Urban vectors of Chagas disease in the American continent: A systematic review of epidemiological surveys

BACKGROUND

Chagas is a complex and multidimensional socio-environmental health phenomenon, in which different components converge and interact. Historically, this disease was associated with insect vectors found in the rural environment. However, in the Americas, we are currently facing a new paradigm, in which different scenarios allow maintaining the vectorial transmission of the parasite through triatomine populations that either occasionally enter the dwellings or colonize urban environments.

METHODOLOGY/PRINCIPAL FINDINGS

Records of scientific reports available in the PubMed and LILACS search engines were retrieved, using three criteria according to the main triatomine genera of epidemiological importance and to the general scientific production on Chagas disease in urban contexts. Results showed that records on the occurrence of vectors in urban dwellings began to increase in the last three decades. Results also showed that the main species of triatomines collected inside dwellings (18 in total) belong mainly to the genera Triatoma and Panstrongylus, with most species (16/18, 88.8%) infected with the parasite, and that infestation of triatomine species occurs in all types of cities (small, medium and large, including megalopolises), from Argentina to the USA.

CONCLUSIONS/SIGNIFICANCE

Urban Chagas represents a new challenge that adds a different dimension to the problem of Chagas disease due to the particular characteristics of the lifestyle in urban agglomerates. The new scenario will require adaptations of the programs of control of vector to this shift from rural to urban settlements.

Multiple Discrete Typing Units of Trypanosoma cruzi Infect Sylvatic Triatoma dimidiata and Panstrongylus rufotuberculatus in Southeast Mexico

Chagas disease or American trypanosomiasis is an infection caused by the parasite Trypanosoma cruzi. According to its genetic characteristics, this parasite is divided into six groups (TcI-TcVI) called discrete typing units (DTUs). Trypanosoma cruzi is transmitted to humans by insects of the Triatominae family. In Mexico, despite having a great variety of triatomine species, little is known about vector sylvatic populations and the DTUs associated with them. In this work, molecular markers such as minicircle, miniexon, 18S, and 24S ribosomal genes and restriction fragment length polymorphism (RFLP) analysis of the hsp70 gene were used to determine the DTUs present in vectors from rural communities and sylvatic areas inside the Biosphere Reserve Los Tuxtlas, Veracruz, in southeast Mexico. One hundred triatomines were collected and two species were identified: Triatoma dimidiata and Panstrongylus rufotuberculatus. The infection with T. cruzi was determined in 29% of analyzed vectors from the domestic area and TcI was the predominant DTU. Furthermore, 71% of vectors from the sylvatic environment were infected and TcI, TcII, TcIV, and TcVI were identified. One female and one male of P. rufotuberculatus were infected only with TcI. This is the first report of TcVI in T. dimidiata from the sylvatic area in México and the first report of P. rufotuberculatus infected with T. cruzi in Mexico.

Machine-learning model led design to experimentally test species thermal limits: The case of kissing bugs (Triatominae)

Species Distribution Modelling (SDM) determines habitat suitability of a species across geographic areas using macro-climatic variables; however, micro-habitats can buffer or exacerbate the influence of macro-climatic variables, requiring links between physiology and species persistence. Experimental approaches linking species physiology to micro-climate are complex, time consuming and expensive. E.g., what combination of exposure time and temperature is important for a species thermal tolerance is difficult to judge a priori. We tackled this problem using an active learning approach that utilized machine learning methods to guide thermal tolerance experimental design for three kissing-bug species: Triatoma infestans, Rhodnius prolixus, and Panstrongylus megistus (Hemiptera: Reduviidae: Triatominae), vectors of the parasite causing Chagas disease. As with other pathogen vectors, triatomines are well known to utilize micro-habitats and the associated shift in microclimate to enhance survival. Using a limited literature-collected dataset, our approach showed that temperature followed by exposure time were the strongest predictors of mortality; species played a minor role, and life stage was the least important. Further, we identified complex but biologically plausible nonlinear interactions between temperature and exposure time in shaping mortality, together setting the potential thermal limits of triatomines. The results from this data led to the design of new experiments with laboratory results that produced novel insights of the effects of temperature and exposure for the triatomines. These results, in turn, can be used to better model micro-climatic envelope for the species. Here we demonstrate the power of an active learning approach to explore experimental space to design laboratory studies testing species thermal limits. Our analytical pipeline can be easily adapted to other systems and we provide code to allow practitioners to perform similar analyses. Not only does our approach have the potential to save time and money: it can also increase our understanding of the links between species physiology and climate, a topic of increasing ecological importance.

Systematic review on the biology, ecology, genetic diversity and parasite transmission potential of Panstrongylus geniculatus (Latreille 1811) in Latin America

Panstrongylus geniculatus (Latreille, 1811) is the triatomine with the largest geographic distribution in Latin America. It has been reported in 18 countries from southern Mexico to northern Argentina, including the Caribbean islands. Although most reports indicate that P. geniculatus has wild habitats, this species has intrusive habits regarding human dwellings mainly located in intermediate deforested areas. It is attracted by artificial light from urban and rural buildings, raising the risk of transmission of Trypanosoma cruzi. Despite the wide body of published information on P. geniculatus, many knowledge gaps exist about its biology and epidemiological potential. For this reason, we analysed the literature for P. geniculatus in Scopus, PubMed, Scielo, Google Scholar and the BibTriv3.0 databases to update existing knowledge and provide better information on its geographic distribution, life cycle, genetic diversity, evidence of intrusion and domiciliation, vector-related circulating discrete taxonomic units, possible role in oral T. cruzi transmission, and the effect of climate change on its biology and epidemiology.

Spatial prediction of risk areas for vector transmission of Trypanosoma cruzi in the State of Paraná, southern Brazil

After obtaining certification of the absence of transmission of the Trypanosoma cruzi by Triatoma infestans in 2006, other native species of protozoan vectors have been found in human dwellings within municipalities of the State of Paraná, Southern Brazil. However, the spatial distribution of T. cruzi vectors and how climatic and landscape combined variables explain the distribution are still poorly understood. The goal of this study was to predict the potential distribution of T. cruzi vectors as a proxy for Chagas disease transmission risk using Ecological Niche Models (ENMs) based on climatic and landscape variables. We hypothesize that ENM based on both climate and landscape variables are more powerful than climate-only or landscape-only models, and that this will be true independent of vector species. A total of 2,662 records of triatomines of five species were obtained by community-based entomological surveillance from 2007 to 2013. The species with the highest number of specimens was Panstrongylus megistus (73%; n = 1,943), followed by Panstrongylus geniculatus (15.4%; 411), Rhodnius neglectus (6.0%; 159), Triatoma sordida (4.5%; 119) and Rhodnius prolixus (1.1%; 30). Of the total, 71.9% were captured at the intradomicile. T. cruzi infection was observed in 19.7% of the 2,472 examined insects. ENMs were generated based on selected climate and landscape variables with 1 km2 spatial resolution. Zonal statistics were used for classifying the municipalities as to the risk of occurrence of synanthropic triatomines. The integrated analysis of the climate and landscape suitability on triatomines geographical distribution was powerful on generating good predictive models. Moreover, this showed that some municipalities in the northwest, north and northeast of the Paraná state have a higher risk of T. cruzi vector transmission. This occurs because those regions present high climatic and landscape suitability values for occurrence of their vectors. The frequent invasion of houses by infected triatomines clearly indicates a greater risk of transmission of T. cruzi to the inhabitants. More public health attention should be given in the northern areas of the State of Paraná, which presents high climate and landscape suitabilities for the disease vectors. In conclusion, our results-through spatial analysis and predictive maps-showed to be effective in identifying areas of potential distribution and, consequently, in the definition of strategic areas and actions to prevent new cases of Chagas' disease, reinforcing the need for continuous and robust surveillance in these areas.

