First finding of melanic sylvatic Triatoma infestans (Hemiptera: Reduviidae) colonies in the Argentine Chaco

Relationship between genetic diversity and morpho-functional characteristics of flight-related traits in Triatoma garciabesi (Hemiptera: Reduviidae)

BACKGROUND

Triatoma garciabesi, a potential vector of the parasitic protozoan Trypanosoma cruzi, which is the causative agent of Chagas disease, is common in peridomestic and wild environments and found throughout northwestern and central Argentina, western Paraguay and the Bolivian Chaco. Genetic differentiation of a species across its range can help to understand dispersal patterns and connectivity between habitats. Dispersal by flight is considered to be the main active dispersal strategy used by triatomines. In particular, the morphological structure of the hemelytra is associated with their function. The aim of this study was to understand how genetic diversity is structured, how morphological variation of dispersal-related traits varies with genetic diversity and how the morphological characteristics of dispersal-related traits may explain the current distribution of genetic lineages in this species.

METHODS

Males from 24 populations of T. garciabesi across its distribution range were examined. The cytochrome c oxidase I gene (coI) was used for genetic diversity analyses. A geometric morphometric method based on landmarks was used for morpho-functional analysis of the hemelytra. Centroid size (CS) and shape of the forewing, and contour of both parts of the forewing, the head and the pronotum were characterised. Length and area of the forewing were measured to estimate the aspect ratio.

RESULTS

The morphometric and phylogenetic analysis identified two distinct lineages, namely the Eastern and Western lineages, which coincide with different ecological regions. The Eastern lineage is found exclusively in the eastern region of Argentina (Chaco and Formosa provinces), whereas the Western lineage is prevalent in the rest of the geographical range of the species. CS, shape and aspect ratio of the hemelytra differed between lineages. The stiff portion of the forewing was more developed in the Eastern lineage. The shape of both portions of the hemelytra were significantly different between lineages, and the shape of the head and pronotum differed between lineages.

CONCLUSIONS

The results provide preliminary insights into the evolution and diversification of T. garciabesi. Variation in the forewing, pronotum and head is congruent with genetic divergence. Consistent with genetic divergence, morphometry variation was clustered according to lineages, with congruent variation in the size and shape of the forewing, pronotum and head.

The Pampa del Indio project: District-wide quasi-elimination of Triatoma infestans after a 9-year intervention program in the Argentine Chaco

BACKGROUND

The elimination of Triatoma infestans, the main domestic vector of Trypanosoma cruzi, is lagging behind expectations in the Gran Chaco region. We implemented an insecticide-based intervention program and assessed its long-term effects on house infestation and bug abundance in a resource-constrained municipality (Pampa del Indio, northeastern Argentina) inhabited by creole and the Qom indigenous people (2007-2016). Key questions were whether district-wide data integration revealed patterns concealed at lower spatial levels; to what extent preintervention infestation and pyrethroid resistance challenged the effectiveness of insecticide-based control efforts, and how much control effort was needed to meet defined targets.

METHODS

Supervised vector control teams i) georeferenced every housing unit at baseline (1,546); ii) evaluated house infestation using timed-manual searches with a dislodging aerosol across four rural areas designated for district-wide scaling up; iii) sprayed with pyrethroid insecticide 92.7% of all houses; iv) periodically monitored infestation and promoted householder-based surveillance, and v) selectively sprayed the infested houses, totaling 1,823 insecticide treatments throughout the program.

RESULTS

Baseline house infestation (mean, 26.8%; range, 14.4-41.4%) and bug abundance plummeted over the first year postintervention (YPI). Timed searches at baseline detected 61.4-88.0% of apparent infestations revealed by any of the methods used. Housing dynamics varied widely among areas and between Qom and creole households. Preintervention triatomine abundance and the cumulative frequency of insecticide treatments were spatially aggregated in three large clusters overlapping with pyrethroid resistance, which ranged from susceptible to high. Persistent foci were suppressed with malathion. Aggregation occurred mainly at house compound or village levels. Preintervention domestic infestation and abundance were much greater in Qom than in creole households, whereas the reverse was recorded in peridomestic habitats. House infestation, rare (1.9-3.7%) over 2-6 YPI, averaged 0.66% (95% confidence interval, 0.28-1.29%) at endpoint.

CONCLUSIONS

Upscale integration revealed multiple coupled heterogeneities (spatial, sociodemographic and biological) that reflect large inequalities, hamper control efforts, and provide opportunities for targeted, sustainable disease control. High-coverage, professional insecticide spraying combined with systematic surveillance-and-response were essential ingredients to achieve the quasi-elimination of T. infestans within 5 YPI and concomitant transmission blockage despite various structural threats and constraints.

Atypical strategies for cuticle pigmentation in the blood-feeding hemipteran Rhodnius prolixus

Pigmentation in insects has been linked to mate selection and predator evasion, thus representing an important aspect for natural selection. Insect body color is classically associated to the activity of tyrosine pathway enzymes, and eye color to pigment synthesis through the tryptophan and guanine pathways, and their transport by ABC proteins. Among the hemiptera, the genetic basis for pigmentation in kissing bugs such as Rhodnius prolixus, that transmit Chagas disease to humans, has not been addressed. Here we report the functional analysis of R. prolixus eye and cuticle pigmentation genes. Consistent with data for most insect clades, we show that knockdown for yellow results in a yellow cuticle, while scarlet and cinnabar knockdowns display red eyes as well as cuticle phenotypes. In addition, tyrosine pathway aaNATpreto knockdown resulted in a striking dark cuticle that displays no color pattern or UV reflectance. In contrast, knockdown of ebony and tan, that encode NBAD branch tyrosine pathway enzymes, did not generate the expected dark and light brown phenotypes, respectively, as reported for other insects. We hypothesize that R. prolixus, which requires tyrosine pathway enzymes for detoxification from the blood diet, evolved an unusual strategy for cuticle pigmentation based on the preferential use of a color erasing function of the aaNATpreto tyrosine pathway branch. We also show that genes classically involved in the generation and transport of eye pigments regulate red body color in R. prolixus. This is the first systematic approach to identify the genes responsible for the generation of color in a blood-feeding hemiptera, providing potential visible markers for future transgenesis.

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

Background

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

Methodology/Principal findings

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

Conclusions/Significance

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

Trypanosoma cruzi Parasite Load Modulates the Circadian Activity Pattern of Triatoma infestans

Simple Summary

We studied the locomotor activity of one of the kissing bug species that transmit the Chagas disease-causing parasite in humans, which usually bites during the night. To date, no other reports researching its behavior take into account the amount of parasites inside the kissing bug; however, some studies have demonstrated that the presence of parasites modifies the activity of some kissing bug species. We recorded their movements in light and dark conditions after part of the insects fed on mammals that had the parasite and others fed on those that did not have the parasite. Later, their amounts of parasites were quantified. We found that, compared with insects with no parasites, kissing bugs with higher parasite amounts increase the number of times they move and the distance they travel, especially during daylight hours. This could imply that the insect increases its time searching for a food source when it is infected with a higher number of parasites, and this could increase the risk of transmission of the parasite to people by the kissing bug.

