Lessons from a national survey of Chagas disease transmission risk in Colombia

Chagas disease control-surveillance in the Americas: the multinational initiatives and the practical impossibility of interrupting vector-borne Trypanosoma cruzi transmission

Chagas disease (CD) still imposes a heavy burden on most Latin American countries. Vector-borne and mother-to-child transmission cause several thousand new infections per year, and at least 5 million people carry Trypanosoma cruzi. Access to diagnosis and medical care, however, is far from universal. Starting in the 1990s, CD-endemic countries and the Pan American Health Organization-World Health Organization (PAHO-WHO) launched a series of multinational initiatives for CD control-surveillance. An overview of the initiatives’ aims, achievements, and challenges reveals some key common themes that we discuss here in the context of the WHO 2030 goals for CD. Transmission of T. cruzi via blood transfusion and organ transplantation is effectively under control. T. cruzi, however, is a zoonotic pathogen with 100+ vector species widely spread across the Americas; interrupting vector-borne transmission seems therefore unfeasible. Stronger surveillance systems are, and will continue to be, needed to monitor and control CD. Prevention of vertical transmission demands boosting current efforts to screen pregnant and childbearing-aged women. Finally, integral patient care is a critical unmet need in most countries. The decades-long experience of the initiatives, in sum, hints at the practical impossibility of interrupting vector-borne T. cruzi transmission in the Americas. The concept of disease control seems to provide a more realistic description of what can in effect be achieved by 2030.

Distribution and natural infection status of synantrophic triatomines (Hemiptera: Reduviidae), vectors of Trypanosoma cruzi, reveals new epidemiological scenarios for chagas disease in the Highlands of Colombia

INTRODUCTION

Updating the distribution and natural infection status of triatomine bugs is critical for planning, prioritizing, and implementing strategies to control Chagas disease (CD), especially after vector reduction programs. After carrying out a control program, the Department of Boyaca contains the highest number of Colombian municipalities certified by PAHO to be free of intradomiciliary transmission of Trypanosoma cruzi by Rhodnius prolixus. The present work describes the spatial distribution, natural infection (NI), and molecular characterization of T. cruzi in synanthropic triatomines from the Department of Boyaca in 2017 and 2018.

MATERIALS AND METHODS

An entomological survey was conducted in 52 municipalities in Boyaca known to have had previous infestations of triatomine bugs. Insects were collected through active searches carried out by technical personnel from the Secretary of Health and community members using Triatomine Collection Stations (PITs-acronym in Spanish). For evaluation of natural infection, triatomines were identified morphologically and grouped in pools of one to five individuals of the same species collected in the same household. DNA derived from the feces of each pool of insects was analyzed by PCR for the presence of T. cruzi using primers flanking the satellite DNA of the parasite. SL-IR primers were used to differentiate TCI from the other DTUs and to identify different genotypes. The distribution of the collected triatomines was analyzed to determine any vector hotspots using spatial recreation.

RESULTS

A total of 670 triatomine bugs was collected, belonging to five species: Triatoma dimidiata (73.2%), Triatoma venosa (16.7%), Panstrongylus geniculatus (5.7%), Rhodnius prolixus (4.4%), and Panstrongylus rufotuberculatus (0.4%), from 29 of the 52 municipalities. In total, 71.6% of the bugs were collected within houses (intradomiciliary) and the rest around the houses (peridomiciliary). Triatoma dimidiata was the most widely distributed species and had the highest natural infection index (37.8%), followed by T. venosa and P. geniculatus. TcI was the only DTU found, with the TcI Dom genotype identified in 80% of positive samples and TcI sylvatic in the other insects. Spatial analysis showed clusters of T. dimidiata and T. venosa in the northeast and southwest regions of Boyaca.

CONCLUSIONS

After some municipalities were certified free of natural transmission within houses (intradomiciliary transmission) of T. cruzi by R. prolixus, T. dimidiata has become the most prevalent vector present, and represents a significant risk of resurgent CD transmission. However, T. venosa, P. geniculatus, and P. rufotuberculatus also contribute to the increased risk of transmission. The presence of residual R. prolixus may undo the successes achieved through vector elimination programs. The molecular and spatial analysis used here allows us to identify areas with an ongoing threat of parasite transmission and improve entomological surveillance strategies.

