The South American Dry Diagonal, also called the Diagonal of Open Formations, is a large region of seasonally dry vegetation extending from northeastern Brazil to northern Argentina, comprising the Caatinga, Cerrado, and Chaco subregions. A growing body of phylogeography literature has determined that a complex history of climatic changes coupled with more ancient geological events has produced a diverse and endemic-rich Dry Diagonal biota. However, the exact drivers are still under investigation, and their relative strengths and effects are controversial. Pleistocene climatic fluctuations structured lineages via vegetation shifts, refugium formation, and corridors between the Amazon and Atlantic forests. In some taxa, older geological events, such as the reconfiguration of the São Francisco River, uplift of the Central Brazilian Plateau, or the Miocene inundation of the Chaco by marine incursions, were more important. Here, we review the Dry Diagonal phylogeography literature, discussing each hypothesized driver of diversification and assessing degree of support. Few studies statistically test these hypotheses, with most support drawn from associating encountered phylogeographic patterns such as population structure with the timing of ancient geoclimatic events. Across statistical studies, most hypotheses are well supported, with the exception of the Pleistocene Arc Hypothesis. However, taxonomic and regional biases persist, such as a proportional overabundance of herpetofauna studies, and the under-representation of Chaco studies. Overall, both Pleistocene climate change and Neogene geological events shaped the evolution of the Dry Diagonal biota, though the precise effects are regionally and taxonomically varied. We encourage further use of model-based analyses to test evolutionary scenarios, as well as interdisciplinary collaborations to progress the field beyond its current focus on the traditional set of geoclimatic hypotheses.
A Diagonal de Formações Abertas da América do Sul, também chamada de Diagonal Seca é uma grande região de vegetação sazonalmente seca que se estende do Nordeste do Brasil até o Norte da Argentina, composta pelas subregiões Caatinga, Cerrado e Chaco. Uma crescente literatura em filogeografia tem demonstrado que a diversa e endêmica biota Diagonal de Formações Abertas é produto de uma história complexa de mudanças climáticas, em conjunto com eventos geológicos mais antigos. Entretanto, os fatores específicos que geram essa diversidade e endemismo continuam sendo investigados, e há controvérsias em relação à importância relativa de cada um deles. Flutuações climáticas durante o Pleistoceno estruturaram linhagens através de mudanças na vegetação, formação de refúgios, e corredores entre a Floresta Amazônica e Mata Atlântica. Para alguns grupos taxonômicos, eventos geológicos durante o Neogeno, tal como a mudança no curso do São Francisco, o soerguimento do Planalto Central no Brasil, ou eventos durante o Mioceneo como a inundação do Chaco devido a incursões marinhas, foram mais importantes. No presente trabalho, nós revisamos a literatura sobre filogeografia na Diagonal de Formações Abertas, levantamos as hipóteses de diversificação sugeridas, e avaliamos seu grau de suporte. Poucos estudos testaram hipóteses estatisticamente, com maior parte do suporte atribuído aos padrões filogeográficos encontrados. Dentre os estudos que usaram uma abordagem estatística, a maioria das hipóteses são bem suportadas, exceto a hipótese dos arcos Pleistocênicos. Entretanto, vieses taxonômicos e regionais persistem, tal como a relativa prevalência de estudos herpetológicos e a falta de estudos sobre o Chaco. De forma geral, tanto as mudanças climáticas no Pleistoceno, quanto mudanças geológicas no Neogeno moldaram a evolução da Diagonal de Formações Abertas, apesar do efeito exato de cada um desses fatores variar dependendo da região e grupo taxonômico. Nós recomendamos o uso de análises baseadas em teste de modelos para testar cenários evolutivos, assim como colaborações interdisciplinares incluindo biólogos, geólogos e climatólogos para expandir o campo de estudo para além do seu atual foco atrelado às tradicionais hipóteses geoclimáticas mencionadas acima.