Abstract

American trypanosomiasis is a disease caused by the flagellate protozoan Trypanosoma cruzi, which is transmitted mainly in endemic areas by blood-sucking triatomine vectors. Triatoma infestans is the most important vector in the southern cone of South America, exhibiting a nocturnal host-seeking behavior. It has been previously documented that the parasite produces changes in some triatomine species, but this is the first time that the behavior of a vector has been evaluated in relation to its parasite load. After comparing the movement events and distance traveled of infected and non-infected T. infestans, we evaluated the change produced by different T. cruzi parasite loads on its circadian locomotor activity. We observed differences between infected and non-infected triatomines, and a significant relation between the parasite load and the increase in locomotor activity of T. infestans, which was accentuated during the photophase. This could have direct implications on the transmission of T. cruzi, as the increased movement and distance traveled could enhance the contact of the vector with the host, while increasing the predation risk for the vector, which could both constitute a risk for vectorial and oral transmission to mammals.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Insights into the evolution and dispersion of pyrethroid resistance among sylvatic Andean Triatoma infestans from Bolivia

Sylvatic populations of Triatoma infestans represent a challenge to Chagas disease control as they are not targeted by vector control activities and may play a key role in post-spraying house re-infestation. Understanding sylvatic foci distribution and gene flow between sylvatic and domestic populations is crucial to optimize vector control interventions and elucidate the development and spread of insecticide resistance. Herein, the genetic profiles of five Andean T. infestans populations from Bolivia with distinct insecticide susceptibility profiles were compared. Multilocus genotypes based on eight microsatellites and the DNA sequence of a fragment of the cytochrome B (cytB) gene were obtained for 92 individuals. CytB haplotypes were analyzed with previously reported Bolivian T. infestans haplotypes to evaluate putative historical gene flow among populations. Each specimen was also screened for two nucleotide mutations in the sodium channel gene (kdr), related to pyrethroid resistance (L1014 and L9251). Significant genetic differentiation was observed among all populations, although individuals of admixed origin were detected in four of them. Notably, the genetic profiles of adjacent domestic and sylvatic populations of Mataral, characterized by higher levels of insecticide resistance, support their common ancestry. Only one sylvatic individual from Mataral carried the kdr mutation L1014, suggesting that this mechanism is unlikely to cause the altered insecticide susceptibility observed in these populations. However, as the resistance mutation is present in the area, it has the potential to be selected under insecticidal pressure. Genetic comparisons of these populations suggest that insecticide resistance is likely conferred by ancient trait(s) in T. infestans sylvatic populations, which are capable of invading domiciles. These results emphasize the need for stronger entomological surveillance in the region, including early detection of house invasion, particularly post-spraying, monitoring for resistance to pyrethroids and the design of integrative control actions that consider sylvatic foci around domestic settings and their dispersion dynamics.

Characterization of melanic and non-melanic forms in domestic and peridomestic populations of Triatoma infestans (Hemiptera: Reduviidae)

BACKGROUND

Melanic (dark) morphs have been barely reported in peridomestic and sylvatic conditions for Triatoma infestans, the most important vector of Chagas disease in the Southern Cone of South America. Adults with dark and small yellow markings on the connexivum were collected after manual searches conducted by technical personnel in 62 domiciliary units in Cruz del Eje, Córdoba Province, Argentina. The last community-wide insecticide spraying campaign before the study had been conducted three years earlier. We investigated if there was a measurable color morph variation (melanic and non-melanic) in wings and connexivum; we determined infestation, distribution of melanic and non-melanic forms, and correspondence of colorimetric variation with variations in morphology (wing size and shape and body length), development (wing fluctuating asymmetry), physiology (nutritional status) or behaviour (flight initiation).

RESULTS

Forty-nine females, 54 males and 217 nymphs were collected in 24 domiciliary units. House infestation and colonization were 53% and 47%, respectively. Most of the T. infestans individuals (83.2%) were collected in chicken coops; intradomicile infestation was recorded in only one case. The chromatic cluster analysis showed two well-defined groups: melanic and non-melanic. The melanic group included 17 (35%) females and 25 (46%) males. Peridomestic infestation was lower for melanic than for non-melanic adults. Melanic morphs were collected in houses from several localities. Sexual dimorphisms were confirmed by morphometric measurements. Body length was large in melanic adults (P < 0.01 only for males). Differences between groups were significant for wing size and shape, but not for weight or weight/body length ratio. Melanic females and males showed significantly higher fluctuating asymmetry (FA) indices than their non-melanic counterparts.

CONCLUSIONS

This is the second report of melanic forms of T. infestans in domestic and peridomestic habitats in the Dry Chaco region of Argentina. Although non-melanic adults exhibited a higher infestation rate, melanic adults were widespread in the area and were collected in the infested domicile and in most types of peridomestic annexes. Differences in morphometric variables between groups might be due to different ecological adaptations. The higher FA levels observed in melanic individuals suggest a higher developmental instability and a selective advantage of non-melanic individuals in domestic and peridomestic habitats.

Improved detection of house infestations with triatomines using sticky traps: a paired-comparison trial in the Argentine Chaco

Background

We conducted a matched-pairs trial of three methods for detecting house infestation with triatominae bugs in a well-defined endemic rural area in the Argentine Chaco.

Methods

The three methods included a simple double-sided adhesive tape (ST) installed near host resting sites; timed-manual collections with a dislodging aerosol (TMC, the reference method used by vector control programmes), and householders’ bug notifications (HN). Triatomine infestations were evaluated in 103 sites of 54 houses, including domiciles, kitchens and storerooms.

Results

In domiciles where Triatoma infestans was collected, sensitivity of each single method decreased from 79% by ST and 77% by HN, to 57% by TMC, and increased to 92% when ST was combined with HN. In peridomestic kitchens and storerooms, TMC was relatively as sensitive as ST and significantly more sensitive than HN. On average, the number of bugs recovered by ST was 0.94 times that collected by TMC. The ST mainly collected early-instar nymphs whereas TMC yielded late (larger) stages. Triatomines caught by ST had significantly lower mean weight-to-length ratios and lower blood-feeding rates than those caught by TMC, suggesting the ST intercepted and trapped vectors seeking a blood meal host.

Conclusions

The ST may effectively replace TMC for detecting T. infestans in domiciles, and is especially apt for early detection of low-density domestic infestations in the frame of community-based surveillance or elimination programmes; decision making on whether an area should be targeted for full-coverage insecticide spraying, and to corroborate that extant conditions are compatible with the interruption of vector-borne transmission.

Genetic structure of the Chagas disease vector Triatoma infestans (Hemiptera: Reduviidae) based on nuclear and mitochondrial DNA sequences

In the present study, we analysed the genetic structure of Triatoma infestans populations with a phylogeographical approach using sequences of the mitochondrial NADH dehydrogenase subunit 5 (ND5) and the nuclear elongation factor-1 alpha (EF-1α) genes of bugs obtained from Argentina and Bolivia. Spatially circumscribed haplogroups were distinguished from the ND5 gene sequences, one distributed exclusively to the south of the studied area and, in agreement with the results from the EF-1α gene, one haplogroup limited to Bolivia and another to Morajú located in the Chaco region of Argentina. In both the ND5 and EF-1α networks, the most widespread haplogroup or allele group showed a star-like topology, which is compatible with a recent demographic expansion. The asymmetric historical gene flow detected from a population of the Chaco region towards Bolivia and the spatiotemporal phylogeographical reconstruction of lineage dispersal would support the hypothesis that postulates the Chaco biogeographical region as the area of origin for the species. However, additional studies with a broader sampling in the Andean region are needed to define with certainty whether the origin of T. infestans is Chacoan or Andean.

Occurrence of domestic and intrusive triatomines (Hemiptera: Reduviidae) in sylvatic habitats of the temperate Monte Desert ecoregion of Argentina

The eco-epidemiology of Triatominae and Trypanosoma cruzi transmission has been little studied in the Argentinean Monte ecoregion. Herein, we provide a comprehensive description of domestic and intrusive triatomines to evaluate the risk of reinfestation of rural dwellings. Triatoma infestans, T. patagonica, T. garciabesi and T. eratyrusiformis were collected by active searches or light traps. None were infected with T. cruzi. One T. infestans male was collected at 1.3 km from the nearest infested house. The finding of intrusive and domestic triatomines in sylvatic foci emphasizes the need of implementing an effective vector surveillance system.