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.

Community-Based Entomological Surveillance Reveals Urban Foci of Chagas Disease Vectors in Sobral, State of Ceará, Northeastern Brazil

Background

The aim of this work was to explore the potential risk of vector-borne Chagas disease in urban districts in northeastern Brazil, by analyzing the spatiotemporal distributions and natural infection rates with Trypanosoma cruzi of triatomine species captured in recent years. The main motivation of this work was an acute human case of Chagas disease reported in 2008 in the municipality of Sobral.

Methodology/principal findings

We analyzed data from community-based entomological surveillance carried out from 2010 to 2014. Triatomine natural T. cruzi infection was assessed by examination of insect feces by optical microscopy. Sites of triatomine capture were georeferenced through Google Earth and analyzed with ArcGIS. A total of 191 triatomines were collected, consisting of 82.2% Triatoma pseudomaculata, 7.9% Rhodnius nasutus, 5.8% T. brasiliensis, 3.7% Panstrongylus lutzi, and 0.5% P. megistus, with an overall natural infection index of 17.8%. Most infestations were reported in the districts of Dom José (36.2%), Padre Palhano (24.7%), and Alto do Cristo (10.6%). The overwhelming majority of insects (185/96.9%) were captured inside houses, and most insects tended to be collected in intermittent peaks. Moreover, captured triatomines tended to constitute colonies. The acute case reported in 2008 was found to be situated within a T. pseudomaculata hotspot.

Conclusion

The triatomine collection events carried out by dwellers were aggregated in time and space into distinct foci, suggesting that insects are intermittently and artificially introduced into the city, possibly via accidental migration from their natural reservoirs. The relatively high T. cruzi infection rate indicates considerable circulation of the parasite in these areas, increasing the risk of vector-borne Chagas disease infection. These data suggest a need to strengthen epidemiological surveillance and integrate appropriate control actions targeting triatomines, T. cruzi reservoirs, and human populations. Our data also identify Chagas disease transmission as a hazard in urban areas of Sobral.

On palms, bugs, and Chagas disease in the Americas

Palms are ubiquitous across Neotropical landscapes, from pristine forests or savannahs to large cities. Although palms provide useful ecosystem services, they also offer suitable habitat for triatomines and for Trypanosoma cruzi mammalian hosts. Wild triatomines often invade houses by flying from nearby palms, potentially leading to new cases of human Chagas disease. Understanding and predicting triatomine-palm associations and palm infestation probabilities is important for enhancing Chagas disease prevention in areas where palm-associated vectors transmit T. cruzi. We present a comprehensive overview of palm infestation by triatomines in the Americas, combining a thorough reanalysis of our published and unpublished records with an in-depth review of the literature. We use site-occupancy modeling (SOM) to examine infestation in 3590 palms sampled with non-destructive methods, and standard statistics to describe and compare infestation in 2940 palms sampled by felling-and-dissection. Thirty-eight palm species (18 genera) have been reported to be infested by ∼39 triatomine species (10 genera) from the USA to Argentina. Overall infestation varied from 49.1-55.3% (SOM) to 62.6-66.1% (dissection), with important heterogeneities among sub-regions and particularly among palm species. Large palms with complex crowns (e.g., Attalea butyracea, Acrocomia aculeata) and some medium-crowned palms (e.g., Copernicia, Butia) are often infested; in slender, small-crowned palms (e.g., Euterpe) triatomines associate with vertebrate nests. Palm infestation tends to be higher in rural settings, but urban palms can also be infested. Most Rhodnius species are probably true palm specialists, whereas Psammolestes, Eratyrus, Cavernicola, Panstrongylus, Triatoma, Alberprosenia, and some Bolboderini seem to use palms opportunistically. Palms provide extensive habitat for enzootic T. cruzi cycles and a critical link between wild cycles and transmission to humans. Unless effective means to reduce contact between people and palm-living triatomines are devised, palms will contribute to maintaining long-term and widespread, albeit possibly low-intensity, transmission of human Chagas disease.

Comprehensive Survey of Domiciliary Triatomine Species Capable of Transmitting Chagas Disease in Southern Ecuador

BACKGROUND

Chagas disease is endemic to the southern Andean region of Ecuador, an area with one of the highest poverty rates in the country. However, few studies have looked into the epidemiology, vectors and transmission risks in this region. In this study we describe the triatomine household infestation in Loja province, determine the rate of Trypanosoma cruzi infection in triatomines and study the risk factors associated with infestation.

METHODOLOGY/PRINCIPAL FINDINGS

An entomological survey found four triatomine species (Rhodnius ecuadoriensis, Triatoma carrioni, Panstrongylus chinai, and P. rufotuberculatus) infesting domiciles in 68% of the 92 rural communities examined. Nine percent of domiciles were infested, and nymphs were observed in 80% of the infested domiciles. Triatomines were found in all ecological regions below 2,200 masl. We found R. ecuadoriensis (275 to 1948 masl) and T. carrioni (831 to 2242 masl) mostly in bedrooms within the domicile, and they were abundant in chicken coops near the domicile. Established colonies of P. chinai (175 to 2003 masl) and P. rufotuberculatus (404 to 1613 masl) also were found in the domicile. Triatomine infestation was associated with surrogate poverty indicators, such as poor sanitary infrastructure (lack of latrine/toilet [w = 0.95], sewage to environment [w = 1.0]). Vegetation type was a determinant of infestation [w = 1.0] and vector control program insecticide spraying was a protective factor [w = 1.0]. Of the 754 triatomines analyzed, 11% were infected with Trypanosoma cruzi and 2% were infected with T. rangeli.

CONCLUSIONS/SIGNIFICANCE

To date, only limited vector control efforts have been implemented. Together with recent reports of widespread sylvatic triatomine infestation and frequent post-intervention reinfestation, these results show that an estimated 100,000 people living in rural areas of southern Ecuador are at high risk for T. cruzi infection. Therefore, there is a need for a systematic, sustained, and monitored vector control intervention that is coupled with improvement of socio-economic conditions.

Detection of high percentage of Trypanosoma cruzi infection, the etiologic agent of Chagas disease, in wild populations of Colombian Caribbean triatomines

In Colombia it is estimated that about 900,000 persons are infected with T. cruzi. There are 25 triatomine species and 5 of them have been reported infected with T. cruzi in the Colombian Caribbean region. In order to obtain more information about the triatomine populations in this region, 89 wild triatomines were collected from four Colombian Departments. The most frequent specie collected was Rhodnius pallescens (65%), followed by Rhodnius prolixus (20%), Panstrongylus geniculatus (10.1%) and Triatoma dimidiata (1%), found in Bolivar, Córdoba, Atlántico/Sucre, and Bolívar Departments, respectively. The majority of triatomines (95.5%) were captured in the arboreal ecotope and 76.4% were found infected with T. cruzi. Interestingly, some of these triatomine species were captured in Departments in which they had not previously been reported and also new finding of triatomine species infected with T. cruzi. These results are relevant, because they can be consequence of a continued geographical expansion of this parasite, not only in the Colombian Caribbean region, but even in all Latin America. The information presented here will contribute in the surveillance and control strategies of the vectors infected with T. cruzi that circulate in four department of Colombian Caribbean region in order to interrupt the transmission to human dwelling.

