Chagas disease in the context of the 2030 agenda: global warming and vectors.

The 2030 Agenda for Sustainable Development is a plan of action for people, planet and prosperity. Thousands of years and centuries of colonisation have passed the precarious housing conditions, food insecurity, lack of sanitation, the limitation of surveillance, health care programs and climate change. Chagas disease continues to be a public health problem. The control programs have been successful in many countries in reducing transmission by T. cruzi; but the results have been variable. WHO makes recommendations for prevention and control with the aim of eliminating Chagas disease as a public health problem. Climate change, deforestation, migration, urbanisation, sylvatic vectors and oral transmission require integrating the economic, social, and environmental dimensions of sustainable development, as well as the links within and between objectives and sectors. While the environment scenarios change around the world, native vector species pose a significant public health threat. The man-made atmosphere change is related to the increase of triatomines' dispersal range, or an increase of the mobility of the vectors from their sylvatic environment to man-made constructions, or humans getting into sylvatic scenarios, leading to an increase of Chagas disease infection. Innovations with the communities and collaborations among municipalities, International cooperation agencies, local governmental agencies, academic partners, developmental agencies, or environmental institutions may present promising solutions, but sustained partnerships, long-term commitment, and strong regional leadership are required. A new world has just opened up for the renewal of surveillance practices, but the lessons learned in the past should be the basis for solutions in the future.

Different profiles and epidemiological scenarios: past, present and future.

The multiplicity of epidemiological scenarios shown by Chagas Disease, derived from multiple transmission routes of the aetiological agent, occurring on multiple geo-ecobiosocial settings determines the complexity of the disease and reveal the difficulties for its control. From the first description of the link between the parasite, the vector and its domestic habitat and the disease that Carlos Chagas made in 1909, the epidemiological scenarios of the American Trypanosomiasis has shown a dynamic increasing complexity. These scenarios changed with time and geography because of new understandings of the disease from multiple studies, because of policies change at the national and international levels and because human movements brought the parasite and vectors to new geographies. Paradigms that seemed solid at a time were broken down, and we learnt about the global dispersion of Trypanosoma cruzi infection, the multiplicity of transmission routes, that the infection can be cured, and that triatomines are not only a health threat in Latin America. We consider the multiple epidemiological scenarios through the different T. cruzi transmission routes, with or without the participation of a Triatominae vector. We then consider the scenario of regions with vectors without the parasite, to finish with the consideration of future prospects.

Chagas disease ecoepidemiology and environmental changes in northern Minas Gerais state, Brazil.

BACKGROUND: Triatoma sordida and Triatoma pseudomaculata are frequently captured triatomine species in the Brazilian savannah and caatinga biomes, respectively, and in Brazilian domiciles. OBJECTIVES: This study identified eco-epidemiological changes in Chagas disease in northern Minas Gerais state, Brazil, and considered the influence of environmental shifts and both natural and anthropogenic effects. METHODS: Domicile infestation and Trypanosoma cruzi infection rates were obtained from triatomines and sylvatic reservoirs during the following two time periods: the 1980s and 2007/2008. Entomological and climatic data with land cover classification derived from satellite imagery were integrated into a geographic information system (GIS), which was applied for atmospheric correction, segmentation, image classification, and mapping and to analyse data obtained in the field. Climatic data were analysed and compared to land cover classifications. RESULTS: A comparison of current data with data obtained in the 1980's showed that T. sordida colonised domiciliary areas in both periods, and that T. pseudomaculata did not colonise these areas. There was a tendency toward a reduction in T. cruzi infection rates in sylvatic reservoirs, and of triatomines captured in both households and in the sylvatic environment. T. sordida populations have reduced in the sylvatic environment, while T. pseudomaculata showed an expanding trend in the region compared to counts observed in the 1980's in the sylvatic environment. This may be related to high deforestation rates as well as gradual increases in land surface temperature (LST) and temperatures along the years. MAIN CONCLUSIONS: Our results suggest a geographical expansion of species into new biomes as a result of anthropogenic and climatic changes that directly interfere with the reproductive and infection processes of vectors.