Evolution, Systematics, and Biogeography of the Triatominae, Vectors of Chagas Disease

In this chapter, we review and update current knowledge about the evolution, systematics, and biogeography of the Triatominae (Hemiptera: Reduviidae)-true bugs that feed primarily on vertebrate blood. In the Americas, triatomines are the vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. Despite declining incidence and prevalence, Chagas disease is still a major public health concern in Latin America. Triatomines occur also in the Old World, where vector-borne T. cruzi transmission has not been recorded. Triatomines evolved from predatory reduviid bugs, most likely in the New World, and diversified extensively across the Americas (including the Caribbean) and in parts of Asia and Oceania. Here, we first discuss our current understanding of how, how many times, and when the blood-feeding habit might have evolved among the Reduviidae. Then we present a summary of recent advances in the systematics of this diverse group of insects, with an emphasis on the contribution of molecular tools to the clarification of taxonomic controversies. Finally, and in the light of both up-to-date phylogenetic hypotheses and a thorough review of distribution records, we propose a global synthesis of the biogeography of the Triatominae. Over 130 triatomine species contribute to maintaining T. cruzi transmission among mammals (sometimes including humans) in almost every terrestrial ecoregion of the Americas. This means that Chagas disease will never be eradicated and underscores the fact that effective disease prevention will perforce require stronger, long-term vector control-surveillance systems.

Beating the odds: Sustained Chagas disease vector control in remote indigenous communities of the Argentine Chaco over a seven-year period

BACKGROUND

Rapid reinfestation of insecticide-treated dwellings hamper the sustained elimination of Triatoma infestans, the main vector of Chagas disease in the Gran Chaco region. We conducted a seven-year longitudinal study including community-wide spraying with pyrethroid insecticides combined with periodic vector surveillance to investigate the house reinfestation process in connection with baseline pyrethroid resistance, housing quality and household mobility in a rural section of Pampa del Indio mainly inhabited by deprived indigenous people (Qom).

METHODOLOGY/PRINCIPAL FINDINGS

Despite evidence of moderate pyrethroid resistance in local T. infestans populations, house infestation dropped from 31.9% at baseline to 0.7% at 10 months post-spraying (MPS), with no triatomine found at 59 and 78 MPS. Household-based surveillance corroborated the rare occurrence of T. infestans and the house invasion of other four triatomine species. The annual rates of loss of initially occupied houses and of household mobility were high (4.6-8.0%). Housing improvements did not translate into a significant reduction of mud-walled houses and refuges for triatomines because most households kept the former dwelling or built new ones with mud walls.

CONCLUSIONS/SIGNIFICANCE

Our results refute the assumption that vector control actions performed in marginalized communities of the Gran Chaco are doomed to fail. The larger-than-expected impacts of the intervention program were likely associated with the combined effects of high-coverage, professional insecticide spraying followed by systematic vector surveillance-and-response, broad geographic coverage creating a buffer zone, frequent housing replacement and residential mobility. The dynamical interactions among housing quality, mobility and insecticide-based control largely affect the chances of vector elimination.

Wild populations of Triatoma infestans: Compilation of positive sites and comparison of their ecological niche with domestic population niche

BACKGROUND

For several years, the wild populations of Triatoma infestans, main vector of Trypanosoma cruzi causing Chagas disease, have been considered or suspected of being a source of reinfestation of villages. The number of sites reported for the presence of wild T. infestans, often close to human habitats, has greatly increased, but these data are scattered in several publications, and others obtained by our team in Bolivia have not been published yet.

METHODOLOGY/PRINCIPAL FINDINGS

Herein is compiled the largest number of wild sites explored for the presence of T. infestans collected with two methods The standardized methods aimed to determine the relationship between wild T. infestans and the ecoregion, and the directed method help to confirm the presence/absence of triatomines in the ecoregions. Entomological indices were compared between ecoregions and an environmental niche modelling approach, based on bioclimatic variables, was applied. The active search for wild T. infestans in Bolivia suggests a discontinuous distribution from the Andean valleys to the lowlands (Chaco), while the models used suggest a continuous distribution between the two regions and very large areas where wild populations remain to be discovered. The results compile the description of different habitats where these populations were found, and we demonstrate that the environmental niches of wild and domestic populations, defined by climatic variables, are similar but not equivalent, showing that during domestication, T. infestans has conquered new spaces with wider ranges of temperature and precipitation.

CONCLUSIONS/SIGNIFICANCE

The great diversity of wild T. infestans habitats and the comparison of their ecological niches with that of domestic populations confirm the behavioural plasticity of the species that increase the possibility of contact with humans. The result of the geographical distribution model of the wild populations calls for more entomological vigilance in the corresponding areas in the Southern Cone countries and in Bolivia. The current presentation is the most comprehensive inventory of wild T. infestans-positive sites that can be used as a reference for further entomological vigilance in inhabited areas.

Morphometric Wings Similarity among Sylvatic and Domestic Populations of Triatoma infestans (Hemiptera: Reduviidae) from the Gran Chaco Region of Paraguay

Despite sustained efforts for eliminating Triatoma infestans, reinfestation still persists in large part of the endemic area of Chagas disease from the Gran Chaco region. Sylvatic T. infestans populations seem to threat success of control programs of domestic T. infestans. In this study, we analyze whether T. infestans collected after a community-wide spraying were survivors or were immigrants from elsewhere using geometric morphometric tools. We used 101 right wings of female T. infestans captured before and after intervention program carried out in 12 de Junio and Casuarina, villages from Paraguayan Chaco, and in Puerto Casado during presprayed collection. There were no significant differences in wing size of domestic T. infestans between pre- and postspraying populations, and between domestic and sylvatic ones. When shape variables originating from postintervention individuals from 12 de Junio were introduced one by one into a discriminant analysis, the greatest weight (53%) was allocated to the sylvatic group. Furthermore, from the prespraying population, 25% were reallocated as postintervention individuals. Only 11% of the insects were reassigned to other groups Puerto Casado and Casuarina. These results suggest that postspraying individuals appear to have different origins. Half of the postspraying individuals from 12 de Junio were similar to the sylvatic ones and 25% of these were similar to those captured in the prespraying period. This remarkable morphometric wings similarity between sylvatic and domestic populations is new evidence suggesting that they could be highly related to each other in the Paraguayan Chaco; human-fed bugs from sylvatic area also support this.

Hosts and vectors of Trypanosoma cruzi discrete typing units in the Chagas disease endemic region of the Paraguayan Chaco

Active Trypanosoma cruzi transmission persists in the Gran Chaco region, which is considered hyperendemic for Chagas disease. Understanding domestic and sylvatic transmission cycles and therefore the relationship between vectors and mammalian hosts is crucial to designing and implementing improved effective control strategies. Here we describe the species of triatomine vectors and the sylvatic mammal reservoirs of T. cruzi, in different localities of the Paraguayan and Bolivian Chaco. We identify the T. cruzi genotypes discrete typing units (DTUs) and provide a map of their geographical distribution. A total of 1044 triatomines and 138 sylvatic mammals were captured. Five per cent of the triatomines were microscopically positive for T. cruzi (55 Triatoma infestans from Paraguay and one sylvatic Triatoma guasayana from Bolivia) and 17 animals (12·3%) comprising eight of 28 (28·5%) Dasypus novemcinctus, four of 27 (14·8%) Euphractus sexcinctus, three of 64 (4·7%) Chaetophractus spp. and two of 14 (14·3%) Didelphis albiventris. The most common DTU infecting domestic triatomine bugs was TcV (64%), followed by TcVI (28%), TcII (6·5%) and TcIII (1·5%). TcIII was overwhelmingly associated with armadillo species. We confirm the primary role of T. infestans in domestic transmission, armadillo species as the principal sylvatic hosts of TcIII, and consider the potential risk of TcIII as an agent of Chagas disease in the Chaco.