Prevalence and Transmission of Trypanosoma cruzi in People of Rural Communities of the High Jungle of Northern Peru

Background

Vector-borne transmission of Trypanosoma cruzi is seen exclusively in the Americas where an estimated 8 million people are infected with the parasite. Significant research in southern Peru has been conducted to understand T. cruzi infection and vector control, however, much less is known about the burden of infection and epidemiology in northern Peru.

Methodology

A cross-sectional study was conducted to estimate the seroprevalence of T. cruzi infection in humans (n=611) and domestic animals [dogs (n=106) and guinea pigs (n=206)] in communities of Cutervo Province, Peru. Sampling and diagnostic strategies differed according to species. An entomological household study (n=208) was conducted to identify the triatomine burden and species composition, as well as the prevalence of T. cruzi in vectors. Electrocardiograms (EKG) were performed on a subset of participants (n=90 T. cruzi infected participants and 170 age and sex-matched controls). The seroprevalence of T. cruzi among humans, dogs, and guinea pigs was 14.9% (95% CI: 12.2 – 18.0%), 19.8% (95% CI: 12.7- 28.7%) and 3.3% (95% CI: 1.4 – 6.9%) respectively. In one community, the prevalence of T. cruzi infection was 17.2% (95% CI: 9.6 - 24.7%) among participants < 15 years, suggesting recent transmission. Increasing age, positive triatomines in a participant's house, and ownership of a T. cruzi positive guinea pig were independent correlates of T. cruzi infection. Only one species of triatomine was found, Panstrongylus lignarius, formerly P. herreri. Approximately forty percent (39.9%, 95% CI: 33.2 - 46.9%) of surveyed households were infested with this vector and 14.9% (95% CI: 10.4 - 20.5%) had at least one triatomine positive for T. cruzi. The cardiac abnormality of right bundle branch block was rare, but only identified in seropositive individuals.

Conclusions

Our research documents a substantial prevalence of T. cruzi infection in Cutervo and highlights a need for greater attention and vector control efforts in northern Peru.

Chagas disease causes significant morbidity and mortality throughout Central and South America. The epidemiology and control of this disease is subject to unique regional particularities, including the behavior and ecology of the local insect vector species. Significant resources have been allocated towards research and control efforts in southern Peru, yet very little is known about the prevalence and epidemiology of Trypanosoma cruzi in northern Peru. Our study highlights significant T. cruzi infection in northern Peru and is one of the first to document substantial transmission by the insect Panstrongylus lignarius. Our results illustrate major gaps in knowledge and the need for public health interventions targeted at Chagas disease in the region of Cutervo Province of northern Peru.

Biological and molecular characterization of a Trypanosoma cruzi isolate obtained from Panstrongylus megistus captured in Sao Paulo State, Brazil

An isolate of Trypanosoma cruzi obtained from P. megistus captured in the peridomicile area of a home in Santo Antonio do Jardim city in the State of Sao Paulo, denominated T. cruzi Mogi, was characterized biologically and molecularly. The RFLP analysis of the D7 divergent domain in the 24Sα rDNA and of the mini-exon positioned the T. cruzi isolate within the TcI group. Phylogenetic analysis performed with the trypanosomatid barcode confirmed that the isolate belongs to the TcI group, with high homology to the 3014 c1 T.cruzi strain. The biological characterization of the isolate in rats showed a prepatent period of about 8 days, low parasitemia and tropism for cardiac, skeletal and colonic muscles. In Swiss mice the T. cruzi Mogi isolate showed a prepatent period of about 22 days, intermittent parasitemia in some animals, and tropism for cardiac and colonic muscles. Despite the inherent difficulty of identifying correlations amongst the molecular and biological characteristics of different T. cruzi groups, the tropism for colonic muscle demonstrated by T. cruzi Mogi represented a peculiarity of this isolate within the TcI group.

Hallazgo de Panstrongylus rufotuberculatus (Champion, 1899) (Hemiptera, Reduviidae, Triatominae) en ambiente domiciliario en la Región Piura, Perú

Panstrongylus rufotuberculatus presenta una amplia distribución en América Central y del Sur con un comportamiento de especie silvestre. En el Perú ha sido registrado en Tumbes, Piura y Cuzco, siendo descrito en casas de localidades de este último departamento. En el presente trabajo se documenta evidencia de domiciliación de P. rufotuberculatus en la localidad de Chirinos-La Pareja, Distrito de Suyo, Provincia de Ayabaca, Región Piura, Perú (4º46'S, 79º93'W). Se capturaron 28 especímenes: 3 ninfas II, 4 ninfas III, 2 ninfas IV, 8 ninfas V, 3 machos y 8 hembras, lo que evidencia la existencia de una colonia intradomiciliar en "cuyeros" (criaderos de Cavia porcellus) camas y paredes del dormitorio de la vivienda. Exámenes parasitológicos de heces evacuadas espontáneamente fueron negativos a infección natural por Trypanosoma cruzi. A pesar de que se ha reportado la presencia de P. rufotuberculatus en localidades de Tumbes y Piura, es la primera vez que se documenta su tendencia sinantrópica en la Región. La importancia de esta especie y posteriores investigaciones permitirán evaluar su etología y potencial vectorial de trypanosomiasis americana. Se recomienda una cuidadosa actividad de vigilancia entomo-epidemiológica para esta especie y las otras que coexisten simpátricamente, actualmente en esta región del norte de Perú.

Epidemiología de la enfermedad de Chagas en el municipio Andrés Eloy Blanco, Lara, Venezuela: infestación triatomínica y seroprevalencia en humanos

Se realizó un despistaje serológico y recolección de vectores en cuatro comunidades rurales del municipio Andrés Eloy Blanco, Estado Lara, Venezuela. La muestra fue escogida en forma sistemática y aleatoria basada en conglomerados familiares. Se muestrearon 869 habitantes para determinar anticuerpos anti-Trypanosoma cruzi y anti-Leishmania sp. por inmunofluorescencia indirecta, aceptando como positivo diluciones > a 1:32 para anticuerpos anti-T. cruzi no reactivos para antígenos de Leishmania sp., obteniendo una frecuencia de anticuerpos en la muestra de 6,9% (n = 60); de los cuales 46,66% son femeninos, 53,33% masculinos y 60% mayores de 40 años. Se observó que 5 (8,33%) de los seropositivos eran menores de 10 años y 10 (16,66%) menores de 20 años. Rhodnius prolixus y Panstrongylus geniculatus fueron los triatominos capturados, con índice de infestación de 1,9 y 10,54%, índice de colonización, del 0 y 18,18% en las viviendas infestadas e índice de infección a T. cruzi del 20 y 5,07%, respectivamente. Los resultados sugieren que existe una transmisión activa de la enfermedad de Chagas en el Municipio Andrés Eloy Blanco en las últimas dos décadas y que P. geniculatus está substituyendo a R. prolixus como vector de la enfermedad de Chagas.