Chagas disease is more prevalent in socially vulnerable communities in the Gran Chaco Eco-region. The study evaluated the seroprevalence of Chagas disease and associated factors between May 2014 and September 2015, in indigenous communities of Santa Fe, Argentina, in the southern Chaco. Lysate ELISA and indirect hemagglutination tests were used to detect antibodies against Trypanosoma cruzi, and recombinant ELISA was used in the case of disagreement. Household surveys were conducted with the head of household about risk factors for the disease. Serological tests were conducted on 298 people from three indigenous communities, 127 male and 171 female. Seroprevalence was 18.5%. A total of 64 surveys were conducted; 82.8% of the heads of household were male, with a median age of 39 years, and 61.0% had not completed primary school. In 35.9% of the households, there was at least one member of the cohabiting group infected with T. cruzi. The level of education of the head of household showed a statistically significant association with Chagas disease (OR = 3.43), among all the risk factors studied. The prevalence of infection is lower than that of other indigenous communities of the Gran Chaco, probably because environmental conditions are moderating and disfavoring the establishment of the insect vector in homes, but also because of socioeconomic differences with the rest of the eco-region. Beyond this, serological controls are needed to prevent vertical transmission.

In the Gran Chaco region, the Pan American Health Organization (PAHO) declared the interruption of vector transmission of Chagas Disease in Paraguay and some district of Argentina.After a bibliographic search, by using the words \"Chagas, prevalence, children, Chaco\", on scientiphic articles indexed in Pubmed and Lilacs during the 2010-2021 period, we found nine studies which dealt with entomological data seroprevalence surveys of Chagas Disease in Argentine children and three studies in Bolivian children.More field studies need to be published to better understand the epidemiological situation in children from the region. Due to its social and ecological characteristics, the Gran Chaco region remains a hotspot for Chagas Disease affecting disproportionally rural communities and certain vulnerable ethnics groups.

BACKGROUND: Chronic Chagas cardiomyopathy (CChC) is the most common cause of death related to Chagas disease (CD). The aim of this study was to assess the feasibility of a combined rapid diagnostic test (RDT) and electrocardiographic (ECG) screening in a remote rural village of the Bolivian Chaco, with a high prevalence of CChC.
METHODS: Consecutive healthy volunteers > 15 years were enrolled in the community of Palmarito (municipality of Gutierrez, Santa Cruz Department, Bolivia) in February 2019. All patients performed an RDT with Chagas Stat-Pak® (CSP, Chembio Diagnostic System, Medford, NY, USA) and an ECG by D-Heart® technology, a low-cost, user-friendly smartphone-based 8-lead Bluetooth ECG. RDTs were read locally while ECGs were sent to a cardiology clinic which transmitted reports within 24 h from recording.
RESULTS: Among 140 people (54 men, median age 38(interquartile range 23-54) years), 98 (70%) were positive for Trypanosoma cruzi infection, with a linear, age-dependent, increasing trend (p < 0.001). Twenty-five (18%) individuals showed ECG abnormalities compatible with CD. Prevalence of ECG abnormalities was higher in infected individuals and was associated with higher systolic blood pressure and smoking. Following screening, 22 (16%) individuals underwent clinical evaluation and chest X-ray and two were referred for further evaluation. At multivariate analysis, positive CSP results (OR = 4.75, 95%CI 1.08-20.96, p = 0.039) and smoking (OR = 4.20, 95%CI 1.18-14.92, p = 0.027) were independent predictors of ECG abnormalities. Overall cost for screening implementation was <10 $.
CONCLUSIONS: Combined mobile-Health and RDTs was a reliable and effective low-cost strategy to identify patients at high risk of disease needing cardiologic assessment suggesting potential future applications.