House Reinfestation With Triatoma infestans (Hemiptera: Reduviidae) After Community-Wide Spraying With Insecticides in the Argentine Chaco: A Multifactorial Process

We investigated the dynamics and underlying causes of house (re)infestation with Triatoma infestans (Klug 1834) after a community-wide residual spraying with pyrethroids in a well-defined rural section of Pampa del Indio municipality (northeastern Argentina) over a 4-yr period. House infestation was assessed by timed manual searches, during insecticide applications, and by opportunistic householders' bug collections. All reinfested houses were selectively re-sprayed with insecticides. The resident population comprised Qom (66.6%) and Creole (33.4%) households, whose sociodemographic profiles differed substantially. The prevalence of house infestation dropped, less than expected, from 20.5% at baseline to 5.0% at 14 months postspraying (MPS), and then fluctuated between 0.8 and 4.2% over 21-51 MPS. Postspraying house infestation was positively and highly significantly associated with prespraying infestation. Most of the foci detected over 14-21 MPS were considered persistent (residual), some of which were moderately resistant to pyrethroids and were suppressed with malathion. Infestation patterns over 27-51 MPS suggested bug invasion from internal or external foci, but the sources of most findings were unaccounted for. Local spatial analysis identified two hotspots of postspraying house infestation. Using multimodel inference with model averaging, we corroborated that baseline domestic infestation was closely related to refuge availability, housing quality, and occurrence of peridomestic infestation. The diminished effectiveness of single pyrethroid treatments, partly attributable to moderate resistance compounded with rather insensitive vector detection methods and poor housing conditions, contributed to vector persistence. Improved control strategies combined with broad social participation are needed for the sustainable elimination of vector-borne human Chagas disease from the Gran Chaco.

Genetic characterization of residual Triatoma infestans populations from Brazil by microsatellite

In spite of long-term efforts to eliminate Triatoma infestans (Klug 1834) from Brazil, residual foci still persist in the states of Bahia and Rio Grande do Sul. Data on the genetic variability and structuring of these populations are however lacking. Using nine microsatellite loci, we characterized one residual T. infestans population from Bahia and four from Rio Grande do Sul, and compared them with bugs originally from an older focus in São Paulo; 224 bugs were genotyped. The number of alleles per locus ranged from 5 to 11. Observed and expected heterozygosities per locus ranged, respectively, from 0 to 0.786 and from 0 to 0.764. Significant departures from Hardy-Weinberg equilibrium, mainly due to heterozygote deficits, were detected in all loci and in most populations. Global indices estimated by AMOVA were: Fis was 0.37; Fst was 0.28; and Fit was 0.55; overall indices with p = 0.00 indicated substantial differentiation. Inter-population Fst ranged from 0.118 to 0.562, suggesting strong genetic structuring and little to no gene flow among populations. Intra-population Fis ranged from 0.301 to 0.307. Inbreeding was apparent in all populations except that from Bahia-which might be either linked by gene flow to nearby unsampled populations or part of a relatively large local population. The overall pattern of strong genetic structuring among pyrethroid-susceptible residual T. infestans populations suggests that their persistence is probably due to operational control failures. Detection and elimination of such residual foci is technically feasible and must become a public health priority in Brazil.

A motorized vehicle-mounted sprayer as a new tool for Chagas disease vector control

Abstract: Residual insecticide spraying still is the main tool used to suppress house infestations with Chagas disease vectors. While manual compression sprayers (MCS) have traditionally been used in Latin America, Mendoza's vector control program from Argentina introduced the use of a modified motorized vehicle-mounted sprayer (VMS) with apparent advantages over MCS. We conducted a randomized intervention trial to evaluate the effectiveness and selected components of the performance of MCS and VMS. We assessed house infestation by Triatoma infestans in 76 previously-infested houses at 0, 1, 4 and 12 months postintervention. Infestations were reduced substantially, with no significant differences between treatments. End-point infestations were restricted to peridomiciles. Although VMS required less time to complete the house spraying than MCS, both treatments had similar performance and did not suppress infestations completely. The main relative advantages of VMS were a reduced physical effort, especially under harsh field conditions, and potential gains in spray coverage per unit of time.

The Evolutionary Origin of Diversity in Chagas Disease Vectors

Chagas disease is amongst the ten most important neglected tropical diseases but knowledge on the diversification of its vectors, Triatominae (Hemiptera: Reduviidae), is very scarce. Most Triatominae species occur in the Americas, and are all considered potential vectors. Despite its amazing ecological vignette, there are remarkably few evolutionary studies of the whole subfamily, and only one genome sequence has been published. The young age of the subfamily, coupled with the high number of independent lineages, are intriguing, yet the lack of genome-wide data makes it a challenge to infer the phylogenetic relationships within Triatominae. Here we synthesize what is known, and suggest the next steps towards a better understanding of how this important group of disease vectors came to be.

First finding of Trypanosoma cruzi II in vampire bats from a district free of domestic vector-borne transmission in Northeastern Argentina

Establishing the putative links between sylvatic and domestic transmission cycles of Trypanosoma cruzi, the etiological agent of Chagas disease, is of public health relevance. We conducted three surveys to assess T. cruzi infection in wild mammals from a rural and a preserved area in Misiones Province, Northeastern Argentina, which had recently been declared free of vector- and blood-borne transmission of human T. cruzi infection. A total of 200 wild mammals were examined by xenodiagnosis (XD) and/or polymerase chain reaction (PCR) amplification of the hyper-variable region of kinetoplast DNA minicircles of T. cruzi (kDNA-PCR). The overall prevalence of T. cruzi infection was 8%. Nine (16%) of 57 Didelphis albiventris opossums and two (7%) of 29 Desmodus rotundus vampire bats were positive by both XD and kDNA-PCR. Additionally, one D. rotundus positive for T. cruzi by kDNA-PCR tested positive by satellite-DNA-PCR (SAT-DNA-PCR). The T. cruzi-infected bats were captured indoors and in the yard of a vacant dwelling. All D. albiventris were infected with TcI and both XD-positive D. rotundus by TcII. Fifty-five opossum cubs within the marsupium were negative by XD. The mean infectiousness to the vector was 62% in D. albiventris and 50% in D. rotundus. Mice experimentally infected with a parasite isolate from a vampire bat displayed lesions typically caused by T. cruzi. Our study documents the presence of the genotype TcII in a sylvatic host for the first time in Argentina, and the occurrence of two transmission cycles of T. cruzi in a district free of domestic vector-borne transmission.

Intrusive versus domiciliated triatomines and the challenge of adapting vector control practices against Chagas disease

Chagas disease prevention remains mostly based on triatomine vector control to reduce or eliminate house infestation with these bugs. The level of adaptation of triatomines to human housing is a key part of vector competence and needs to be precisely evaluated to allow for the design of effective vector control strategies. In this review, we examine how the domiciliation/intrusion level of different triatomine species/populations has been defined and measured and discuss how these concepts may be improved for a better understanding of their ecology and evolution, as well as for the design of more effective control strategies against a large variety of triatomine species. We suggest that a major limitation of current criteria for classifying triatomines into sylvatic, intrusive, domiciliary and domestic species is that these are essentially qualitative and do not rely on quantitative variables measuring population sustainability and fitness in their different habitats. However, such assessments may be derived from further analysis and modelling of field data. Such approaches can shed new light on the domiciliation process of triatomines and may represent a key tool for decision-making and the design of vector control interventions.