Competitive displacement in Triatominae: the Triatoma infestans success

Brazil has just been certificated by Pan American Health Organization as 'free of Chagas disease transmission due to Triatoma infestans'. During the early 1980s, this species of blood-sucking bug alone was considered responsible for approximately 80% of Chagas disease transmission. But it was not always so. The species originally abundant in houses of central and eastern Brazil was Panstrongylus megistus, which seems to have been progressively displaced from houses by T. infestans during the past century. Indeed, T. infestans seems able to displace other Triatominae in artificial environments. Recent studies suggest that it might simply be because T. infestans feeds more efficiently than its Triatominae competitors.

Estudo das fontes alimentares de Panstrongylus lutzi (Neiva & Pinto, 1923) (Hemiptera: Reduviidae: Triatominae) no Estado do Ceará

Os autores utilizaram a técnica de precipitina para identificar as fontes alimentares de Panstrongylus lutzi (Neiva & Pinto, 1923) em 20 municípios do Estado do Ceará, Brasil. Os resultados detectaram a presença de sangue de oito diferentes fontes sanguíneas e alimentações mistas, demonstrando que Panstrongylus lutzi é uma espécie eclética. Altas taxas de infecção por tripanosomatídeos foram detectadas.

[Rupestrian triatomines infected by Trypanosomatidae, collected in Quaraí, Rio Grande do Sul, 2003]

Rupestrian triatomines were captured in six Quaraí city localities, RS, to verify the level of Trypanosomatidae infection, as well as the animal reservoir. The capture occurred in a wild environment and 453 samples were collected, which were identified and separated by nymphal instar. 421 (92.9%) samples of Triatoma rubrovaria, 26 (5.7%) of Triatoma circummaculata and 6 (1.3%) of Panstrongylus tupynambai were collected. Only 13 samples (4.2%) of Triatoma rubrovaria presented Trypanosomatidae infection. After mice and LIT culture inoculation, five strains of Trypanosoma cruzi were isolated. Of these triatomines, 4 (30.8%) displayed no reagent precipitin for the antiserum tested, 4 (30.8%) were positive for rodent antiserum, 4 (30.8%) were positive for goat antiserum and 1 (7.7%) were positive for human and pig antiserum.

Infectivity for mice of Trypanosoma cruzi I and II strains isolated from different hosts

In this paper, the infectivity for mice of Trypanosoma cruzi I and II strains isolated from sylvatic animals, triatomines, and humans is determined using fresh blood examination, hemoculture, culture of macerated organs, and polymerase chain reaction (PCR). Six strains were considered to have low infectivity (9.1-18.2%), five medium (27.3-45.4%), and one high (100.0%). Infectivity of T. cruzi strains isolated from sylvatic animals was significantly higher than that of strains isolated from humans and triatomines (p=0.0141). No significant difference was observed between the infectivity of T. cruzi I and II strains. The parasite was detected by fresh blood examination in one strain, by hemoculture and culture of macerated organs in four strains, and by PCR in all strains. We conclude that the infectivity is related to the host from which the strains were isolated, but the infectivity is not related to the genetic group of the parasite. We also conclude that the majority of the strains studied have low and medium infectivity for mice, and that PCR is an important tool to detect T. cruzi in strains with this biological characteristic.

Risk of Trypanosoma cruzi I (Kinetoplastida: Trypanosomatidae) transmission by Panstrongylus geniculatus (Hemiptera: Reduviidae) in Caracas (Metropolitan District) and neighboring States, Venezuela

The collection of Panstrongylus geniculatus bugs by inhabitants of dwellings in Caracas city (Metropolitan District) and in the neighboring Miranda and Vargas Sates, Venezuela, allowed for the gathering of data on the potential role of this sylvatic triatomine bug as a vector of Chagas disease in this area. The natural infection by Trypanosoma cruzi was recorded by examining fresh and stained faeces of the bugs. Additionally, a random amplification of polymorphic DNA technique for parasite identification and group typing was employed. A dot-ELISA test was used to identify the gut content of the triatomine bugs with the aim of assessing and quantifying the vector-human contact. Sixty-seven specimens (76.1%) were positive to T. cruzi (identified as T. cruzi I) and 60.2% (53/88) gave a positive reaction to the human antiserum. The human blood-positive samples included mixed blood meals with domestic animals (dog, pig and cow) (9.4%) and with mouse (3.8%). The overall Human Blood Index, measured as the percentage of bugs whose gut contents reacted with human antiserum on the total numbers of bugs that reacted with all the antisera tested, was 98.1%. Almost 41% of the bugs that had fed on humans were also positive for T. cruzi. These data show that the feeding of P. geniculatus on humans does not seem to be accidental and that its rate of infection by T. cruzi is high in this area which is not regarded as endemic for Chagas disease by the National Control Programme. This situation is particularly striking because it occurs in and around Caracas, the capital city, where 20% of the whole population of Venezuela live, human migrations from endemic areas are continuous, people in the crowded shantytown as well as people living in high-quality country houses are equally at risk and the epidemiological cycle Didelphis marsupialis/Rattus rattus-P. geniculatus-human does appear to occur successfully.

Occurrence and variability of Panstrongylus lutzi in the State of Ceará, Brazil

Panstrongylus lutzi is generally restricted to the "caatinga" areas of north-eastern Brazil. Adult insects are frequently found in local houses, but colonies have not previously been registered in the statistics of the Control Programme of Chagas Disease. In Ceará State, our study revealed increasing occurrence of this species, usually with high infection rates for Trypanosoma cruzi, and always represented by adults that invaded the artificial environment. We also found nymphs in the peridomicile and inside the houses. In silvatic habitats we collected two adult females from hollow tree trunks, which may represent an alternative natural ecotope for the species in this state. Panstrongylus lutzi entomological collections from Sobral and Crateús, studied by morphology and morphometrics, showed great variability; those from Crateús were larger smaller and paler in colour, with individuals showing genital features consistent with those described for Panstrongylus lutzi or Panstrongylus sherlocki, whereas those from Sobral were darker and with genitalia compatible with P. sherlocki, nevertheless, all were considered to be Panstrongylus lutzi.

High household infestation rates by synanthropic vectors of Chagas disease in southern Ecuador

Entomological surveys were conducted in five rural communities (138 domiciliary units [DUs]) in the southern Andes of Ecuador. Adobe walls and ceramic tile roofs were predominant construction materials. A 35% house infestation rate with Panstrongylus chinai (Del Ponte, 1929) (0.7%), Panstrongylus rufotuberculatus (Champion, 1899) (0.7%), Rhodnius ecuadoriensis (Lent & León, 1958) (27%), and/or Triatoma carrioni (Larrousse, 1926) (7%) was found. Adults and nymphs of R. ecuadoriensis and T. carrioni were found in intradomiciliary and peridomiciliary areas. Breeding triatomine colonies were present in 85% of infested DUs, and the average insect crowding was 52+/-113 triatomine bugs per infested house. T. cruzi-like organisms were found by microscopic examination in the feces or hindgut but not the salivary glands of 4% of examined R. ecuadoriensis and 12% T. carrioni. Serological tests detected a general anti-T. cruzi antibody seroprevalence of 3.9% (n = 1136). Only 2% of individuals had heard of Chagas disease, and although triatomines were reported as a major nuisance by the population they were not considered vectors of disease. Additional baseline field research is needed for the design and implementation of a Chagas disease control program in the region.