Spatial distribution of triatomines in domiciles of an urban area of the Brazilian Southeast Region.

Reports of triatomine infestation in urban areas have increased. We analysed the spatial distribution of infestation by triatomines in the urban area of Diamantina, in the state of Minas Gerais, Brazil. Triatomines were obtained by community-based entomological surveillance. Spatial patterns of infestation were analysed by Ripley's K function and Kernel density estimator. Normalised difference vegetation index (NDVI) and land cover derived from satellite imagery were compared between infested and uninfested areas. A total of 140 adults of four species were captured (100 Triatoma vitticeps, 25 Panstrongylus geniculatus, 8 Panstrongylus megistus, and 7 Triatoma arthurneivai specimens). In total, 87.9% were captured within domiciles. Infection by trypanosomes was observed in 19.6% of 107 examined insects. The spatial distributions ofT. vitticeps, P. geniculatus, T. arthurneivai, and trypanosome-positive triatomines were clustered, occurring mainly in peripheral areas. NDVI values were statistically higher in areas infested by T. vitticeps and P. geniculatus. Buildings infested by these species were located closer to open fields, whereas infestations of P. megistus and T. arthurneivai were closer to bare soil. Human occupation and modification of natural areas may be involved in triatomine invasion, exposing the population to these vectors.

Association between environmental gradient of anthropization and phenotypic plasticity in two species of triatomines.

BACKGROUND: Triatoma garciabesi and T. guasayana are considered secondary vectors of Trypanosoma cruzi and frequently invade rural houses in central Argentina. Wing and head structures determine the ability of triatomines to disperse. Environmental changes exert selective pressures on populations of both species, promoting changes in these structures that could have consequences for flight dispersal. The aim of this study was to investigate the relationship between a gradient of anthropization and phenotypic plasticity in flight-related traits. METHODS: The research was carried out in Cruz del Eje and Ischilín departments (Córdoba, Argentina) and included 423 individuals of the two species of triatomines. To measure the degree of anthropization, a thematic map was constructed using supervised classification, from which seven landscapes were selected, and nine landscape metrics were extracted and used in a hierarchical analysis. To determine the flight capacity and the invasion of dwellings at different levels of anthropization for both species, entomological indices were calculated. Digital images of the body, head and wings were used to measure linear and geometric morphometric variables related to flight dispersion. One-way ANOVA and canonical variate analysis (CVA) were used to analyze differences in size and shape between levels of anthropization. Procrustes variance of shape was calculated to analyze differences in phenotypic variation in heads and wings. RESULTS: Hierarchical analysis was used to classify the landscapes into three levels of anthropization: high, intermediate and low. The dispersal index for both species yielded similar results across the anthropization gradient. However, in less anthropized landscapes, the density index was higher for T. garciabesi. Additionally, in highly anthropized landscapes, females and males of both species exhibited reduced numbers. Regarding phenotypic changes, the size of body, head and wings of T. garciabesi captured in the most anthropized landscapes was greater than for those captured in less anthropized landscapes. No differences in body size were observed in T. guasayana collected in the different landscapes. However, males from highly anthropized landscapes had smaller heads and wings than those captured in less anthropized landscapes. Both wing and head shapes varied between less and more anthropogenic environments in both species. CONCLUSIONS: Results of the study indicate that the flight-dispersal characteristics of T. garciabesi and T. guasayana changed in response to varying degrees of anthropization.

Socio-environmental factors associated with the occurrence of triatomines (Hemiptera: Reduviidae) in an endemic municipality in northern Minas Gerais, Brazil.

