Trypanosoma cruzi infection in Triatoma sordida before and after community-wide residual insecticide spraying in the Argentinean Chaco

The Pampa del Indio project: sustainable vector control and long-term declines in the prevalence and abundance of Triatoma infestans infected with Trypanosoma cruzi in the Argentine Chaco

BACKGROUND

The Gran Chaco region is a major hotspot of Chagas disease. We implemented a 9-year program aimed at suppressing house infestation with Triatoma infestans and stopping vector-borne transmission to creole and indigenous (Qom) residents across Pampa del Indio municipality (Argentine Chaco). The aim of the present study was to assess the intervention effects on parasite-based transmission indices and the spatial distribution of the parasite, and test whether house-level variations in triatomine infection with Trypanosoma cruzi declined postintervention and were influenced by household ethnicity, persistent infestation linked to pyrethroid resistance and other determinants of bug infection.

METHODS

This longitudinal study assessed house infestation and bug infection with T. cruzi before and after spraying houses with pyrethroids and implemented systematic surveillance-and-response measures across four operational areas over the period 2007-2016. Live triatomines were individually examined for infection by optical microscopy or kinetoplast DNA (kDNA)-PCR and declared to be infected with T. cruzi when assessed positive by either method.

RESULTS

The prevalence of infection with T. cruzi was 19.4% among 6397 T. infestans examined. Infection ranged widely among the study areas (12.5-26.0%), household ethnicity (15.3-26.9%), bug ecotopes (1.8-27.2%) and developmental stages (5.9-27.6%), and decreased from 24.1% (baseline) to 0.9% (endpoint). Using random-intercept multiple logistic regression, the relative odds of bug infection strongly decreased as the intervention period progressed, and increased with baseline domestic infestation and bug stage and in Qom households. The abundance of infected bugs and the proportion of houses with ≥ 1 infected bug remained depressed postintervention and were more informative of area-wide risk status than the prevalence of bug infection. Global spatial analysis revealed sharp changes in the aggregation of bug infection after the attack phase. Baseline domestic infestation and baseline bug infection strongly predicted the future occurrence of bug infection, as did persistent domestic infestation in the area with multiple pyrethroid-resistant foci. Only 19% of houses had a baseline domestic infestation and 56% had ever had ≥ 1 infected bug.

CONCLUSIONS

Persistent bug infection postintervention was closely associated with persistent foci generated by pyrethroid resistance. Postintervention parasite-based indices closely agreed with human serosurveys at the study endpoint, suggesting transmission blockage. The program identified households and population subgroups for targeted interventions and opened new opportunities for risk prioritization and sustainable vector control and disease prevention.

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.

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.

Triatoma rosai sp. nov. (Hemiptera, Triatominae): A New Species of Argentinian Chagas Disease Vector Described Based on Integrative Taxonomy

Simple Summary

Although all triatomines are potential vectors of Chagas' disease, there are species with greater or lesser vectorial importance. Therefore, the correct identification of triatomines species is essential for the vector control programs. In general, triatomines are identified by external morphological characters. However, some species are very similar or even morphologically identical, being important the use of complementary analyses for the correct identification of species. For this reason, this study focused on the use of morphological, morphometric, molecular data, and experimental crosses to describe Triatoma rosai sp. nov., a new species of Argentinian Chagas disease vector. Significant morphological and morphometric differences, associated with phylogenetic support and high mortality rate of the hybrids made it possible to confirm the specific status of T. rosai sp. nov., emphasizing the importance of integrative analyses for the taxonomy of triatomines.

Abstract

Chagas disease is the most prevalent neglected tropical disease in the Americas and makes an important contribution to morbidity and mortality rates in countries where it is endemic since 30 to 40% of patients develop cardiac diseases, gastrointestinal disorders, or both. In this paper, a new species of the genus Triatoma is described based on specimens collected in the Department San Miguel, Province of Corrientes, Argentina. Triatoma rosai sp. nov. is closely related to T. sordida (Stål, 1859), and was characterized based on integrative taxonomy using morphological, morphometric, molecular data, and experimental crosses. These analyses, combined with data from the literature (cytogenetics, electrophoresis pattern, molecular analyses, cuticular hydrocarbons pattern, geometric morphometry, cycle, and average time of life as well as geographic distribution) confirm the specific status of T. rosai sp. nov. Natural Trypanosoma cruzi infection, coupled with its presence mostly in peridomestic habitats, indicates that this species can be considered as an important Chagas disease vector from Argentina.