Mixed domestic infestation by Rhodnius prolixus Stal, 1859 and Panstrongylus geniculatus Latreille, 1811, vector incrimination, and seroprevalence for Trypanosoma cruzi among inhabitants in El Guamito, Lara State, Venezuela

Mixed infestation of nymphs and adults of Rhodnius prolixus Stal, 1859 and Panstrongylus geniculatus Latreille, 1811 was detected in 3 (15%) of 20 dwellings in El Guamito, an endemic focus of Chagas disease in Lara State, Venezuela. In one of the houses, both species were positive for Trypanosoma cruzi: 14.3% (R. prolixus) and 20% (P. geniculatus ). The overall infection rate in 143 of 352 R. prolixus was 16.1%. Parasites isolated from R. prolixus were identified as T. cruzi I by random amplified polymorphic DNA analysis. Dot-enzyme-linked immunosorbent assays of 36 R. prolixus showed that 58.3% of the R. prolixus had fed on humans. The gut contents of one fifth-instar nymph of P. geniculatus that was positive for T. cruzi also reacted with anti-human serum. A questionnaire was used to gather data on the demographic and socioeconomic characteristics of the population. An indirect immunofluorescent test, an indirect hemaglutination test, and an ELISA were used to detect the presence of antibodies against T. cruzi in 84 of 86 inhabitants and in 15.5% of people more than 20 years old. The relative risk (RR) of infection was greater in men than in women (RR = 1.61, 95% confidence interval = 0.54-4.80). Of the people more than 15 years old, 36.6% had no formal education. All respondents recognized triatomine bugs, but they did not relate them to Chagas disease transmission. A total of 85.7% of the houses were "ranchos" suitable for the colonization of triatomine bugs. The possible domiciliation of P. geniculatus and the implications of competition with R. prolixus for resources are discussed. Since there is no clear separation of food sources, abiotic factors such as microclimatic variation within houses may be critical to predict the outcome of the process of competition and potential domestication of this generally sylvatic species.

[Occurrence of Panstrongylus lutzi, in peridomiciliary areas, State of Ceará, Brazil]

From January 2001 to October 2002 captures were made in domicile and peridomiciliary areas of 13 cities of region of Cariri, south of the State of Ceará. As results, the occurrence of P. lutzi in this area was noticed, for the first time, in three cities: the presence of one adult in chicken house in Altaneira, one adult flying, in Salitre and 18 nymphs in Varzea Alegre(13 in bricks pile and five in roofing tile pile). In Varzea Alegre city it was observed the colonization in the peridomicile.

High prevalence of Trypanosoma rangeli and Trypanosoma cruzi in opossums and triatomids in a formerly-endemic area of Chagas disease in Southeast Brazil

In Brazil Trypanosoma rangeli has been detected in humans, sylvatic mammals and vectors in the Amazon Basin and in wild rodents in a Southern State. Here we report for the first time a high prevalence of T. rangeli in opossums and triatomids captured in peridomestic environments in a formerly-endemic area of Chagas disease in Southeast Brazil. Five molecular typing tools clearly indicate the presence of T. rangeli and Trypanosoma cruzi in mammalian reservoirs and triatomids. Twenty-one opossums (Didelphis albiventris) were captured and flagellates were detected in the blood of 57.1% (12/21) of the animals. Single infections with T. rangeli or T. cruzi were diagnosed, respectively, in 58.4 and 8.3% of the opossums. Mixed infections were observed in 33.3%. Forty-four triatomids (38 Rhodnius neglectus and 6 Panstrongylus megistus) were collected in palm trees within 50 m from human dwellings. Flagellates were observed in the digestive tract and feces of 50% of the insects. PCR assays performed in DNA samples obtained from 16 cultures of the intestinal tract revealed single infection with T. cruzi (68.7%) or T. rangeli (6.3%), as well as mixed infections (25%). T. rangeli was also detected in the hemolymph of two specimens. Genotyping revealed predominance of T. cruzi I. The data suggest that R. neglectus in conjunction with D. albiventris may be significant factors in the maintenance of the sylvatic and peridomestic cycles of T. rangeli in the region. The finding of T. cruzi and T. rangeli in triatomine species capable of domiciliation and therefore considered as alternative vectors for the parasite transmission opens up the possibility of re-establishment of Chagas disease following reinfestation of houses.

Nuclear rDNA ITS-2 sequences reveal polyphyly of Panstrongylus species (Hemiptera: Reduviidae: Triatominae), vectors of Trypanosoma cruzi

Panstrongylus species are widely distributed throughout the Americas, where they act as vectors of Trypanosoma cruzi, agent of Chagas disease. Their intraspecific relationships, taxonomic position and phylogeny in relation to other Triatomini were explored using ribosomal DNA (rDNA) internal transcribed spacer 2 (ITS-2) sequence polymorphisms and maximum parsimony, distance and maximum likelihood analyses of 10 populations representing six species of the genus (P. megistus, P. geniculatus, P. rufotuberculatus, P. lignarius, P. herreri and P. chinai). At the subspecific level, P. megistus appeared more homogeneous than P. rufotuberculatus and P. geniculatus (both with broader distribution). Several dinucleotide microsatellites were detected in the sequences of given species. Many of these microsatellites (GC, TA, GT and AT) showed different number of repeats in different populations and thus, may be very useful for population differentiation and dynamics analyses in future studies. The sequences of P. lignarius (considered sylvatic) and P. herreri (a major disease vector in Peru) were identical, suggesting that these species should be synonymised. Intrageneric analysis showed a clear separation of P. rufotuberculatus, with closest relationships between P. geniculatus and P. chinai, and P. megistus occupying a separate branch. Genetic distances between Panstrongylus species (0.11585-0.22131) were higher than those between Panstrongylus and other Triatomini (16 species from central and North America and South America) (0.08617-0.11039). The distance between P. megistus and P. lignarius/herreri (0.22131) was the largest so far recorded in the tribe. The pronounced differences in length and nucleotide composition suggest a relatively old divergence of Panstrongylus species. P. rufotuberculatus was closer to Mesoamerican Triatoma, Meccus and Dipetalogaster species than to other Panstrongylus. All Panstrongylus clustered with the Mesoamerican clade; P. rufotuberculatus clustered with the phyllosoma complex and T. dimidiata, with D. maxima and T. barberi in a basal position. The rest of Panstrongylus appeared paraphyletically in the tree. This is evidence suggesting polyphyly within the genus Panstrongylus, whose species may be related to the ancestors giving rise to central and North American Triatomini.

Domiciliation trend of Panstrongylus rufotuberculatus in Colombia

The present paper presents evidence of the domiciliation of Panstrongylus rufotuberculatus in La Gardenia, Colombia through the collection of 2 unhatched eggs, 81 nymphs and 10 adults (4 males and 6 females), from 2 rural houses. The transmission risk indicators of Trypanosoma cruzi by P. rufotuberculatus in La Gardenia, were: domiciliary infestation 7.5%, density 2.35, colonization 66.6%, overcrowding 31.33, natural infection 4.6%, and relative infection 2.5%. These results and findings in Peru and Argentina, show that P. rufotuberculatus has a potential success in domiciliation and could some day become an alternate vector of American trypanosomiasis.

