Chagas prevention and control in an endemic area from the Argentinian Gran Chaco Region: Data from 14 years of uninterrupted intervention.

BACKGROUND: Chagas Disease (ChD) is a Neglected Tropical Disease (NTD) affecting 6 to 7 million people worldwide, mostly from Latin America. In Argentina, a national control program has been implemented since 1962, yet there are still an estimated 1.6 million infected individuals. Control programs were based almost exclusively on entomological surveillance and chemical control of households and were not continuous given a lack of coordination and resources. Argentina´s ChD program was originally vertical and centralized; later, it was partially and, in general, unsuccessfully transferred to the provinces. Herein, we describe the implementation of a control program for ChD with an ecohealth approach in rural settlements around the city of Añatuya, Santiago del Estero. METHODS: The program included yearly household visits for entomological surveillance and control, health promotion workshops, and structural house improvements. Improved structures included internal and external walls and roofs, as well as the construction of water wells and latrines, and the organization and improvement of peri-domestic structures. Activities were carried out by specifically trained personnel except for house improvements, which were performed by the community, under technical guidance and provision of materials. Data was collected using standardized questionnaires for household characterization, entomological infestation status and chemical control activities. RESULTS: This program was continuously implemented since 2005 with high community participation and adherence, incorporating 13 settlements and 502 households. During the surveillance phase, 4,193 domiciliary inspections were performed, and both the intra- and peri-domestic infestation rate were reduced from 17.9% to 0.2% (P < 0.01) and from 20.4% to 3%, respectively. Additionally, 399 households were structurally improved. CONCLUSION: The program is still ongoing and, after 14 years of implementation, has built social networks and collaboration between implementers and beneficiaries with a reduction of T. infestans infestation in the intra- and peri-domicile. This reduction, especially inside the household, has enabled access to diagnosis and treatment of the population, with minimal risk of re-infection.

A multidisciplinary, collaborative, inter-agency and comprehensive approach for the control of Chagas Disease as a public health problem in Guatemala.

The Pan American Health Organization (PAHO) has defined Chagas Disease hotspots in Central America associated with the vector Triatoma spp. Triatoma dimidiata is a native vector adapted to multiple environments, including intra-domestic and peri-domestic habitats. A multi-institutional project named "Alliances for the elimination of Chagas in Central America" was created to help reduce the incidence of the disease in the region. Activities performed in the field as part of the project included aspects of vector surveillance and control, improvement of houses, diagnosis and treatment of individuals, health promotion, training of human resources and identification of access barriers to diagnosis and treatment. As a base line study, eleven villages, comprised of 1,572 households, were entomologically evaluated (83.4% overall participation); five were found to have very high infestation rates (>20%), three had high infestation rates (8-20%) and three had low-infestation rates (<8%), coinciding with the category of infestation-risk of the houses within each village. Serological tests were carried out in 812 people (>80% participation) in two of the 11 villages and none of the 128 children tested, less than 5 years of age, were positive for Trypanosoma cruzi infection. Community participation in all the activities was high (>70%). The collaboration between several subnational, national, and international institutions, each with specific roles, promoted community participation in the activities of vector control and patient care, thus, establishing a baseline to continue implementing and monitoring project progress.

Reply: Geospatial tools and Chagas control: A critical comment on the paper published under Weinberg et al., Evaluation and planning of Chagas control activities using geospatial tools. Geospat Health 14:229-238.

We present here a reply on the observations and comments of Dr. David Gorla regarding our article "Evaluation and planning of Chagas control activities using geospatial tools" published in Geospatial Health 2019;14:229-238. (doi: 10.4081/gh.2019.786).

Seroprevalence of the Strongyloides stercoralis Infection in Humans from Yungas Rainforest and Gran Chaco Region from Argentina and Bolivia.

The threadworm, Strongyloides stercoralis, is endemic in tropical and subtropical areas. Data on the prevalence and distribution of infection with this parasite species is scarce in many critical regions. We conducted a seroprevalence study of S. stercoralis infection in 13 locations in the Gran Chaco and Yungas regions of Argentina and Bolivia during the period 2010-2016. A total of 2803 human serum samples were analyzed by ELISA-NIE which has a sensitivity of 75% and specificity of 95%. Results showed that 551 (19.6%) of those samples were positive. The adjusted prevalence was 20.9%, (95% confidence interval (CI) 19.4%-22.4%). The distribution of cases was similar between females and males with an increase of prevalence with age. The prevalence in the different locations ranged from 7.75% in Pampa del Indio to 44.55% in Santa Victoria Este in the triple border between Argentina, Bolivia, and Paraguay in the Chaco region. Our results show that S. stercoralis is highly prevalent in the Chaco and Yungas regions, which should prompt prospective surveys to confirm our findings and the design and deployment of control measures.

Resistance to deltamethrin in Triatoma infestans: microgeographical distribution, validation of a rapid detection bioassay and evaluation of a fumigant canister as control alternative strategy.