Susceptibility to deltamethrin of wild and domestic populations of Triatoma infestans of the Gran Chaco and the Inter-Andean Valleys of Bolivia

Background

The persistence of Triatoma infestans and the continuous transmission of Trypanosoma cruzi in the Inter-Andean Valleys and in the Gran Chaco of Bolivia are of great significance. Coincidentally, it is in these regions the reach of the vector control strategies is limited, and reports of T. infestans resistance to insecticides, including in wild populations, have been issued. This study aims to characterize the susceptibility to deltamethrin of wild and domestic populations of T. infestans from Bolivia, in order to better understand the extent of this relevant problem.

Methods

Susceptibility to deltamethrin was assessed in nine, wild and domestic, populations of T. infestans from the Gran Chaco and the Inter-Andean Valleys of Bolivia. Serial dilutions of deltamethrin in acetone (0.2 μL) were topically applied in first instar nymphs (F1, five days old, fasting, weight 1.2 ± 0.2 mg). Dose response results were analyzed with PROBIT version 2, determining the lethal doses, slope and resistance ratios (RR). Qualitative tests were also performed.

Results

Three wild T. infestans dark morph samples of Chaco from the Santa Cruz Department were susceptible to deltamethrin with RR₅₀ of <2, and 100% mortality to the diagnostic dose (DD); however, two domestic populations from the same region were less susceptible than the susceptibility reference lineage (RR₅₀ of 4.21 and 5.04 respectively and 93% DD). The domestic population of Villa Montes from the Chaco of the Tarija Department presented high levels of resistance (RR₅₀ of 129.12 and 0% DD). Moreover, the domestic populations from the Valleys of the Cochabamba Department presented resistance (RR₅₀ of 8.49 and 62% DD), the wild populations were less susceptible than SRL and T. infestans dark morph populations (RR₅₀ < 5).

Conclusion

The elimination of T. infestans with pyrethroid insecticides in Brazil, Uruguay, Chile, and its drastic reduction in large parts of Paraguay and Argentina, clearly indicates that pyrethroid resistance was very uncommon in non-Andean regions. The pyrethroid susceptibility of non-Andean T. infestans dark morph population, and the resistance towards it, of Andean T. infestans wild and domestic populations, indicates that the Andean populations from Bolivia are less susceptible.

Toxicological and biochemical analysis of the susceptibility of sylvatic Triatoma infestans from the Andean Valley of Bolivia to organophosphate insecticide

To increase our knowledge of the natural susceptibility of Triatoma infestans to an organophosphate insecticide, we performed toxicological and biochemical studies on three sylvatic populations from Bolivia and two populations from domestic dwellings from Bolivia and Argentina. Fifty-per-cent lethal doses (LD50) were determined based on the topical application of fenitrothion on first instar nymphs and mortality was assessed at 24 h. Both type of populations exhibited LD50ratios significantly higher than 1 with a range of the values (1.42-2.47); the maximum value were found in a sylvatic (-S) population, Veinte de Octubre-S. Samples were biochemically analysed using a glutathione S-transferase activity assay. The highest significant activity was obtained for Veinte de Octubre-S and the lowest activity was obtained for the reference population (102.69 and 54.23 pmol per minute per mg of protein respectively). Two out of the three sylvatic populations (Veinte de Octubre-S and Kirus Mayu-S) exhibited significantly higher glutathione S-transferase activity than that of the reference population. Based on this analysis of the natural susceptibility of this organism to organophosphate insecticides, continental and focal surveys of organophosphate susceptibility should be conducted to evaluate the evolution and distribution of this phenomenon.

Evolutionary and dispersal history of Triatoma infestans, main vector of Chagas disease, by chromosomal markers

Chagas disease, one of the most important vector-borne diseases in the Americas, is caused by Trypanosoma cruzi and transmitted to humans by insects of the subfamily Triatominae. An effective control of this disease depends on elimination of vectors through spraying with insecticides. Genetic research can help insect control programs by identifying and characterizing vector populations. In southern Latin America, Triatoma infestans is the main vector and presents two distinct lineages, known as Andean and non-Andean chromosomal groups, that are highly differentiated by the amount of heterochromatin and genome size. Analyses with nuclear and mitochondrial sequences are not conclusive about resolving the origin and spread of T. infestans. The present paper includes the analyses of karyotypes, heterochromatin distribution and chromosomal mapping of the major ribosomal cluster (45S rDNA) to specimens throughout the distribution range of this species, including pyrethroid-resistant populations. A total of 417 specimens from seven different countries were analyzed. We show an unusual wide rDNA variability related to number and chromosomal position of the ribosomal genes, never before reported in species with holocentric chromosomes. Considering the chromosomal groups previously described, the ribosomal patterns are associated with a particular geographic distribution. Our results reveal that the differentiation process between both T. infestans chromosomal groups has involved significant genomic reorganization of essential coding sequences, besides the changes in heterochromatin and genomic size previously reported. The chromosomal markers also allowed us to detect the existence of a hybrid zone occupied by individuals derived from crosses between both chromosomal groups. Our genetic studies support the hypothesis of an Andean origin for T. infestans, and suggest that pyrethroid-resistant populations from the Argentinean-Bolivian border are most likely the result of recent secondary contact between both lineages. We suggest that vector control programs should make a greater effort in the entomological surveillance of those regions with both chromosomal groups to avoid rapid emergence of resistant individuals.

Triatominae in furnariid nests of the Argentine Gran Chaco

Triatomines (Hemiptera, Reduviidae) are bloodsucking insects involved in the transmission of Trypanosoma cruzi, the causative agent of Chagas disease, an important public health problem in Latin America. The triatomine species found in sylvatic habitats generally play a limited epidemiological role compared to domestic species, but they may act as a reinfestation source of dwellings after insecticide spraying and have to be carefully considered in control strategies of Chagas disease transmission. The objectives of this work were to carry out a survey of the sylvatic triatomine species colonizing Furnariidae nests in a typical area of the Chaco region of Argentina during the winter and to study the parasites and natural enemies associated with the collected triatomines. Sixty-three triatomine specimens were collected from Furnariidae nests (Coryphistera alaudina and Phacellodomus sibilatrix) randomly selected within the study area. Fifty-four were identified as Psammolestes coreodes, seven as Triatoma platensis, and two as Triatoma infestans. Specimens of T. infestans and T. platensis were found in one nest. The first finding of instar nymphs of T. infestans x T. platensis in a sylvatic habitat is reported. For the first time, sylvatic collected specimens of T. platensis were found infected by T. cruzi. Triatoma virus was found in one Ps. coreodes specimen.

Variations in time and space of an Andean wild population of T. infestans at a microgeographic scale

Background

Wild populations of Triatoma infestans are now believed to be the source of reinfestation of dwellings in some Andean areas and could impede the full achievement of vector control campaigns in this region. Given the poor knowledge of these populations in natural conditions, their basic biology traits, such as monthly demographic variations and movements of individuals, were explored.

Methods

A previously identified wild population of T. infestans in a field adjacent to a group of isolated houses in an Andean valley (department of La Paz, Bolivia) was explored using regular capture assays over 13 months in 50 sites selected at the beginning of the study. The capture-mark-recapture method was applied monthly using mouse-baited adhesive traps for captures and fingernail polish of different colors for the marking.