Trypanosoma cruzi infection in Didelphis marsupialis in Santa Catarina and Arvoredo Islands, southern Brazil

Between 1984 and 1993 the prevalence of the Trypanosoma cruzi infection in opossums (Didelphis marsupialis) was studied in Santa Catarina and Arvoredo Islands, State of Santa Catarina, Brazil. The association of the triatomine bug Panstrongylus megistus with opossums nests and the infection rate of these triatomines by T. cruzi was also studied. Thirteen different locations were studied in Santa Catarina Island (SCI), in which 137 D. marsupialis were collected. Sixty two opossums were collected at the Arvoredo Island (AI), located 12 miles north from SCI. All captured animals were submitted to parasitological examinations that revealed the presence of T. cruzi in 21.9% of the opossums captured in SCI and 45.2% among opossums captured in the AI. The presence of P. megistus was detected in most of the D. marsupialis nests collected in the SCI, however, in the non-inhabited AI only eight triatomines were collected during the whole study. The presence of T. cruzi-infected D. marsupialis associated with P. megistus in human dwellings in the SCI, and the high infection rate of D. marsupilais by T. cruzi in the absence of a high vector density are discussed.

Survey for Trypanosoma cruzi infection in a municipality in northeast Brazil

An epidemiological survey of Trypanosoma cruzi infection was carried out in Bodocó, located in the western part of the State of Pernambuco, Brazil. Two hundred and forty-one individuals were parasitologically and immunologically screened. Although hemoculture did not reveal the presence of parasites in the blood, the sera of 5 individuals were scored as positive by the indirect fluorescence antibody test and the enzyme-linked immunosorbent assay. Seropositivity in individuals above and below the age of 40 was 14.8 and 0.5%, respectively. These results indicate that recent infections with T. cruzi are rare in this area. However, since a T. cruzi-infected triatomid (Triatoma brasiliensis) was captured in a school classroom, this area must be considered endemic. When triatomid feces containing parasites were inoculated into a jird (mongolian gerbil), parasitemia appeared 10 days later. Immunohistochemical staining, using monoclonal antibody specific for T. cruzi, labeled organisms in jird tissues. These observations demonstrate that the jird is a suitable host for experimental T. cruzi infections and that monoclonal antibody is effective for detection of the parasite in host tissues.

Presence of Panstrongylus rufotuberculatus (Champion, 1899) (Hemiptera: Reduviidae: Triatominae) in Argentina

Panstrongylus rufotuberculatus is reported for the first time in Argentina. Four adults were attracted by the light of human dwellings in Calilegua National Park, Jujuy, at 1150 masl within the subtropical humid forest. The individuals were similar to those described in the literature. The epidemiological significance of this species is very low in the area, although deforestation might increase its role in the transmission of Trypanosoma cruzi.

Chagas disease in the Amazon Basin: association of Panstrongylus geniculatus (Hemiptera: Reduviidae) with domestic pigs

Just over 100 autochthonous cases of Chagas disease are reported from the Brazilian Amazon Basin. Panstrongylus geniculatus (Latreille) occurs throughout the region and is the known vector of Trypanosoma cruzi, principal zymodeme 3 (Z3) to the armadillo Dasypus novemcinctus. In the small riverine community of Furo do Rio Pau Grande, pigsties adjoining houses were heavily infested with P. geniculatus, which repeatedly attacked local inhabitants. Palm trees in the immediate vicinity were also infested. T. cruzi principal zymodeme 1 (Z1) was isolated from P. geniculatus, domestic pigs, and opossums, but no human infections were detected. The threat of endemic Chagas disease to the Amazon Basin from either domiciliation of local silvatic triatomine species, or from migration of domestic vectors, demands a program of vigilance and plans of action to eliminate household triatomine colonies.

[Wild vectors of Chagas' disease in an urban area of Manaus (AM): flying activity during dry and rainy seasons]

Adults of Rhodnius prolixus, R. pictipes and Panstrongylus geniculatus found in houses in Manaus have high rates of Trypanosoma cruzi infection. Rhodnius spp. were found throughout the year, but males of P. geniculatus were significantly more frequent in the dry season.

[The finding of Panstrongylus megistus in an artificial ecotope: taking up residence or merely visiting?]

As a first measure of Chagas' disease control in Brazil with chemical elimination of the most important vector of the disease, Triatoma infestans was removed. Attention is now being paid to Triatoma sordida and Panstrongylus megistus. That species can eventually be found inside houses, as happened with the specimens we examined from Bernardino de Campos and Sete Barras, all of them infected by Trypanosoma cruzi. These data suggest that a better knowledge about the behavior that species is needed to introduce changes in the control measures.

Characterization of Trypanosoma cruzi strains isolated from chronic chagasic patients, triatomines and opossums naturally infected from the State of Rio Grande do Sul, Brazil

Thirty-five Trypanosoma cruzi strains were isolated from chronic chagasic patients, triatomines and opossums from different municipalities of the State of Rio Grande do Sul. Parasites were characterized by means of mice infectivity, enzyme electrophoresis and randomly amplified polymorphic DNA (RAPD) analysis. Twenty-nine strains were isolated from chagasic patients, 4 from triatomines (2 from Triatoma infestans and 2 from Panstrongylus megistus) and 2 from opossums Didelphis albiventris. Thirty-three T. cruzi strains were of low and 2 strains of high virulence in mice. Both virulent strains were isolated from P. megistus. Isoenzyme analysis of the strains showed 3 different zymodemes. Eleven strains isolated from chagasic patients and 2 from D. albiventris were Z2. Eighteen strains from patients and 2 from T. infestans were ZB and 2 T. cruzi strains isolated from P. megistus were Z1. RAPD profiles obtained with 4 random primers showed a high genetic heterogeneity of the T. cruzi strains. Zymodeme 2 and ZB strains were the more polymorphic. A band sharing analysis of the RAPD profiles of Z2 and ZB strains using 3 primers, showed a very low percentage of shared bands, 20% among 13 ZB strains and 14% among 13 Z2 strains. According to the isoenzyme results, 3 T. cruzi populations were present in State of Rio Grande do Sul. Zymodeme 2 and ZB strains were found infecting man (domiciliar transmission cycle) whereas Z1 strains were found infecting the sylvatic vector P. megistus.

[Triatomids and forest reservoirs of Trypanosoma cruzi in the state of Paraná, southern Brazil. Preliminary results]

In the rural area of five municipalities of the Northeast of the State of Paraná, Brazil, 154 adults or nymphs of Triatoma sordida and 2 Panstrongylus megistus were captured in 21 (41.2%) of 51 dwellings at the peridomestic sites. Trypanosoma cruzi-like organisms were found in 58 out of the 135 (43.0%) triatomids. Moreover, it was also found in the blood of 4/7 opossum (Didelphis sp). The triatomine infestation was more prevalent in the peridomicile than inside house. The forsaken wooden house presented the highest level of infestation (53.8%). Although the rural area of the Northeast of the State of Paraná is considered under epidemiologic surveillance it still presents a high level of peridomestic infestation by triatomids highly infected with T. cruzi-like organisms.