BACKGROUND: Indoor residual spraying (IRS) of insecticides is a key method to reduce vector transmission of Trypanosoma cruzi, causing Chagas disease in a large part of South America. However, the successes of IRS in the Gran Chaco region straddling Bolivia, Argentina, and Paraguay, have not equalled those in other Southern Cone countries.
OBJECTIVE: This study evaluated routine IRS practices and insecticide quality control in a typical endemic community in the Bolivian Chaco.
METHODS: Alpha-cypermethrin active ingredient (a.i.) captured onto filter papers fitted to sprayed wall surfaces, and in prepared spray tank solutions, were measured using an adapted Insecticide Quantification Kit (IQK™) validated against HPLC quantification methods. The data were analysed by mixed-effects negative binomial regression models to examine the delivered insecticide a.i. concentrations on filter papers in relation to the sprayed wall heights, spray coverage rates (surface area / spray time [m2/min]), and observed/expected spray rate ratios. Variations between health workers and householders\' compliance to empty houses for IRS delivery were also evaluated. Sedimentation rates of alpha-cypermethrin a.i. post-mixing of prepared spray tanks were quantified in the laboratory.
RESULTS: Substantial variations were observed in the alpha-cypermethrin a.i. concentrations delivered; only 10.4% (50/480) of filter papers and 8.8% (5/57) of houses received the target concentration of 50 mg ± 20% a.i./m2. The delivered concentrations were not related to those in the matched spray tank solutions. The sedimentation of alpha-cypermethrin a.i. in the surface solution of prepared spray tanks was rapid post-mixing, resulting in a linear 3.3% loss of a.i. content per minute and 49% loss after 15 min. Only 7.5% (6/80) of houses were sprayed at the WHO recommended rate of 19 m2/min (± 10%), whereas 77.5% (62/80) were sprayed at a lower than expected rate. The median a.i. concentration delivered to houses was not significantly associated with the observed spray coverage rate. Householder compliance did not significantly influence either the spray coverage rates or the median alpha-cypermethrin a.i. concentrations delivered to houses.
CONCLUSIONS: Suboptimal delivery of IRS is partially attributable to the insecticide physical characteristics and the need for revision of insecticide delivery methods, which includes training of IRS teams and community education to encourage compliance. The IQK™ is a necessary field-friendly tool to improve IRS quality and to facilitate health worker training and decision-making by Chagas disease vector control managers.

Failure to control domestic Triatoma infestans in the Chaco is attributed to vulnerable adobe construction, which provides vector refuges and diminishes insecticide contact. We conducted a pilot to test the impact of housing improvement plus indoor residual spraying (IRS) on house infestation and vector abundance in a rural community in the Bolivian Chaco.
The intervention included three arms: housing improvement + IRS [HI], assisted IRS [AS] in which the team helped to clear the house pre-IRS and routine IRS [RS]. HI used locally available materials, traditional construction techniques and community participation. Vector parameters were assessed by Timed Manual Capture for 2 person-hours per house at baseline and medians of 114, 173, 314, 389 and 445 days post-IRS-1. A second IRS round was applied at a median of 314 days post-IRS-1.
Post-intervention infestation indices and abundance fell in all three arms. The mean odds of infestation was 0.29 (95% CL 0.124, 0.684) in the HI relative to the RS arm. No difference was observed between AS and RS. Vector abundance was reduced by a mean 44% (24.8, 58.0) in HI compared to RS, with no difference between AS and RS. Median delivered insecticide concentrations per house were lower than the target of 50 mg/m2 in >90% of houses in all arms.
Housing improvement using local materials and community participation is a promising strategy to improve IRS effectiveness in the Bolivian Chaco. A larger trial is needed to quantify the impact on reinfestation over time.