Triatomines are the vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. The study aimed to evaluate the association between sociodemographic and environmental factors, and changes in land use and cover, with the occurrence and abundance of triatomines by census sectors in an endemic municipality of northern Minas Gerais, Brazil. The study was conducted in Montes Claros, located in the north of Minas Gerais, Brazil. The entomological data used in the study were collected by active surveillance in the rural area from 2015 to 2019 and by passive surveillance in the urban area from 2009 to 2019. Data on sociodemographic and environmental factors and changes in land use and land cover were obtained from the urban and rural census sectors. A total of 1404 triatomines, belonging to eight species, were captured in domiciles in the rural area (2015-2019) and 277 triatomines in domiciles in the urban area (2009-2019) of the municipality of Montes Claros. The variables the number of domiciles, household economic income, pavement, NDVI, deforestation, unchanged, and anthropic proved to be positively associated with the occurrence and/or number of triatomines in census sectors, within the models. The occurrence of triatomines in the domestic environment of the municipality of Montes Claros should be considered a public health problem, as it suggests a potential risk of establishment and transmission of T. cruzi to domestic animals, farm animals, and humans.

Potential sources of Triatoma infestans reinfesting peridomiciles identified by morphological characterization in Los Llanos, La Rioja, Argentina.

The presence of Triatoma infestans in habitats treated with insecticides constitutes a frequent problem in endemic areas. Basing our study on the hypothesis that descendants of a residual population should be more similar to the pre-treatment population than to any other, we compared the indications of two quantitative morphological approaches. This study seeks to find the origin of 247 T. infestans from three populations found in two chicken coops and a goat corral after treatment with insecticides. The results obtained by quantitative morphology suggest that the T. infestans found between three-34 months after the application of insecticides formed mixed populations with insects derived from residual foci and neighbouring habitats. Our analyses also showed the presence of a phenotype which does not resemble neither the pre-treatment phenotype nor the one from neighbouring populations, suggesting the presence of a particular post-treatment phenotype. The heads size showed some variations in males from different populations and remained unchanged in females, which reinforces the hypothesis of an intraspecific competition for food with priority for females. This article presents, for the first time, the combined analysis of geometric morphometry of heads and antennal phenotypes to identify the composition of reinfesting populations.

New structures for goat corrals to control peridomestic populations of Triatoma infestans (Hemiptera: Reduviidae) in the Gran Chaco of Argentina.

Goat production is an important economic activity for rural communities in the Gran Chaco of Argentina. Goat corrals are important for the survival of peridomestic populations of Triatoma infestans. This study evaluated the impact of modifying the traditional structure of goat corrals on T. infestans populations and goat productivity in the region of Los Llanos (La Rioja). Thirty-nine experimental corrals were constructed and 57 traditional corrals were used as controls. We evaluated the infestations of the control and experimental corrals for five years following construction of the structures. The results showed that the new structures did not prevent the colonization, although it enhanced the detection of infestation at low densities of T. infestans. No significant difference was found in T. infestans population abundance between control and experimental corrals, probably because of the different detectability in the two types of structures, especially among the small nymphs. Although goat productivity average was higher in experimental than in control corrals, no significant difference was found because of high variability. The new structures can be used as a complement to promote the development of rural communities. Acceptability and adoption of the new corrals by the owners was high, as the enclosures offered better protection for the goats, increased growth of kids and facilitated herd handling.

Influence of anthropic changes and environmental characteristics on the occurrence of Tegumentary Leishmaniasis in Montes Claros, Minas Gerais, Brazil, between 2012 and 2019.

This is an ecological study that investigated the influence of environmental, socioeconomic characteristics and changes in land use and cover on the occurrence of Tegumentary Leishmaniasis (TL) in the city of Montes Claros. The relationships between the number of cases of TL, which occurred between 2012 and 2019, in each census sector and the standardized covariates (Number of properties, altitude, Brazilian Deprivation Index, Normalized Difference Vegetation Index (NDVI), proportion of sector (PS) deforested, PS that underwent other anthropic alterations and unaltered PS) were evaluated with ecological Bayesian Models. Four multivariate models were constructed, with similar quality of adjustments, but Model 1 was the most parsimonious. Model 1 revealed that for each one-unit increase of standard deviation (SD) in the log of the number of properties, at the altitude and root of the deforested PS, corresponds to an increase of 44%, 34% and 24.5% in the number of cases of TL, respectively. The variable NDVI, included in models 3 and 4, was positively associated with the increase in the number of TL cases, being that for each one-unit increase in the NDVI was verified an increase of 21.3% and 20.2% respectively in the models. This study showed that the spatial distribution of TL cases in the city of Montes Claros occurs in a heterogeneous way and our findings support the hypothesis that socio-environmental characteristics and deforestation influence the occurrence of this disease in the studied area. Thus, these factors must be considered for the development of disease control strategies.