Impacts of residual insecticide spraying on the abundance and habitat occupancy of Triatoma sordida and co-occurrence with Triatoma infestans: A three-year follow-up in northeastern Argentina

Triatoma infestans, the main vector in the Gran Chaco region, may competitively displace other sympatric species such as Triatoma sordida. We conducted a three-year longitudinal study of site- and house-level infestation and abundance of triatomine bugs before and after an area-wide insecticide spraying campaign followed by sustained vector surveillance in a well-defined rural section of the Argentine Chaco encompassing 368-411 houses. Here, we tested whether insecticide applications targeting and virtually suppressing T. infestans reduced the abundance of T. sordida and modified its habitat occupancies, and whether their joint spatial distribution was random, aggregated or uniform, and varied over time. Systematic timed-manual searches of 18,031 sites yielded 2,226 T. sordida over seven postintervention surveys. Triatoma sordida failed to colonize human sleeping quarters after interventions, and its prime and secondary habitats remained virtually unmodified. Residual insecticide spraying and seasonality best described variations in the house-level abundance of T. sordida as determined using a generalized estimating equation model. Two-species foci occurred in 3.2% of sites ever positive for any species. The habitat-adjusted relative odds of catching one species was 10.8 times greater when the other species was present, with no evidence of heterogeneity among ORs, suggesting no antagonistic interactions throughout the follow-up. The spatial occurrence of both species was significantly aggregated within 300-500 m before and after interventions, and was random at broader spatial scales. The habitat occupancies of T. sordida may be used as a proxy for potential infestation with T. infestans and to guide targeted vector control actions.

New human isolates of Trypanosoma cruzi confirm the predominance of hybrid lineages in domestic transmission cycle of the Argentinean Chaco

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

Occurrences of triatomines (Hemiptera: Reduviidae) and first reports of Panstrongylus geniculatus in urban environments in the city of Sao Paulo, Brazil

This note reports on occurrences of triatomine species in the city of Sao Paulo, Brazil, registered between 1988 and 2017. Records of triatomines captured in Sao Paulo are based on specimens received spontaneously from Health Surveillance Centers, Health Centers and Zoonosis Control Centers in the city as well as from citizens. Species were identified morphologically at the Public Health Entomology Laboratory, Faculty of Public Health, University of Sao Paulo, where the triatomines, which are vectors of Chagas disease, were tested for Trypanosoma cruzi infection. The first reported occurrence of triatomine bugs in urban Sao Paulo was in 1988. The specimen, which was captured in Jardim Sao Luiz district, was from the genus Panstrongylus and was registered as Panstrongylus sp. but was not sexed. Since this first recorded occurrence, the following species have been found in the city: Panstrongylus geniculatus (2 occurrences), P. megistus (15 occurrences), Triatoma infestans (1 occurrence) and T. sordida (3 occurrences). In this paper, the importance of reporting occurrences of triatomine bugs in the city of Sao Paulo, one of the largest metropolis in the world, is discussed with an emphasis on P. megistus. The occurrences discussed here indicate the importance of entomological surveillance for these vectors even in urban centers although the possibility of vector transmission of Chagas disease in these centers is very low.