The chloroplast genome of Tabebuia nodosa is described and characterized here. This species is endemic to the Chaco and the first species of Tabebuia to have its organelle genome sequenced, providing a genomic resource for phylogenetic inferences. The plastome of T. nodosa is 158,454 bp in length, with a large single-copy of 85,406 bp, a small single-copy of 12,785 bp, and inverted repeats of 30,116 bp each. It contains 131 genes, with 86 protein-coding genes, 37 tRNA, and 8 rRNA. Overall, the GC content is 38.2%. The T. nodosa plastome resembles the structural organization of plastomes commonly found in flowering plants, including those of other genera of Bignoniaceae. A phylogenetic analysis combining a subset of Bignoniaceae plastomes confirms the placement of T. nodosa within the Tabebuia alliance with maximum support.

The morphological variations of four populations of geographically isolated Triatoma infestans located in the area of inter-Andean valleys and Chaco of Chuquisaca, Bolivia, were evaluated. Fifty-three females and sixty-one males were collected in the peri-domicile and analyzed with geometric morphometrics tools to study the patterns of the head and wing shape variation. The principal component analysis and canonical variate analysis revealed morphological variations between the populations studied, which were then confirmed by the permutation test of the differences between populations using Mahalanobis and Procustes distances. The multivariate regression analysis shows that the centroid size influences the shape of the heads and wings. T. infestans of the inter-Andean valleys are longer in the head and wings compared to the population of the Chaco. We propose that the geometric shape variation may be explained by geographical changes in climatic conditions, peri-domiciliar habitats, food source quality, and the use of insecticides.

Chagas disease (CD) remains a public health concern in several Latin American countries. At global level, Bolivia has the highest CD burden and the Chaco region, in the southeast of the country, is the most affected area. We report the results of four serosurveys for Trypanosoma cruzi antibodies, carried out approximately ten years apart from each other, during the lapse 1987-2013, in different localities of the Bolivian Chaco.
Four cross-sectional surveys were conducted in various localities, mostly rural, of the Bolivian Chaco, during the period 1987-2013.
Although a reliable analysis of CD epidemiological trend is challenging, a partial reduction of anti-T. cruzi seroprevalence over the past four decades in the Bolivian Chaco may be assumed. In particular, in 1987 the exposure to T. cruzi in rural setting was universal since the first years of life, while it resulted gradually lower and age-dependent thereafter. Moreover, T. cruzi seroprevalence among women of reproductive age (15-45 years) has been persistently high in rural areas.
T. cruzi transmission is still active and CD remains a concern throughout the Bolivian Chaco. More efforts are needed in order to achieve a sustainable interruption of vector-borne CD transmission in this area.

Trypanosoma cruzi, the etiological agent of Chagas disease, was initially classified into 6 Discrete Typing Units (DTUs). The hybrid DTUs TcV and TcVI are the most frequent in domestic transmission cycles throughout the Southern Cone countries of South America. Here, we genotyped parasite isolates from human residents in Pampa del Indio municipality, Chaco, to further characterize the structure of T. cruzi populations, and to assess the degree of overlapping between the domestic and sylvatic transmission cycles. Artificial xenodiagnostic tests were performed to blood samples from 125 T. cruzi-seropositive people (age range, 3-70 years) who represented 14.3% of all seropositive residents identified. Parasites were obtained from feces of T. cruzi-infected Triatoma infestans examined 30 or 60 days after blood-feeding, and grown in vitro. The cultured parasites were genotyped by means of two PCR-based protocols. DTUs were determined from 39 (31%) patients residing in 28 dwellings. The only DTUs identified were TcV (92%) and TcVI (8-36%). Households with more than one parasite isolate consistently displayed the same DTU. Further sequencing of a fragment of the TcMK gene from selected samples argue against the occurrence of mixed TcV-TcVI infections in the study population. Sequencing data revealed an unexpected degree of genetic variability within TcV including two apparently robust subgroups of isolates. Our results for human residents confirm the predominance of hybrid lineages (TcV and to a much lesser extent TcVI) and the absence of sylvatic genotypes (TcI and TcIII) in (peri)domestic transmission cycles in the Argentinean Chaco area. 245 words.