The residual efficacy of a cypermethrin pour-on formulation applied on goats on the mortality and blood intake of Triatoma infestans.

Triatoma infestans is the main vector of Trypanosoma cruzi, the aetiological agent of Chagas disease in the Gran Chaco region of South America. As a frequent blood meal source for triatomine bugs, domestic goats play a key role in the eco-epidemiology of Chagas disease. The aim of this study was to evaluate the mortality and blood intake of T. infestans fed on goats that had been treated with different doses of pour-on insecticide. Third-instar nymphs were fed on goats that had been treated with 0 cc, 5 cc, 10 cc or 15 cc of a pour-on formulation of cypermethrin. The exposure of T. infestans to animals treated at different post-application intervals revealed a residual activity of the insecticide. The mortality rate in the treated groups was higher than in the control groups until 30 days post-insecticide application (p = 0.03), except in the group treated with 5 cc, in which no mortality was detected after seven days of insecticide application. Rainfall affected the triatomicide effect, reducing the time of residual activity. The cypermethrin pour-on treatment decreased the blood intake of T. infestans. Thirty days after the cypermethrin application, nymph mortality was 16% (± 13) with both doses (10 cc and 15 cc). The 15 cc dose did not result in higher insect mortality or increased persistence compared to the 10 cc dose.

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.

Effects of fipronil on dogs over Triatoma infestans, the main vector of Trypanosoma cruzi, causative agent of Chagas disease.

Chagas disease is the most important endemic disease in Latin America, mainly transmitted by Triatoma infestans in the Southern Cone countries of South America. Dogs are one of the main domestic reservoirs of Trypanosoma cruzi, the etiological agent of Chagas disease. The presence of dogs in rural households of endemic areas significantly increases the likelihood of the vectorial transmission of the parasite. We studied the mortality and blood intake of T. infestans exposed to dogs treated with different doses and formulations of fipronil. Two doses, two formulations, and different distances to the application point of fipronil were compared. Third instar nymphs of T. infestans were fed at different time intervals after the insecticide application up to 45 days post-application. No significant difference was found between the blood intake of nymphs fed on control and treated dogs with different doses and formulations (p > 0.05). The spray formulation showed lower effect and persistence than the spot-on formulation. The mortality rate caused by the spot-on formulation in the 26.8-mg active ingredient (a.i.)/kg dose was higher (48%) than with the 13.4-mg a.i./kg dose (25%), 24 h after the insecticide application. The effect was highly heterogeneous among replicates of the same treatment. The mortality rate of nymphs fed over the point of the insecticide application was higher than the mortality of nymphs fed over places 12 cm apart from the fipronil application point, suggesting that the distribution of fipronil over the dog body is lower than the needed one to obtain a persistent triatomicide effect.

Ecomorphological variation of the Triatoma guasayana wing shape in semi-arid Chaco region.