Habitat-Specific Occupancy and a Metapopulation Model of Triatoma sordida (Hemiptera: Reduviidae), a Secondary Vector of Chagas Disease, in Northeastern Argentina

Triatoma sordida Stål (Hemiptera: Reduviidae), a secondary vector of Trypanosoma cruzi Chagas (Kinetoplastida: Trypanosomatidae), occasionally colonizes human sleeping quarters in Paraguay, Bolivia, and Brazil, whereas only sylvatic and peridomestic populations are found in Argentina. We carried out a cross-sectional survey of house infestation in a well-defined rural area of northeastern Argentina to identify the key habitats of T. sordida; describe its spatial distribution in an apparently undisturbed setting under no recent insecticide treatment and use metapopulation theory to investigate these spatially structured populations. Timed-manual searches in 2,177 georeferenced sites from 368 houses yielded T. sordida in 78 sites (house infestation prevalence, 19.9%). Most triatomines occurred in chicken nests, chicken coops, and trees where chickens roosted (prime habitats). Goat or sheep corrals and pig corrals had a lower fraction of occupied sites (occupancies) and abundance. Both occupancy and catch increased with increasing refuge availability according to multimodel inference with model averaging. The majority of suitable habitats were unoccupied despite their proximity to occupied sites. The site-specific occurrence of T. sordida and Triatoma infestans Klug (Hemiptera: Reduviidae) was positively and homogeneously associated over ecotopes, showing no evidence of interspecific interference. An incidence function metapopulation model (including intersite distances and vector carrying capacity) predicted a fivefold greater occupancy relative to the observed pattern, suggesting the latter represented a transient state. T. sordida failed to colonize human sleeping quarters, thrived in peridomestic habitats occupied by chickens, and had a limited occupancy likely related to a poor colonizing ability and the relative instability of its prime habitats.

Triatoma costalimai (Hemiptera: Reduviidae) in and Around Houses of Tocantins State, Brazil, 2005-2014

Triatoma costalimai Verano & Galvão, a little-known vector of Trypanosoma cruzi Chagas, occupies rocky environments in the Brazilian Cerrado and occasionally infests man-made habitats. Entomological surveillance records show that T. costalimai occurs fairly often inside and around houses in south-eastern Tocantins, Brazil, with 859 specimens reported in 2005-2014. Most adults were caught indoors, and breeding colonies were found inside and around houses. Trypanosoma cruzi was detected in 13.7% of 839 bugs. These data suggest that T. costalimai can contribute to T. cruzi transmission in human environments, underscoring the need for long-term entomological-epidemiological surveillance wherever native Chagas disease vectors occur.

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.

Wing geometry of Triatoma sordida (Hemiptera: Reduviidae) populations from Brazil

Triatoma sordida has a widespread distribution in Argentina, Bolivia, Brazil, Paraguay, and Uruguay and is frequently found in peridomestic environments. We investigated size and shape variability of T. sordida wings across Brazil. Field-collected adults from twelve populations were studied. For each individual female, seven landmarks on the right wing were digitalized. Shape variables derived from Procrustes superimposition were used in Principal Component Analysis (PCA). Wing size and shape variations among populations was explored by means of ANOVA. Wing centroid size was significantly different among T. sordida populations; specimens from Bahia (East) were larger than those of Mato Grosso do Sul (West). PCA based on wing shape variables showed low wing shape variability. These results reinforce previous data showing low genetic variability among T. sordida populations from Brazil.

Host-Feeding Sources and Infection With Trypanosoma cruzi of Triatoma infestans and Triatoma eratyrusiformis (Hemiptera: Reduviidae) From the Calchaqui Valleys in Northwestern Argentina