Results

The monthly capture assays did not show significant differences between rainy and dry seasons, showing evidence for a certain stability of the wild T. infestans population with only the nymph population tending to decline during the middle of the rainy season when rain is more intensive. Throughout the study, the monthly average number of bugs was 51.1 ± 25.3 per assay, 91.1% were nymphs, and they were found at 30 of the 50 sites (60%). The number of times a site was positive varied from one to 13. Site infestation was associated with the underground position of the traps, and rocks around and in the surroundings of the traps. The recaptures after marking were successful (138 recaptures over the study). The marking made it possible to detect for 14.5% of the recaptures significant movements of adults (up to 168 m) and nymphs (up to 34 m). Some bugs (nymphs and females) were recaptured after 5 months. For adults, recaptures (46 in total) mostly occurred between September and March. Females were recaptured twice as frequently as males.

Conclusion

The Andean wild populations of T. infestans showed a strong spatial and temporal stability during the year-long study. Dispersal may occur mainly during the rainy season. The capture-mark-recapture method was successful and the longevity of the bugs and the distances covered by nymphs and adults were recorded.

A multi-species bait for Chagas disease vectors

Background

Triatomine bugs are the insect vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. These insects are known to aggregate inside shelters during daylight hours and it has been demonstrated that within shelters, the aggregation is induced by volatiles emitted from bug feces. These signals promote inter-species aggregation among most species studied, but the chemical composition is unknown.

Methodology/Principal Findings

In the present work, feces from larvae of the three species were obtained and volatile compounds were identified by solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). We identified five compounds, all present in feces of all of the three species: Triatoma infestans, Panstrongylus megistus and Triatoma brasiliensis. These substances were tested for attractivity and ability to recruit insects into shelters. Behaviorally active doses of the five substances were obtained for all three triatomine species. The bugs were significantly attracted to shelters baited with blends of 160 ng or 1.6 µg of each substance.

Conclusions/Significance

Common compounds were found in the feces of vectors of Chagas disease that actively recruited insects into shelters, which suggests that this blend of compounds could be used for the development of baits for early detection of reinfestation with triatomine bugs.

Chagas disease is a parasitic infection affecting approximately 12 million people, and is considered to be one of the most severe burdens for public health in Latin America. Control of the disease is based on attempted elimination of domestic populations of triatomine bugs, the insects transmitting the disease to humans, by means of insecticide spraying. Currently, vigilance programs monitoring triatomine reinfestation processes in houses are performed by manual search for bugs. Effective and sustainable new methods allowing continuous monitoring of domestic triatomine populations are required. Based on the fact that the insects hide in dark refuges that are marked by volatile signals emitted in their feces, we screened the feces of three species for volatile compounds common to these prominent vectors. The potential for these odors to promote triatomine aggregation was evaluated and we present evidence that a synthetic blend of these substances is capable of recruiting bugs into shelters, mimicking the natural pheromone. This blend may be used to develop a bait to monitor triatomine reinfestation processes in a similar manner as is used commonly for the monitoring of agricultural pests.

Wild populations of Triatoma infestans are highly connected to intra-peridomestic conspecific populations in the Bolivian Andes

Triatoma infestans, the major vector of Chagas disease south of the Amazon in South America, has a large distribution of wild populations, contrary to what has previously been stated. These populations have been suspected of being the source of reinfestation of human habitats and could impede the full success of vector control campaigns. This study examined gene flow between intra-peridomestic populations and wild populations collected in the surround areas in three Andean localities in Bolivia. The populations were defined according to temporal, ecological, and spatial criteria. After DNA extraction from the legs of each insect, the samples were analyzed using seven microsatellite markers. First, the analysis of molecular variance (AMOVA) detected an absence of differentiation between wild and intra-peridomestic populations, although strong structuring was observed between the populations within each environment. Then for some populations, the Bayesian method of assignment to inferred populations showed very similar assignment patterns of the members of wild or intra-peridomestic populations in each locality. Finally, the detection of the first-generation migrants within the different populations provided evidence of insect displacement from the wild to the intra-peridomestic environment. This result indicates that, after control campaigns in the Andes, controlling this new paradigm of vector transmission risk stemming from the invasion of human habitats by wild populations of T. infestans requires long-term maintenance of public monitoring to keep the risk at a minimal level. Since wild populations of T. infestans have also been detected elsewhere in Argentina, Paraguay, and Chile, there is an urgent need to take these populations into account in future monitoring of Chagas disease transmission.

Susceptibility and resistance to deltamethrin of wild and domestic populations of Triatoma infestans (Reduviidae: Triatominae) in Bolivia: new discoveries

Bolivia is a high-endemic country for Chagas disease, for which the principal vector is Triatoma infestans (Triatominae). This is a mainly domestic species that is also found in the wild environment. Recently, an increasing number of studies have shown the importance of Triatominae resistance to insecticides, especially in Bolivia. Data regarding the susceptibility/resistance of wild and domestic populations of T. infestans to deltamethrin are presented. For the first time, domestic populations of the department of Santa Cruz were tested, showing low resistance. Although most of the wild populations were found to be susceptible to deltamethrin, three populations from three departments showed a mortality rate of less than 100%. This result is emphasised here.

Origins of house reinfestation with Triatoma infestans after insecticide spraying in the Argentine Chaco using wing geometric morphometry

Identifying the origins of insect vectors collected after community-wide residual insecticide applications is a relevant challenge in the Gran Chaco region where the main vector of Chagas disease Triatoma infestans usually reinfests human dwellings. Wing geometric morphometry was used to compare the right wings of 63 males and 54 females collected at 4 months post-spraying (MPS) with those from 165 males and 111 females collected before full-coverage spraying with pyrethroids in a well-defined rural area in Northeastern Argentina. Male and female wing centroid size resulted significantly larger at 4MPS than before interventions, but no significant changes in shape were detected. Metric disparity (variance of shape) varied significantly in males but not in females. Using shape variables, a relatively large fraction of post-spraying males (70%) and females (54%) could not be differentiated from those collected at the same source house or at the nearest infested house before interventions. Bugs collected at 4 and 8MPS in a persistently infested house were mainly assigned to the source house. These results support the hypothesis of persistent bug populations that survived the insecticide application at local spatial scales, and are consistent with the occurrence of vector control failures most likely related to moderate pyrethroid resistance. Wing geometric morphometry is a useful tool for identifying sources of reinfestation, but it is limited by the spatial structure found in the reference populations. Combined with field and genetic data, this approach may contribute to the understanding of the reinfestation process and improvement of vector control strategies.

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.

The sylvatic transmission cycle of Trypanosoma cruzi in a rural area in the humid Chaco of Argentina

Little is known about the sylvatic transmission cycle of Trypanosoma cruzi in the Gran Chaco ecoregion. We conducted surveys to identify the main sylvatic hosts of T. cruzi, parasite discrete typing units and vector species involved in Pampa del Indio, a rural area in the humid Argentinean Chaco. A total of 44 mammals from 14 species were captured and examined for infection by xenodiagnosis and polymerase chain reaction amplification of the hyper-variable region of kinetoplast DNA minicircles of T. cruzi (kDNA-PCR). Ten (22.7%) mammals were positive by xenodiagnosis or kDNA-PCR. Four of 11 (36%) Didelphis albiventris (white-eared opossums) and six of nine (67%) Dasypus novemcinctus (nine-banded armadillos) were positive by xenodiagnosis and or kDNA-PCR. Rodents, other armadillo species, felids, crab-eating raccoons, hares and rabbits were not infected. Positive animals were highly infectious to the bugs that fed upon them as determined by xenodiagnosis. All positive opossums were infected with T. cruzi I and all positive nine-banded armadillos with T. cruzi III. Extensive searches in sylvatic habitats using 718 Noireau trap-nights only yielded Triatoma sordida whereas no bug was collected in 26 light-trap nights. Four armadillos or opossums fitted with a spool-and-line device were successfully tracked to their refuges; only one Panstrongylus geniculatus was found in an armadillo burrow. No sylvatic triatomine was infected with T. cruzi by microscopical examination or kDNA-PCR. Our results indicate that two independent sylvatic transmission cycles of T. cruzi occur in the humid Chaco. The putative vectors of both cycles need to be identified conclusively.