Triatoma guasayana (Hemiptera, Reduviidae), considered a secondary vector of Chagas disease, invades rural dwellings through flight dispersal during the warm season in semi-arid Chaco of Argentina. The objective of this study was to define and compare morphometrics features in the relative body size and wing shape of T. guasayana related to temperature and rainfall between spring, summer and end of summer. A total of 188 adults were collected in rural communities in the northwest of the province of Córdoba (central Argentina). Relative body size [body length (mm) / wing length (mm)] and 11 landmarks on the right wing were recorded. The temperature ( °C) and precipitation (mm) data were extracted from the MODIS sensor and Terra Climate dataset, respectively. Correlations between climatic variables and morphological variation were analyzed using Partial Least Square (PLS). Males at the end of summer were smaller than those at spring or summer (F = 4.48; df = 2; p = 0.01), whereas females were similar in relative body size at all seasons (F = 0.76; df = 2; p = 0.47). The PLS in males showed a correlation between wing shape and temperature (r = 0.48; p = 0.03) and precipitation (r = 0.50; p = 0.02) while in females only the temperature was the correlation significant (r = 0.35; p = 0.03). Triatoma guasayana has elongated and thin wings in spring that become short and wide at the end of summer. The morphotype of early summer could allow sustained long-duration flights, while the morphotype of end of summer would be related to short flights, correlated with the dispersive behavior of the species. The results in this study suggest that wing morphology of T. guasayana has phenotypic plasticity, and that temperature and rainfall could be considered modulator factors during the developmental stage.

Variability of the susceptibility to deltamethrin in Triatoma infestans: the female factor.

We analyzed the variability of susceptibility to deltamethrin in putatively susceptible Triatoma infestans Klug (Hemiptera: Reduviidae), and evaluated the sample size implications on the hypotheses used in the current World Health Organization protocol for the measure of insecticide resistance in Triatominae. Following the protocol, using topical application of deltamethrin to unfed first instar nymphs of T. infestans, we found that susceptibility showed significant differences between offspring from different females, a significant association with female age, and significant interaction female x female age. Considering individual female data, three patterns of nymphal mortality were identified: one showed a strong positive relation between nymphal mortality and their mother's age, another showed high mortality with low variability and the third showed intermediate mortality with high variability along female age. The analysis suggests revision of the World Health Organization protocol for resistance detection in Triatominae, not only to take into consideration the sources of variation in susceptibility, but also the effects of sample size in relation to the significance and power probabilities of the test.

Dispersal of Triatoma infestans and other Triatominae species in the arid Chaco of Argentina: flying, walking or passive carriage? The importance of walking females.

The aim of this paper was to analyse the active dispersal of Triatoma infestans and the role of chickens as passive carriers of this insect in peridomestic areas of La Rioja, Argentina. To measure active dispersal, monthly catches were made on six consecutive nights for five months (in the warm season) using light traps (for flying insects) and sticky dispersal barriers (for walking insects). The nutritional and reproductive states of adults were evaluated. Over the course of the sampling period, a total of eight flying adults, six walking nymphs and 10 walking adults of the species T. infestans were captured, as well as specimens of Triatoma guasayana, Triatoma eratyrusiformis and Triatoma platensis. Our data demonstrate for the first time that females of T. infestans can disperse by walking. This may be an adaptive strategy because it allows them to move with eggs and/or with good blood reserves, which are not possible when flying. All flying and walking individuals of both genders were of an appropriate physiological state that would allow for colonisation of the target habitat. However, manual inspection of 122 chickens suggests that it is unlikely that these animals passively transport T. infestans. Finally, the dispersal activity of T. infestans was compared with other triatomines using a dispersion index.

[Climate change and vector-borne diseases in Argentina]. / Cambio climático y enfermedades transmitidas por vectores en Argentina.

Vector-borne diseases (VBDs) continue to pose a challenge to the efforts of public health agencies by increasing their impact on the health of the affected communities. The common feature of VBDs is that the only way of preventing them is by avoiding the contact between vectors and humans. There are no vaccines, and they will not be available shortly as tools for prevention and control in Argentina. Although dengue outbreaks attracted the attention of mass media from 2009, other VBDs have been affecting public health in Argentina for many decades, as Chagas disease and leishmaniasis. Over these, and others that could potentially settle in the national territory (West Nile, Lyme, etc.), there are repeated mass media claims and political declarations justifying their increase because of climate changes. The argument asserts that the "tropicalization" of the climate in temperate regions promotes the installation of VBDs in areas previously unfavorable for them. Although much evidence exists showing that the climate is changing, there is very little evidence that the climate is the main factor promoting the increase of VBDs. In this article, the influence of the so-called climate change on the situation of disease vectors in Argentina (with emphasis on triatomines) and vector control activities implemented by governmental public health agencies are discussed.