Attempts to improve xenodiagnosis: comparative test of sensibility using Rhodnius neglectus, Panstrongylus megistus, Triatoma vitticeps and Triatoma infestans in endemic areas of Brazil

From June 1984 to July 1992, 392 xenodiagnostic tests were applied on 264 patients with chronic Chagas disease from Brazilian endemic areas of Virgem da Lapa and Coronel Murta, situated in the Jequitinhonha Valley, in the State of Minas Gerais. The susceptibilities of Rhodnius neglectus, Panstrongylus megistus, Triatoma vitticeps and Triatoma infestans were compared. Most of the time 20 nymphs (fourth instar) of each species were applied to 161 women and 103 men aged between 5 and 83 years of age. The tests were prepared to compare the susceptibilities of two species at a time, using the same patients for each test. Results showed a xenopositiveness of 26.28% (103 tests) being 27.98% in women (68 positive in 243 applied tests) and 23.49% in men (35 positive in 149 applied tests). The relative frequency of xenopositiveness displayed a great superiority of P. megistus and T. vitticeps. In tests from type 1, for example, P. megistus was the unique responsible for 10.73% of positive xenodiagnosis vs only 0.98% in T. infestans. Other parameters analized in this work confirm this superiority, and corroborate that T. infestans can be replaced by P. megistus and/or T. vitticeps in order to upgrade the efficacy of xenodiagnosis.

[Xenodiagnosis in chronic Chagas' disease. I. The sensitivity of Panstrongylus megistus and Triatoma infestans]

From January 1986 to February 1994, 563 xenodiagnosis (XD) were applied in 563 chronic chagasic patients from different areas of Brazil; 292 were women and 271 were men between 6 and 89 years (average: 41.4 +/- 14.7 years). To each XD 40 nymphs on the 4th stage were used: 20 from Panstrongylus megistus (Pm) and 20 from Triatoma infestans (Ti) in fast, during at least 14 days. The exam in each nymph was made 45 days after being applied on the patient, by observation in optical microscopy of the drugs and/or the grinded from the digestive tube. The results are: a) 205 (36.4%) positive XD, including 85 (15.1%) due only nymphs of Pm, 44 (7.8%) Ti and 76 (13.5%) Pm and Ti; b) positively in 4.9% of the nymphs from Pm and in 3.0% of the Ti nymphs examined. These results' analysis showed that the Pm nymphs were more sensitive that Ti's ones to the infection by Trypanosoma cruzi, increasing considerably the xenopositivity, independently from birthplace, sex or age of the patients. These results point out that to increase the efficacy of XD in chronic Chagas' disease, the exam must have more than a species of triatomine with different sensibilities to the T. cruzi infection, and in case of using one species on XD, Pm must substitute Ti.

The threat of reintroduction of natural transmission of Chagas' disease in Bambuí, Minas Gerais State, Brazil, due to Panstrongylus megistus

In the Epidemiological Surveillance Program in the county of Bambuí, Minas Gerais, between August 1986 and December 1988, 154 Panstrongylus megistus were captured by the local population in both peridomicile and intradomicile environments. Fifteen (9.8%) of the P. megistus harboured Trypanosoma cruzi. Precipitin tests showed that the most frequent triatomine blood meal sources were birds, but other sources were dogs, men and cats. The isoenzyme characterization of 13 T. cruzi strains showed that six belonged to zymodeme Z1, corresponding to the wild cycle parasites, and seven belonged to zymodeme Z2, corresponding to parasites isolated from chronic chagasic patients (domestic cycle). As P. megistus were found to be naturally infected by parasites from both cycles. They are clearly able to transmit T. cruzi from the wild cycle to the domestic cycle. Furthermore the capacity of P. megistus in colonizing houses was observed in one residence, vacant for several years, in which 153 triatomines were captured. The data show the possibility of P. megistus reintroducing the natural transmission of Chagas' disease in the county if Epidemiological Surveillance is interrupted.

Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with Chagas' disease. 4--The reflection of parasite stock in the responsiveness of different vector species to chronic infection with different Trypanosoma cruzi stocks

Previous studies (1982, 1987) have emphasized the superiority of sylvatic vector species over domestic species as xenodiagnostic agents in testing hosts with acute or chronic infections by T. cruzi "Y" stock. The present study, which is unique in that it contains data on both infectivity rates produced by the same stock in 11 different vector species and also the reaction of the same vector species to seven different parasite stocks, establishes the general validity of linking efficiency of xenodiagnosis to the biotope of its agent. For example, infectivity rates produced by "São Felipe" stock varied from 82.5% to 98.3% in sylvatic vectors but decreased to 42.5% to 71.3% in domestic species. "Colombiana"stock produced in the same sylvatic vectors infectivity rates ranging from 12.5% to 45%. These shrank to 5%-22.5% in domestic bugs. The functional role of the biotope in the vector-parasite interaction has not been elucidated. But since this phenomenon has been observed to be stable and easy to reproduce, it leads us to believe that the results obtained are valid. Data presented also provide increasing evidence that the infectivity rates exhibited by bugs from xenodiagnosis in chronic hosts, are parasite stock specific. For example, infectivity rates produced by "Berenice", "Y", "FL" and "CL" varied in R. neglectus from 26.3% to 75%; in P. megistus from 56.3% to 83.8%; in T. sordida from 28.8% to 58.8% in T. pseudomaculata from 41.3% to 66.3% and in T. rubrovaria from 48.8% to 85%. Data from xenodiagnosis in the same hosts, carrying acute infections by the same parasite stocks, gave the five sylvatic vectors a positive rating of approximately 100%, thus suggesting that the heavy loads of parasites circulating in the acute hosts obscured the characteristic interspecific differences for the parasite stock. Nonetheless these latter were revealed in the same hosts with chronic infections stimulated by very low numbers of the same parasite stocks. Certain observations here described lead us to speculate as to the possibility of further results from other parasite stocks, allowing the association of the infectivity rates produced in bugs by different parasite stocks with the isoenzymic patterns revealed by these stocks.

Urban Trypanosoma (Schizotrypanum) cruzi: pathology in white mice of isolates from Panstrongylus geniculatus

The histopathological alterations produced in white mice (NMRI strain) by isolates of Trypanosoma (Schizotrypanum) cruzi from Panstrongylus geniculatus captured in dwellings of the city of Caracas, Venezuela are reported. The heart, skeletal muscle, liver, spleen, duodenum, colon, lung, and brain were parasitized by all the isolates. All showed strong myotropism, with elevated virulence and severe histopathological alterations in the cardiac and skeletal muscle, and in the smooth muscle of the duodenum, colon, and lung; parasitization of the mononuclear phagocytic system was discrete. These results, in addition to the morphobiological characters reported in a previous paper, suggest that the isolates in question belong to the same type of parasite. The possible causes of this observation are discussed in the light of the heterogeneity of T. cruzi. The epidemiological significance of the existence of these parasite forms in the urban areas of Caracas is emphasized.

Electron microscope observations of Trypanosoma cruzi during development inside the haemocytes of Triatominae

The haemolymph of Panstrongylus megistus, infected by Trypanosoma cruzi, was examined by light and electron microscopy. Numerous parasites lie inside the haemocytes, each one in a vacuole. Their well-preserved morphological features support the concept of parasite multiplication in cells of the insect haemolymph.