Triatoma infestans (Klug) (Hemiptera: Reduviidae) is the main vector of Chagas disease in the Southern Cone of America and resistance to pyrethroid insecticides has been detected in several areas from its geographical distribution. Pyrethroid resistance presents a complex geographical pattern at different spatial scales. However, it is still unknown if the toxicological variability is a common feature within villages of the Gran Chaco were high resistance was descripted. The objectives of this study were to determine: (a) the microgeographical distribution of the deltamethrin-resistance in insects from Pampa Argentina village, (b) the performance of the insecticide impregnated paper bioassay to evaluate deltamethrin-resistance in field collected insects and (c) the lethal activity of the fumigant canister containing DDVP against insects resistant to deltamethrin. High survival of T. infestans exposed to discriminant dose was observed in the samples of all the evaluated dwellings, suggesting that the resistance to deltamethrin is homogeneous at the microgeographical level. Resistance determination by impregnated paper bioassay was similar to traditional topical determination, highlighting the use of this rapid methodology in field large-scale monitoring. The fumigant canister was not effective against resistant insects, remarking the need to develop suitable formulations that ensure minimal toxicological risk and high effectivity.

Evaluation and planning of Chagas control activities using geospatial tools.

Chagas continues to be a relevant public health problem in Latin America. In this work, we present a spatiotemporal analysis applied for the evaluation and planning of Chagas vector control strategies. We analysed the spatial distribution of the vector Triatoma infestans infestation related to ongoing control interventions cycles in rural communities near Añatuya, Santiago del Estero, Argentina. A geographical information system was developed for the spatial analysis obtaining, for each house, variables that describe the history of spraying and infestation at each time of interventions. Bi-dimensional histograms were used to describe the spatiotemporal pattern of these activities and peri-domestic infestation at the last intervention was modelled by a neural network model. We qualitatively evaluate control programmes considering the history of infestation and spraying from a spatiotemporal point of view, incorporating new ways of visualising this information. Predictions are based on novel, non-linear models and spatiotemporal indices, which should be useful for strategically allocating Chagas control resources in the future and thus help to better plan spraying strategies.

Spatial analyzes of triatomine infestation indices and their association to the actions of a Chagas disease program and environmental variables during a 5-year intervention period.

Vector control of Chagas disease in the past decades has been mainly based on chemical control. Fundación Mundo Sano is implementing an Integral Chagas Program in a rural area of the Argentinean Gran Chaco Region since 2002. The objective of this study was to analyze both, temporal and spatial variation of infestation indices and their relation to the actions of the Program and environmental variables as land and vegetation cover changes, during a 5 year intervention period (2010-2014). Triatoma infestans infestation data from five rural localities from the Province of Santiago del Estero (Argentina) was analyzed in order to detect spatial aggregation. Differences in control effectiveness were observed between the peridomicile and intradomicile: infestation indices were higher in the peridomicile, recurrent infestation was present only in the peridomicile while low level infestation clusters were absent in the peridomicile. Cluster zones with low intradomestic infestation had larger proportions of bare soil and thin vegetation. In contrast, cluster zones with high intradomestic infestation had higher forest vegetation proportions and smaller cultivated area proportions. Spatial statistics analysis detected differences in cluster patterns between intra and peridomestic infestation suggesting that control actions should be based on geographical areas and not on political units. This work brings together different approaches to analyze infestation levels at the fine spatial scale, which could be used as a base for risk spatial stratification.

Temporal Dynamics and Spatial Patterns of Aedes aegypti Breeding Sites, in the Context of a Dengue Control Program in Tartagal (Salta Province, Argentina).

BACKGROUND: Since 2009, Fundación Mundo Sano has implemented an Aedes aegypti Surveillance and Control Program in Tartagal city (Salta Province, Argentina). The purpose of this study was to analyze temporal dynamics of Ae. aegypti breeding sites spatial distribution, during five years of samplings, and the effect of control actions over vector population dynamics. METHODOLOGY/PRINCIPAL FINDINGS: Seasonal entomological (larval) samplings were conducted in 17,815 fixed sites in Tartagal urban area between 2009 and 2014. Based on information of breeding sites abundance, from satellite remote sensing data (RS), and by the use of Geographic Information Systems (GIS), spatial analysis (hotspots and cluster analysis) and predictive model (MaxEnt) were performed. Spatial analysis showed a distribution pattern with the highest breeding densities registered in city outskirts. The model indicated that 75% of Ae. aegypti distribution is explained by 3 variables: bare soil coverage percentage (44.9%), urbanization coverage percentage(13.5%) and water distribution (11.6%). CONCLUSIONS/SIGNIFICANCE: This results have called attention to the way entomological field data and information from geospatial origin (RS/GIS) are used to infer scenarios which could then be applied in epidemiological surveillance programs and in the determination of dengue control strategies. Predictive maps development constructed with Ae. aegypti systematic spatiotemporal data, in Tartagal city, would allow public health workers to identify and target high-risk areas with appropriate and timely control measures. These tools could help decision-makers to improve health system responses and preventive measures related to vector control.