Las enfermedades transmitidas por vectores (ETVs) continúan siendo un desafío para los esfuerzos de agencias de salud pública, ya que mantienen o están aumentando su impacto sobre la salud de las comunidades afectadas. La característica común de las ETVs es que la única manera de prevenir exitosamente nuevas infecciones es evitar el contacto entre vectores y humanos. No existen vacunas y no existirán en un futuro previsible para las principales ETVs que afectan la salud pública en Argentina. Aunque las epidemias de dengue desde 2009 atrajeron la atención mediática, otras ETVs, tales como Chagas o leishmaniasis, afectan la salud pública en Argentina desde hace décadas. Sobre ellas, y otras que potencialmente podrían instalarse en el territorio nacional (West Nile, Lyme, etc) hay repetidas referencias mediáticas que explican su recrudecimiento por el cambio climático. El argumento se basa en que la "tropicalización" del clima en regiones templadas promueve la instalación de ETVs en áreas previamente no favorables para ellas. Aunque existen muchas evidencias de que el clima está cambiando, son pocas las evidencias de que sea el clima el principal factor que promueve el recrudecimiento de las ETVs en Argentina. En este artículo, se discute la situación de los vectores de enfermedades en Argentina (con énfasis en triatominos), su vinculación con el llamado cambio climático y las actividades de control de vectores implementados por agencias gubernamentales de salud pública.

Triatominae of the semi-arid Chaco in central Argentina.

The epidemiological scenario in central Argentinian Chaco region shows persistence of Triatoma infestans domestic populations in endemic areas, with control interventions historically affected by the economic instability of the region. Considering this situation, we aimed to (i) update the information regarding to the diversity of triatomines present in domestic, peridomestic and sylvatic environments in departments historically endemic of the Chaco region, (ii) to report the occurrence of secondary vectors of Chagas disease invading domestic environments and (iii) to discuss the possible sources of dispersal of these sylvatic species towards anthropic habitats. Between November 2017 and March 2020, we visited fourteen rural communities of northwest Córdoba province (central Argentina). Entomological data were collected through community vector surveillance in domiciles, active search in peridomiciles and the use of light and yeast traps in sylvatic environments. Seven Triatominae species were captured invading domiciles (T. guasayana, T. garciabesi, T. platensis, T. delpontei, T. breyeri, Panstrongylus guentheri and T. infestans). T. guasayana and T. garciabesi were the species with the highest number of captures. The 32% of the peridomiciles registered infestation with T. infestans (n â€‹= 355), mostly in chicken coops and goat pens. In sylvatic environments, T. garciabesi, T. guasayana, T. infestans and P. guentheri were collected. Only one adult specimen of T. infestans was positive for the presence of Trypanosoma cruzi. Our results suggest that the persistence of T. infestans populations in peridomiciles continues to be a serious challenge for control programs, whereas the finding of secondary vectors of Chagas disease actively invading domiciles emphasizes the need to implement new strategies for entomological surveillance.

Effect of habitat fragmentation on rural house invasion by sylvatic triatomines: A multiple landscape-scale approach.