Value of first-instar triatomines (Hemiptera; Reduviidae) in comparative xenodiagnosis of Trypanosoma (Schizotrypanum) cruzi

A direct correlation was shown between bloodmeal intake in xenodiagnosis and subsequent infection rate with Trypanosoma (S.) cruzi, in first-stage nymphs of Panstrongylus megistus Burmeister. The parasitaemia of different hosts, or of the same host at intervals, thus can be compared indirectly by the proportion of first-stage nymphs infected in xenodiagnosis, if uniform distribution and infectivity of bloodstream trypomastigotes is assumed. This indirect comparison of host parasitaemia provides important information not obtainable otherwise, since parasitaemia often is too low for quantitative measurement. Infection rates were compared of first-instar P. megistus in experimental xenodiagnosis of patients and animals. All T. cruzi stocks originated from an endemic area of Brazil (Bahia state). Several batches of nymphs were fed sequentially on some hosts, to assess fluctuations of parasitaemia with time; in others, particularly the patients, xenodiagnosis was carried out only once.

Association between household triatomine density and incidence of Trypanosoma cruzi infection during a nine-year study in Castro Alves, Bahia, Brazil

We studied the association between human incidence of Trypanosoma cruzi infection and household infestation density of Panstrongylus megistus in Castro Alves, Bahia, Brazil. During a 9-year period, 19 persons seroconverted; 17 were children, 17 lived in nonplastered houses, and 13 lived in houses infested with triatomines. Although 6 seroconverting persons lived in houses where triatomines could not be found, the risk of seroconversion was significantly greater in infested houses and 16 times greater in densely infested houses (greater than 15 bugs/person-hour of search). The highest rate of seroconversion (6/100 person-years exposure) occurred in houses containing the greatest number of bugs infected with T. cruzi (greater than 6 infected bugs/person-hour). These observations suggest that vector control measures could have a dramatic impact on transmission of T. cruzi by P. megistus.

Trypanosoma cruzi: kinetics of metacyclogenesis in adult and nymphal Panstrongylus megistus

Adult triatomine insects, Panstrongylus megistus, naturally infected with the protozoa, Trypanosoma cruzi, contained significantly more metacyclic trypomastigote forms in their digestive tracts than did P. megistus nymphs. Metacyclics were scarce in all stages of triatomines fed once on infected mammalian hosts and subsequently starved. In contrast, triatomines fed repeatedly on infected mammalian hosts developed prolific T. cruzi infections. Repeatedly fed adults contained 14 X more metacyclics than similarly fed nymphs. Nutritional factors appear to play a key role in regulating metacyclogenesis. Control campaigns designed to alter the age structure of populations of triatomines must take notice of the high transmission potential of the adult stage.

The development of extra-intestinal cycle of Trypanosoma cruzi in Triatoma infestans and Panstrongylus megistus

By applying various histological techniques the results obtained were similar to those in Lacombe's previous publications referring to the development of Trypanosoma cruzi in haemolymph, the later penetration in the Malpighian tubes and their return to the digestive tract. Trypomastigotes and sphaeromastigotes are found in the promesenteron after two hours of feeding the insect with mice blood containing numerous Trypanosoma cruzi. Some parasites move to the promesenteron from postmesenteron and others from the haemolymph of the insect. The amastigotes form inside the haemocytes, multiply, occupying nearly all the cells of the haemolymph. The parasites liberated inside the Malpighian tubes move to the ampullae where they begin their growth. The parasites in epimastigote and trypomastigote forms cross the pyloric valve and adhere to the folds of the rectum.

[Ecological aspects of South American trypanosomiasis. XX-- Development and annual cycles of Panstrongylus megistus colonies in artificial ecotopes, in peri- and extradomiciliary environments]

Em colônias de Panstrongylus megistus, espontaneamente desenvolvidas em galinheiros experimentais, pôde-se observar as condições de desenvolvimento, variação e permanência de seus componentes. Foram obtidos também dados sobre os ciclos anuais e a sobrevivência, O aspecto cíclico caracterizou-se pela maior produção de formas adultas no último trimestre do ano, ocasião que coincide com o encontro dessa espécie no ambiente domiciliar. Face a tais achados, considera-se que o período de produção de adultos representa a fase "infestante" para o ambiente domiciliar "suscetível", este representado pelas áreas tratadas, ou seja, as previamente submetidas ao expurgo. Nesse período, ocorre o risco da reinfestação e subseqüente domiciliação desse triatomíneo, a partir do ambiente extradomiciliar. Tais informações permitem sua utilização nas atividades de vigilância epidemiológica.

Factors controlling the volume of feces produced by triatomine vectors of Chagas' disease

Triatomine species influenced volume of feces produced; Triatoma dimidiata produced the largest volume of feces followed by Panstrongylus megistus, Rhodnius prolixus, and Triatoma infestans. Moreover, stage and sex affected fecal production; 5th-stage female nymphs excreted the largest volume of feces. The amount of blood ingested was significantly correlated with the volume of feces produced in 10 out of 11 experimental groups. Triatome size and volume of feces produced were less closely correlated. Indeed, a "threshold" minimum amount of blood must be ingested before bugs are stimulated to defecate. The defecation habits of triatomines probably influence the vectorial capacity of a triatomine species to a lesser degree than do the density of domestic infestations, host affinity, and the degree of adaptation to the domestic habitat.

[Ecological aspects of South American trypanosomiasis. XIX - Development of regional Triatominae domiciliation in an endemic center of Panstrongylus megistus]

São apresentados os resultados obtidos mediante as observações sobre o processo de domiciliação triatomínea em região incluída no domínio paisagístico Tropical Atlântico, considerado como centro de dispersão do Panstrongylus megistus. As observações foram levadas a efeito no período de março de 1976 a outubro de 1978, em áreas onde a domiciliação inicial implicou a participação dessa espécie e do Triatoma infestans. Após a realização do expurgo, as pesquisas de vigilância com ritmo trimestral e o levantamento final evidenciaram a ocorrência de novo processo de domiciliação triatomínea, porém restrita ao P. megistus e limitada ao peridomicílio, com coeficientes de positividade de edifícios acentuadamente inferiores aos registrados quando do levantamento inicial. Tal situação perdurou durante todo o período de observação. Após o expurgo, o valor geral do coeficiente de positividade dos edifícios variou do valor mínimo de 0,8% ao máximo de 2,7%, enquanto que foi de 23,4% o observado por ocasião do primeiro levantamento. Essa situação persistiu pelo tempo mínimo de dois anos e quatro meses, o que permite recomendar que a vigilância e a aplicação do expurgo seletivo, se necessário, sejam iniciadas após cerca de três anos decorridos da desinsetização geral. Recomenda-se que, nesse interim, se proceda à motivação dos habitantes locais objetivando obter-lhes a colaboração para a denúncia de novos focos intradomiciliares. No possível mecanismo de transferência da infecção tripanossômica para o ambiente domiciliar, as evidências sugerem a participação de vertebrados domiciliados, em especial modo ratos (Rattus) e gambás (Didelphis), de hábitos ubiquistas. O papel do P. megistus no processo de evolução da nova domiciliação triatomínea foi praticamente exclusivo, tendo o Rhodnius neglectus ocorrido de maneira esporádica. O não reaparecimento do T. infestans pôde ser atribuído à pouca ou mesmo ausente mobilidade da população humana local. Os resultados da participação de P. megistus na reinfestação domiciliar mostrou que esta rapidamente atingiu os níveis de positividade observados para essa espécie na área testemunha, mas sem tendência ao incremento posterior.