a large botanical database to estimate the pattern of relative vascular plant richness across the western Neotropics and regression models to measure the extent to which this estimated pattern supported predictions from each of the above three hypotheses. Variation in plant richness across three major paleophysiographic regions (northwest South America, southern Central America, and northern Central America) was primarily predicted by the spatial heterogeneity hypothesis, with secondary contributions from the species energy hypothesis and, to a lesser extent, the regional effects hypothesis. Regression models that incorporated the relative contributions of all three hypotheses predicted peaks of relative species richness mostly in topographically complex areas (e.g., Sierra Madre de Chiapas, Cordillera de Tilarán, Cordillera de Talamanca, Panama's Cordillera Central, the Andes, and the Venezuelan Guayana); relatively low richness in central Mexico and Yucatán, Los Llanos of Venezuela, and in the Gran Chaco region of Bolivia, Paraguay, and Argentina; and a richness trough in lowland Amazonia relative to southern Central America, the Andes, and the Venezuelan Guayana. We discussed the contrast between our results and previous assessments that found plant richness to be primarily determined by the species energy hypothesis and predicted different patterns of plant richness across the western Neotropics.

Mitochondrial DNA control region sequence analysis of Mataco–Guaicurú speaking tribes from Argentina

In this work we analyze three Mataco–Guaicurú speaking Amerindian tribes that inhabit the Northern Argentinean portion of Gran Chaco region. One hundred and sixty-eight samples of unrelated males belonging to two linguistic families: Guaycurú (Toba from Chaco, n = 27; Toba from Formosa, n = 37 and Pilaga from Formosa, n = 56) and Mataco (Wichi from Formosa, n = 48) were investigated. The entire Control Region of the mtDNA from position 16024 to 576 was sequenced. EMPOP sequencing strategy was employed including the use of 10 primers for each sample. Specific haplotypes were found in these populations with very high frequency. These findings could provide clues to address the ethnicity of a sample in routine forensic casework.

Experimental evaluation of insecticidal paints against Triatoma infestans (Hemiptera: Reduviidae), under natural climatic conditions

BackgroundTriatoma infestans is the main vector of Chagas disease in the Gran Chaco region of South America. The traditional spraying technique used for the application of pyrethroid insecticides has shown low efficiency in the elimination of the vector species populations occupying peridomestic structures of rural houses in the endemic area of Argentina. As part of studies looking for better alternatives, we evaluated the residual effect of insecticidal paints on the mortality of fourth instar nymphs of T. infestans.ResultsThe study was based on an experimental design that included two groups treated with an organophosphate (Inesfly 5A IGR™) and a pyrethroid (Inesfly 5A IGR NG™) formulations of the paint, that were applied on wood, cement blocks and adobe bricks under natural climatic conditions. A third group was an untreated control. Both paint formulations showed very long residual activity, producing mortality of 84% and 98% (pyrethroid and organophosphate formulations, respectively) after 12 months of the paint application. After eight months, nymphs exposed during 6 hours to the painted surfaces with the pyrethroid and organophosphate formulations showed 81.33% and 100% mortality, respectively.ConclusionThe organophosphate- and pyrethroid-based insecticidal paints showed a very long residual activity on the mortality of fourth instar nymphs of T infestans, compared with the traditional spraying technique used for the application of pyrethroid insecticides in peridomestic structures of rural houses in the endemic region for Chagas disease in the Gran Chaco of Argentina. The application of the paints by trained personnel of the vector control programmes could be considered as an alternative control tool in areas where the traditional methods have failed or showed low efficacy.

Sustainability of vector control strategies in the Gran Chaco Region: current challenges and possible approaches.

Sustainability has become a focal point of the international agenda. At the heart of its range of distribution in the Gran Chaco Region, the elimination of Triatoma infestans has failed, even in areas subject to intensive professional vector control efforts. Chagas disease control programs traditionally have been composed of two divorced entities: a vector control program in charge of routine field operations (bug detection and insecticide spraying) and a disease control program in charge of screening blood donors, diagnosis, etiologic treatment and providing medical care to chronic patients. The challenge of sustainable suppression of bug infestation and Trypanosoma cruzi transmission can be met through integrated disease management, in which vector control is combined with active case detection and treatment to increase impact, cost-effectiveness and public acceptance in resource-limited settings. Multi-stakeholder involvement may add sustainability and resilience to the surveillance system. Chagas vector control and disease management must remain a regional effort within the frame of sustainable development rather than being viewed exclusively as a matter of health pertinent to the health sector. Sustained and continuous coordination between governments, agencies, control programs, academia and the affected communities is critical.

Response of Triatoma infestans to pour-on cypermethrin applied to chickens under laboratory conditions

This article reports the effects of a pour-on formulation of cypermethrin (6% active ingredient) applied to chickens exposed to Triatoma infestans, the main vector of Chagas disease in rural houses of the Gran Chaco Region of South America. This study was designed as a completely random experiment with three experimental groups and five replicates. Third instar nymphs were fed on chickens treated with 0, 1 and 2 cc of the formulation. Nymphs were allowed to feed on the chickens at different time intervals after the insecticide application. Third-instar nymphs fed on treated chickens showed a higher mortality, took less blood during feeding and had a lower moulting rate. The mortality rate was highest seven days after the insecticide solution application and blood intake was affected until 30 days after the application of the solution.

Spatial Stratification of House Infestation by Triatoma infestans in La Rioja, Argentina

Vectorial transmission of Chagas disease has been decreasing over the past few decades because of effective vector control programs in the southern cone of South America. However, the disease is still actively transmitted within the Gran Chaco region. In this area, vector populations are abundant and highly prevalent in poor rural houses. This study analyses the spatial pattern of rural house infestation by Triatoma infestans in a 56,000 km(2) area in the province of La Rioja, Argentina, before the re-initiation of systematic activity on vector control intervention. Data on 5,045 rural houses show that infestation has high spatial heterogeneity, with highly infested localities concentrated in a few areas. House infestation has a negative significant relationship with locality size. Rural houses in the region are highly dispersed and this feature has been and will remain a challenge for any vigilance system to be installed in the region.

Landscape changes influence the reproductive behaviour of a key ‘capital breeder’ snake ( Boa constrictor occidentalis) in the Gran Chaco region, Argentina

Many wild reptile species are threatened by habitat loss. However, the way in which changes in landscape patterns influence intraspecific ecological processes is not completely understood. Boa constrictor occidentalis is an endangered species and has a special conservation value since it is endemic of dry forests in the Gran Chaco region. Because the Gran Chaco is largely threatened due to habitat loss it is necessary to know how landscape changes influence this species. Therefore, we evaluated the effects of forest loss and landscape composition on the reproductive life-history parameters. Landscape changes were assessed by analyzing satellite imagery and reproductive parameters were determined by ultrasound images of the reproductive structures. The obtained results indicate that habitat loss may affect body condition, clutch size and testicular volume of the Argentine boa constrictor. We also found that the spatial pattern of vegetation influences the distribution of females and males in the landscape. Matting aggregations are scarce in shrublands. Therefore, our study shows that forest loss could enhance vulnerability to extirpation through constraints placed on reproduction. We encourage resource managers to evaluate sensitive reproductive life-history parameters as well as habitat deterioration to asses the conservation status of the populations of the Argentine boa constrictor. Since the Gran Chaco forest, a key habitat to the species’ reproduction, is largely threatened, strong conservation action is needed to halt and reverse forest loss in this region.