The peri-urban interface and house infestation with Triatoma infestans in the Argentine Chaco: an underreported process?

Peri-urban infestations with triatomine bugs, their sources and their dynamics have rarely been investigated. Here, we corroborated the reported occurrence of Triatoma infestans in a peri-urban area and in neighbouring rural houses in Pampa del Indio, in the Argentine Chaco, and identified its putative sources using spatial analysis and demographic questionnaires. Peri-urban householders reported that 10% of their premises had triatomines, whereas T. infestans was collected by timed manual searches or community-based surveillance in only nine (3%) houses. Trypanosoma cruzi-infected T. infestans and Triatoma sordida were collected indoors only in peri-urban houses and were infected with TcV and TcI, respectively. The triatomines fed on chickens, cats and humans. Peri-urban infestations were most frequent in a squatter settlement and particularly within the recently built mud houses of rural immigrants, with large-sized households, more dogs and cats and more crowding. Several of the observed infestations were most likely associated with passive bug transport from other sources and with active bug dispersal from neighbouring foci. Thus, the households in the squatter settlement were at a greater risk of bug invasion and colonisation. In sum, the incipient process of domestic colonisation and transmission, along with persistent rural-to-urban migratory flows and unplanned urbanisation, indicate the need for active vector surveillance and control actions at the peri-urban interface of the Gran Chaco.

The peri-urban interface and house infestation with Triatoma infestans in the Argentine Chaco: an underreported process?

Peri-urban infestations with triatomine bugs, their sources and their dynamics have rarely been investigated. Here, we corroborated the reported occurrence of Triatoma infestans in a peri-urban area and in neighbouring rural houses in Pampa del Indio, in the Argentine Chaco, and identified its putative sources using spatial analysis and demographic questionnaires. Peri-urban householders reported that 10% of their premises had triatomines, whereas T. infestans was collected by timed manual searches or community-based surveillance in only nine (3%) houses. Trypanosoma cruzi-infected T. infestans and Triatoma sordida were collected indoors only in peri-urban houses and were infected with TcV and TcI, respectively. The triatomines fed on chickens, cats and humans. Peri-urban infestations were most frequent in a squatter settlement and particularly within the recently built mud houses of rural immigrants, with large-sized households, more dogs and cats and more crowding. Several of the observed infestations were most likely associated with passive bug transport from other sources and with active bug dispersal from neighbouring foci. Thus, the households in the squatter settlement were at a greater risk of bug invasion and colonisation. In sum, the incipient process of domestic colonisation and transmission, along with persistent rural-to-urban migratory flows and unplanned urbanisation, indicate the need for active vector surveillance and control actions at the peri-urban interface of the Gran Chaco.

New records of mosquito species in the provinces of Chaco and Formosa, Argentina.

Seven mosquito species are recorded for the 1st time for northeastern Argentina: Culex (Melanoconion) albinensis, Cx. (Mel.) elevator, Cx. (Mel.) intrincatus, and Cx. (Mel.) serratimarge for Formosa Province, and Sabethes (Peytonulus) undosus, Sa. (Sabethinus) melanoninphe, and Toxorhynchites (Lynchiella) theobaldi for Chaco Province. The geographical distribution of these species is extended to northeastern Argentina, and the number of species increases to 97 and 75 for the provinces of Chaco and Formosa, respectively.

Water use practices limit the effectiveness of a temephos-based Aedes aegypti larval control program in Northern Argentina.

BACKGROUND: A five-year citywide control program based on regular application of temephos significantly reduced Aedes aegypti larval indices but failed to maintain them below target levels in Clorinda, northern Argentina. Incomplete surveillance coverage and reduced residuality of temephos were held as the main putative causes limiting effectiveness of control actions. METHODOLOGY: The duration of temephos residual effects in household-owned water-holding tanks (the most productive container type and main target for control) was estimated prospectively in two trials. Temephos was applied using spoons or inside perforated small zip-lock bags. Water samples from the study tanks (including positive and negative controls) were collected weekly and subjected to larval mortality bioassays. Water turnover was estimated quantitatively by adding sodium chloride to the study tanks and measuring its dilution 48 hs later. PRINCIPAL FINDINGS: The median duration of residual effects of temephos applied using spoons (2.4 weeks) was significantly lower than with zip-lock bags (3.4 weeks), and widely heterogeneous between tanks. Generalized estimating equations models showed that bioassay larval mortality was strongly affected by water type and type of temephos application depending on water type. Water type and water turnover were highly significantly associated. Tanks filled with piped water had high turnover rates and short-lasting residual effects, whereas tanks filled with rain water showed the opposite pattern. On average, larval infestations reappeared nine weeks post-treatment and seven weeks after estimated loss of residuality. CONCLUSIONS: Temephos residuality in the field was much shorter and more variable than expected. The main factor limiting temephos residuality was fast water turnover, caused by householders' practice of refilling tanks overnight to counteract the intermittence of the local water supply. Limited field residuality of temephos accounts in part for the inability of the larval control program to further reduce infestation levels with a treatment cycle period of 3 or 4 months.