Ecological connectivity of Trypanosoma cruzi reservoirs and Triatoma pallidipennis hosts in an anthropogenic landscape with endemic Chagas disease

Traditional methods for Chagas disease prevention are targeted at domestic vector reduction, as well as control of transfusion and maternal-fetal transmission. Population connectivity of Trypanosoma cruzi-infected vectors and hosts, among sylvatic, ecotone and domestic habitats could jeopardize targeted efforts to reduce human exposure. This connectivity was evaluated in a Mexican community with reports of high vector infestation, human infection, and Chagas disease, surrounded by agricultural and natural areas. We surveyed bats, rodents, and triatomines in dry and rainy seasons in three adjacent habitats (domestic, ecotone, sylvatic), and measured T. cruzi prevalence, and host feeding sources of triatomines. Of 12 bat and 7 rodent species, no bat tested positive for T. cruzi, but all rodent species tested positive in at least one season or habitat. Highest T. cruzi infection prevalence was found in the rodents, Baiomys musculus and Neotoma mexicana. In general, parasite prevalence was not related to habitat or season, although the sylvatic habitat had higher infection prevalence than by chance, during the dry season. Wild and domestic mammals were identified as bloodmeals of T. pallidipennis, with 9% of individuals having mixed human (4.8% single human) and other mammal species in bloodmeals, especially in the dry season; these vectors tested >50% positive for T. cruzi. Overall, ecological connectivity is broad across this matrix, based on high rodent community similarity, vector and T. cruzi presence. Cost-effective T. cruzi, vector control strategies and Chagas disease transmission prevention will need to consider continuous potential for parasite movement over the entire landscape. This study provides clear evidence that these strategies will need to include reservoir/host species in at least ecotones, in addition to domestic habitats.

Differential pattern of infection of sylvatic nymphs and domiciliary adults of Triatoma infestans with Trypanosoma cruzi genotypes in Chile

In Chile, the main vector of Chagas disease, Triatoma infestans, is under control after insecticide spraying. However, it has been found colonizing wild habitats. This study evaluated Trypanosoma cruzi infection of sylvatic and domiciliary T. infestans and identified their parasite genotypes. The sample studied was composed mainly of T. infestans sylvatic nymphs and domiciliary adults from a semi-urban area with human dwellings under vector control surveillance. Results showed prevalences of 57.7% in nymphs and 68.6% in adults. Hybridization tests showed a major T. cruzi lineage (TcI) circulating in sylvatic (93.3%) and domiciliary (100%) T. infestans. TcII, TcV, and TcVI were also detected, mainly in nymphs, suggesting differential adaptation of T. cruzi lineages among instars. We also discuss the origin of domiciliary individuals of T. infestans and the risk of human infection by triatomines of sylvatic foci that invade houses despite vector control programs.

Lack of segregation between two species of Chagas disease vectors

Triatoma infestans and Panstrongylus megistus are relevant Chagas disease vectors. An apparent segregation among these triatomine species inside human households was suggested to rely on mutual repellence between them. However, P. megistus and T. infestans show aggregation responses to chemical signals emitted by the other species. These findings do not rule out the possibility that stimuli other than chemical signals could mediate repellence when these species exploit shelters simultaneously. In the present study, we investigated how P. megistus and T. infestans exploit shelters in controlled laboratory conditions and how insect density and environmental illumination modulate this behavior. We evaluated whether these species aggregate inside shelters or mutually repel each other. Panstrongylus megistus and T. infestans show specific patterns of shelter exploitation, which are differentially affected by insect density and environment illumination. In particular, P. megistus is more sensitive to insect density than T. infestans, whereas T. infestans shows higher sensitivity to illumination than P. megistus. Nevertheless, these species exploit shelters randomly without any apparent repellence.

Genetic characterization of Trypanosoma cruzi DTUs in wild Triatoma infestans from Bolivia: predominance of TcI

Background

The current persistence of Triatoma infestans (one of the main vectors of Chagas disease) in some domestic areas could be related to re-colonization by wild populations which are increasingly reported. However, the infection rate and the genetic characterization of the Trypanosoma cruzi strains infecting these populations are very limited.

Methodology/Principal Findings

Of 333 wild Triatoma infestans specimens collected from north to south of a Chagas disease endemic area in Bolivia, we characterized 234 stocks of Trypanosoma cruzi using mini-exon multiplex PCR (MMPCR) and sequencing the glucose phosphate isomerase (Gpi) gene. Of the six genetic lineages (“discrete typing units”; DTU) (TcI-VI) presently recognized in T. cruzi, TcI (99.1%) was overdominant on TcIII (0.9%) in wild Andean T. infestans, which presented a 71.7% infection rate as evaluated by microscopy. In the lowlands (Bolivian Chaco), 17 “dark morph” T. infestans were analyzed. None of them were positive for parasites after microscopic examination, although one TcI stock and one TcII stock were identified using MMPCR and sequencing.

Conclusions/Significance

By exploring large-scale DTUs that infect the wild populations of T. infestans, this study opens the discussion on the origin of TcI and TcV DTUs that are predominant in domestic Bolivian cycles.

Chagas disease is a neglected parasitic disease transmitted by bugs (vectors) and represents a serious health problem in the Americas. Although the transmission generally occurs in the houses where the bugs are living, wild populations of vectors are now considered a problem because these populations might enter the houses and recolonize them after eliminating of house populations by insecticide spraying. This is the case of the Southern countries where Triatoma infestans, the principal vector, transmits Trypanosoma cruzi the agent of the disease. This parasite presents a large genetic variability and it is important to know which T. cruzi genotypes are carried by the vectors. The authors found that in the wild T. infestans from the Bolivian Andean region, a principal group of genotype was circulating. In the lowlands (Bolivian Chaco), another additional genotype group was detected. Together with exploring at large scale which genotypes are infecting T. infestans wild populations, this study opens the discussion on the origin T. cruzi genotype groups. Also this study completes our basic knowledge on T. cruzi subspecific genetic variability, and therefore brings new tools for molecular epidemiology of Chagas disease.

New discoveries of sylvatic Triatoma infestans (Hemiptera: Reduviidae) throughout the Bolivian Chaco

Sylvatic populations of Triatoma infestans might be involved in the recolonization of human dwellings. We report here the discoveries of new T. infestans sylvatic foci in the Bolivian Chaco. Eighty-one triatomines were caught, 38 of which were identified as T. infestans. Triatoma sordida and Panstrongylus geniculatus were the other species collected. One T. infestans and one T. sordida were infected with Trypanosoma cruzi TcI; one T. infestans was infected with TcII. These discoveries add to the debate on the geographic distribution of sylvatic T. infestans populations, the geographic origin of the species, and the epidemiological role of these populations.