We assessed the prevalence of infection with Trypanosoma cruzi, parasite genotypes (discrete typing units, DTUs), and the host-feeding sources of domestic and peridomestic Triatoma infestans Klug and Triatoma eratyrusiformis Del Ponte in eight rural communities of the subandean Calchaqui valleys in northwestern Argentina. We sought to analyze their epidemiological role in the context of routine vector surveillance and control actions. Infection with T. cruzi was determined by optic microscopy or polymerase chain reaction (PCR) amplification of the hypervariable region of kinetoplast DNA minicircles. Parasite genotypes were identified through a multi PCR-based strategy. Bloodmeal contents were tested with a direct ELISA assay against nine antisera. Human sleeping quarters (domiciles) and peridomestic dry-shrub fences concentrated most of the T. infestans and T. eratyrusiformis infected with T. cruzi, respectively. The most frequent host-feeding sources of T. infestans were chickens (73.1%) in peridomiciles and humans (73.3%) in domiciles, whereas T. eratyrusiformis fed more often on cavid rodents (92.6%), which thrived in the dry-shrub fences. The main T. cruzi DTU identified in both vectors was T. cruzi I (TcI). Triatoma eratyrusiformis was implicated in the local circulation of TcI among cavies and perhaps mice, but infection with other typically domestic DTUs (TcVI and TcII/TcV/TcVI) indicated overlap between (peri)domestic transmission cycles in both vector species. Because dry-shrub fences were not targeted for routine insecticide spraying, they may act as sources of (peri)domestic reinfestation. Triatoma eratyrusiformis is an emergent secondary vector of T. cruzi and plays a significant role in the local transmission of T. cruzi.

A comparative study of Trypanosoma cruzi infection in sylvatic mammals from a protected and a disturbed area in the Argentine Chaco

Understanding the complex epidemiology of Trypanosoma cruzi transmission cycles requires comparative studies in widely different environments. We assessed the occurrence of T. cruzi infection in sylvatic mammals, their infectiousness to the vector, and parasite genotypes in a protected area of the Argentine Chaco, and compared them with information obtained similarly in a nearby disturbed area. A total of 278 mammals from >23 species in the protected area were diagnosed for T. cruzi infection using xenodiagnosis, kDNA-PCR and nuclear satellite DNA-PCR (SAT) from blood samples. The relative abundance and species composition differed substantially between areas. Didelphis albiventris opossums were less abundant in the protected area; had a significantly lower body mass index, and a stage structure biased toward earlier stages. The capture of armadillos was lower in the protected area. The composite prevalence of T. cruzi infection across host species was significantly lower in the protected area (11.1%) than in the disturbed area (22.1%), and heterogeneous across species groups. The prevalence of infection in D. albiventris and Thylamys pusilla opossums was significantly lower in the protected area (nil for D. albiventris), whereas infection in sigmodontine rodents was three times higher in the protected area (17.5 versus 5.7%). Parasite isolates from the two xenodiagnosis-positive mammals (1 Dasypus novemcinctus and 1 Conepatus chinga) were typed as TcIII; both specimens were highly infectious to Triatoma infestans. Fat-tailed opossums, bats and rodents were kDNA-PCR-positive and xenodiagnosis-negative. Desmodus rotundus and Myotis bats were found infected with T. cruzi for the first time in the Gran Chaco.

Reservoir host competence and the role of domestic and commensal hosts in the transmission of Trypanosoma cruzi

We review the epidemiological role of domestic and commensal hosts of Trypanosoma cruzi using a quantitative approach, and compiled >400 reports on their natural infection. We link the theory underlying simple mathematical models of vector-borne parasite transmission to the types of evidence used for reservoir host identification: mean duration of infectious life; host infection and infectiousness; and host-vector contact. The infectiousness of dogs or cats most frequently exceeded that of humans. The host-feeding patterns of major vectors showed wide variability among and within triatomine species related to their opportunistic behavior and variable ecological, biological and social contexts. The evidence shows that dogs, cats, commensal rodents and domesticated guinea pigs are able to maintain T. cruzi in the absence of any other host species. They play key roles as amplifying hosts and sources of T. cruzi in many (peri)domestic transmission cycles covering a broad diversity of ecoregions, ecotopes and triatomine species: no other domestic animal plays that role. Dogs comply with the desirable attributes of natural sentinels and sometimes were a point of entry of sylvatic parasite strains. The controversies on the role of cats and other hosts illustrate the issues that hamper assessing the relative importance of reservoir hosts on the basis of fragmentary evidence. We provide various study cases of how eco-epidemiological and genetic-marker evidence helped to unravel transmission cycles and identify the implicated hosts. Keeping dogs, cats and rodents out of human sleeping quarters and reducing their exposure to triatomine bugs are predicted to strongly reduce transmission risks.