After the decrease of the relative importance of Triatoma infestans, a number of studies reported the occurrence of sylvatic triatomines dispersing actively to domestic environments in the dry western Chaco Region of Argentina. Anthropic modification of the landscape is mentioned as one of the main causes of the increase in domicile invasion. The aim of this study was to describe the occurrence and frequency of sylvatic triatomines invading rural houses, and to evaluate the effect of habitat fragmentation and other ecological factors on the invasion of rural houses in central Argentina. We hypothesized that the decrease in food sources and the loss of wild ecotopes, as a consequence of habitat fragmentation, increase the chances of invasion by triatomines. The entomological data was collected by community-based vector surveillance during fieldwork carried out between 2017-2020, over 131 houses located in fourteen rural communities in the northwest of Córdoba Province (central Argentina). We used generalized linear models to evaluate the effect of (i) the environmental anthropic disturbance in the study area, (ii) the composition and configuration of the landscape surrounding the house, (iii) the spatial arrangement of houses, (iv) and the availability of artificial refuges and domestic animals in the peridomicile, on house invasion by triatomines. We report the occurrence of seven species of triatomines invading rural houses in the study area -T. infestans, T. guasayana, T. garciabesi, T. platensis, T. delpontei, T. breyeri and P. guentheri-. Study data suggest that invasion by triatomines occurs with higher frequency in disturbed landscapes, with houses spatially isolated and in proximity to subdivided fragments of forest. The availability of domestic refuges in the peridomestic structures as well as the presence of a higher number of domestic animals increase the chances of invasion by triatomines.

The effects of cypermethrin pour-on and piperonyl butoxide on Triatoma infestans under laboratory conditions.

The effect of exposing Triatoma infestans to chickens treated with cypermethrin pour-on combined with piperonyl butoxide (PBO) was studied. Four groups of treated chickens and one control group were used. Each treatment received 1 or 2 ml of the cypermethrin formulation with and without PBO. Independent groups of nymphs were fed 1, 7, 15, 30, and 45 d after the treatment application. Blood intake was estimated after each feeding occasion. Up to 15 d after the pour-on application, high mortality was observed in all nymphs fed on treated chickens (> 93% +/- 12), and lower than the nymphs of the control group (< 33% +/- 15). After 30 d of the pour-on application, there was significantly different mortality between the treatment with 1 ml (80% +/- 9) and 2 ml (> 96% +/- 5); no difference was observed between groups with or without PBO addition. After 45 d of the pour-on application, the treatments did not show significant differences (77% +/- 7), although all treatments showed higher mortality than the control group (10% +/- 9). Up to 45 d after the pour-on application, blood intake by nymphs exposed to treated chickens (0.85 +/- 0.96 mg/nymph) was lower than blood intake by nymphs exposed to control chickens (6.7 +/- 5 mg/nymph). This study shows that cypermethrin pour-on produces high mortality and reduces the blood intake of third-instar nymphs of T. infestans up to 45 d after the insecticide application to chickens. PBO did not produce a detectable effect.

Residual effect of a micro-encapsulated formulation of organophosphates and piriproxifen on the mortality of deltamethrin resistant Triatoma infestans populations in rural houses of the Bolivian Chaco region.

The Bolivian Chaco is part of the endemic region of Chagas disease and an area where pyrethroid resistant Triatoma infestans (Hemiptera: Reduviidae) populations has been reported. The World Health Organization identified these resistant populations as an important focus for research. The objective of this study was to evaluate the residual effect of a micro-encapsulated formulation containing organophosphate active ingredients and a juvenile hormone analogue (Inesfly 5A IGR) on the mortality of T. infestans. Studies took place in rural houses of the Bolivian Chaco that were treated up to 34 months before and evaluated the susceptibility to pyrethroids of the offspring of field collected insects. Thirty houses were randomly selected within three communities to carry out wall bio-assays with T. infestans nymphs. Mortality was recorded 24, 48 and 72 h after wall contact. Eggs laid by females collected in the area were used to obtain first-instar nymphs and carry out pyrethroid susceptibility tests. The wall bio-assays showed that the micro-encapsulated insecticide eliminates T. infestans populations and produces detectable mortality of insects exposed to walls treated 34 months prior to the tests. The discriminant dose of deltamethrin (0.01 mg/mL) showed 65% nymph survival, whereas at the highest tested dose (1.0 mg/mL) 14% of the nymphs survived. These results show that Inesfly 5A IGR is an appropriate tool for the elimination of intradomestic and peridomestic populations of T. infestans resistant to pyrethroids.