Factors affecting infestation by Triatoma infestans in a rural area of the humid Chaco in Argentina: a multi-model inference approach

Background

Transmission of Trypanosoma cruzi by Triatoma infestans remains a major public health problem in the Gran Chaco ecoregion, where understanding of the determinants of house infestation is limited. We conducted a cross-sectional study to model factors affecting bug presence and abundance at sites within house compounds in a well-defined rural area in the humid Argentine Chaco.

Methodology/Principal Findings

Triatoma infestans bugs were found in 45.9% of 327 inhabited house compounds but only in 7.4% of the 2,584 sites inspected systematically on these compounds, even though the last insecticide spraying campaign was conducted 12 years before. Infested sites were significantly aggregated at distances of 0.8–2.5 km. The most frequently infested ecotopes were domiciles, kitchens, storerooms, chicken coops and nests; corrals were rarely infested. Domiciles with mud walls and roofs of thatch or corrugated tarred cardboard were more often infested (32.2%) than domiciles with brick-and-cement walls and corrugated metal-sheet roofs (15.1%). A multi-model inference approach using Akaike's information criterion was applied to assess the relative importance of each variable by running all possible (17,406) models resulting from all combinations of variables. Availability of refuges for bugs, construction with tarred cardboard, and host abundance (humans, dogs, cats, and poultry) per site were positively associated with infestation and abundance, whereas reported insecticide use showed a negative association. Ethnic background (Creole or Toba) adjusted for other factors showed little or no association.

Conclusions/Significance

Promotion and effective implementation of housing improvement (including key peridomestic structures) combined with appropriate insecticide use and host management practices are needed to eliminate infestations. Fewer refuges are likely to result in fewer residual foci after insecticide spraying, and will facilitate community-based vector surveillance. A more integrated perspective that considers simultaneously social, economic and biological processes at local and regional scales is needed to attain effective, sustainable vector and disease control.

Vector-borne transmission of Chagas disease remains a major public health problem in parts of Latin America. Triatoma infestans is the main vector in the countries located in the South American Cone, particularly in the Gran Chaco ecoregion where residual insecticide control has achieved only a moderate, irregular impact. To contribute to improved control strategies, we analyzed the factors associated with the presence and abundance of T. infestans in 327 inhabited houses in a well-defined rural area with no recent vector control interventions in the humid Argentine Chaco. Bugs were found mainly in domiciles, kitchens, storerooms, and chicken coops and nests, particularly where adequate refuge and animal hosts (humans, dogs, cats or poultry) were available. Domiciles constructed from mud were the most often infested, but brick-and-cement domiciles, even in good conditions, were also found infested. Availability of refuge and hosts for T. infestans are key targets for vector control. Ten-fold variations in domestic infestation observed across neighboring villages, and differences in the relevant factors for T. infestans presence with respect to other areas of the Gran Chaco region suggest that host management, building techniques and insecticide use need to be tailored to the local environment, socio-economic characteristics, and climatic conditions.

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

BACKGROUND

Establishing 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 FINDINGS

During 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.

CONCLUSIONS

Our 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.

Genetic variability, phylogenetic relationships and gene flow in Triatoma infestans dark morphs from the Argentinean Chaco

The recent discovery of sylvatic populations of Triatoma infestans outside the Andean Valleys of Bolivia prompted an evolutionary question about the putative ancestral area of origin and dispersal of the species, and an epidemiological question regarding the possible role of these sylvatic populations in the recolonization process of insecticide-treated houses. The finding of a population of sylvatic melanic T. infestans (dark morphs) in the Argentinean dry Chaco at 7 km from a peridomestic bug population of typical coloration gave us the opportunity to test both questions simultaneously by employing phylogenetic and population genetic approaches. For this purpose we analyzed sylvatic and peridomestic bugs using sequence-based mitochondrial and nuclear markers (mtCOI and ITS-1) and microsatellites. Sylvatic bugs were confirmed to be T. infestans and not hybrids, and showed high levels of genetic variability and departures from neutral expectations for mtCOI variation. New ITS-1 and mtCOI haplotypes were recorded, as well as haplotypes shared with peridomestic and/or domestic bugs from previous records. The peridomestic population was invariant for ITS-1 and mtCOI, but showed variability for microsatellites and signatures of a population bottleneck, probably due to a limited number of founders. Phylogenetic analyses were consistent with the presence of ancestral haplotypes in sylvatic bugs. According to F-statistics and assignment methods there was a significant differentiation between sylvatic and peridomestic bugs and gene flow was low and asymmetric, with more bugs moving from the peridomicile to the sylvatic environment. These results support the hypothesis of the Chaco region as the area of origin of T. infestans, and a limited role of sylvatic melanic T. infestans in peridomestic infestation in the Argentinean Chaco.

Susceptibility of sylvatic Triatoma infestans from Andeans valleys of Bolivia to deltamethrin and fipronil

We describe the susceptibility to deltamethrin and fipronil of four sylvatic Triatoma infestans populations from the Andean valleys of Bolivia. Fifty percent lethal doses were determined from topical application of insecticide on first instars, and mortality was assessed after 24 h for deltamethrin and 48 h for fipronil. In comparison with a reference strain from Argentina, the Bolivian populations showed deltamethrin 50 percent lethal dose ratios ranging from 1.9 to 17.4. In the case of fipronil, an insecticide never used for control of T. infestans, the Bolivian populations showed even higher variation in toxic response, with relative susceptibilities ranging from 0.5 to 139.2. However, although the sylvatic T infestans toxicological profiles differ from each other and from those of the domiciliary population studied in this work, there were no significant differences in the activities of P450 mono-oxygenases and pyrethroid esterases between the reference strain and the studied populations.

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.

New insights on the Chagas disease main vector Triatoma infestans (Reduviidae, Triatominae) brought by the genetic analysis of Bolivian sylvatic populations

Triatoma infestans is the main and most widespread vector of Chagas disease in South America. For the first time, a large sample of sylvatic populations of T. infestans was analyzed by ITS-2 and mtCytB sequencing. ITS-2 showed a low level of polymorphism but revealed a dichotomy between the Andean and non-Andean sylvatic populations. On the contrary, mtCytB sequences showed a high polymorphism (19 haplotypes determined by 35 variable sites) revealing a strong structuring between most of the sylvatic populations and possible ancient isolation and bottleneck in the Northern Andes. The dichotomy Andean vs. non-Andean populations was not observed with this marker. Moreover, mtCytB haplotype genealogies showed that the non-Andean haplotypes would have derived from the Andean ones, supporting somewhat an Andean origin of the species. Nevertheless, a non-Andean origin could not be discarded because a remarkable genetic diversity was found in the non-Andean sample. The comparison of the sylvatic haplotypes with the domestic ones from GenBank suggested multiple events of T. infestans domestication in Andean and non-Andean areas, instead of a major and unique domestication event in the Bolivian Andes, as previously proposed.

New insights on the spread of Triatoma infestans from Bolivia--implications for Chagas disease emergence in the southern cone

Triatoma infestans, now eliminated from most of South America by control campaigns, has been and still is the main Chagas disease vector due to its ability to colonize rural dwellings. The traditional hypothesis put forth to explain T. infestans adaptation to the synanthropic environment rests on the domestication of wild guinea pigs, one of its natural hosts, by Andean tribes about 5000 BC. Here we present two new hypotheses, based on organized human social activities. The first involves maize production, storage and distribution during the Inca period. Maize granaries could host wild rodent populations that would attract sylvatic T. infestans that were later dispersed during maize distribution. The second hypothesis is associated with the contemporary Urkupiña Virgin festival, near Cochabamba, where thousands of pilgrims gather for rituals in an area that is part of a sylvatic T. infestans focus, thus favoring the contact with the insects and leading to their passive dispersal.