Chagas disease-related mortality in Colombia from 1979 to 2018: temporal and spatial trends

INTRODUCTIOn:

Studies on Chagas disease-related mortality assist in decision-making in health policies. We analyzed the epidemiological characteristics, temporal trends, and regional differences in Chagas disease-related mortality in Colombia from 1979 to 2018.

METHODS:

A time-series study was conducted using death records and population data from the National Administrative Department of Statistics, using categorizations from the International Classification of Disease (ICD)-9 and ICD-10 systems. All deaths with Chagas disease as an underlying or associated cause of death were included. Crude and age-sex standardized mortality rates per 100,000 inhabitants and the annual percent change (APC) were calculated.

RESULTS:

Of the 7,287,461 deaths recorded in Colombia during 1979-2018, 3,276 (0.04%) deaths were related to Chagas disease-2,827 (86.3%) as an underlying cause and 449 (13.7%) as an associated cause. The average annual age-sex standardized mortality rate was 0.211 (95% confidence interval [CI]: 0.170-0.252) deaths/100,000 inhabitants, with a significant upward trend (APC = 6.60%; 95% CI: 5.9-7.3). The highest Chagas disease-related death rates were in males (0.284 deaths/100,000 inhabitants), those ≥65 years old (1.296 deaths/100,000 inhabitants), and residents of the Orinoco region (1.809 deaths/100,000 inhabitants). There was a significant increase in mortality in the Orinoco (APC = 8.28%; 95% CI: 6.4-10.2), Caribbean (APC = 5.06%; 95% CI: 3.6-6.5), and Andean (APC = 4.63%; 95% CI: 3.9-5.3) regions.

CONCLUSIONS:

Chagas disease remains a major public health issue in Colombia with high mortality rates in older age groups, a wide geographic distribution, regional differences, and the potential to increase.

Eco-epidemiological study reveals the importance of Triatoma dimidiata in the Trypanosoma cruzi transmission, in a municipality certified without transmission by Rhodnius prolixus in Colombia

Boyaca department is an endemic area for Chagas disease in Colombia, where 24 of its municipalities have been certified by the PAHO with interruption of Trypanosoma cruzi transmission by R. prolixus. However, the presence of secondary vectors, represent a risk of parasite transmission for citizens and a challenge for the health care institutions. The aim of this work was to investigate eco-epidemiological features of Chagas disease in the municipality of Socota (Boyaca), in order to improve control and surveillance strategies. To understand the transmission dynamics of T. cruzi in this area, we designed a comprehensive, multi-faceted study including: (i) entomological survey in five villages (La Vega, Comaita, Chusvita, Guaquira and Pueblo Nuevo), (ii) blood meal source determination, (iii) T. cruzi infection rate in collected triatomines, (iv) identification of circulating T. cruzi genotypes, (v) serological determination of T. cruzi infection in domestic dogs; and (vi) evaluation of infection in synanthropic mammals. A total of 90 T. dimidiata were collected, of which 73.3% (66/90) and 24.4% (22/90) were collected inside dwellings and peridomestic areas, respectively, while the rest (2/90) in Chusvita Elementary School. T. cruzi infection was evidenced in 40% (36/90) of triatomine bugs using PCR analyses, in which only DTU I was found, and TcI _Dom was the most distributed. Blood-meal analysis showed that T. dimidiata only fed of humans. Seroprevalence in domestic dogs was 4.6% (3/66), while that two Didelphis marsupialis captured showed no infection. In conclusion, the high dispersion and colonization of T. dimidiata shown in this municipality, along the high rate of T. cruzi (TcI) infection and its anthropophilic behavior constitute a risk situation for Chagas disease transmission in this municipality certified without R. prolixus. The epidemiological implications of these findings are herein discussed.

Funding for Chagas Disease: A 10-Year (2009-2018) Survey

Chagas disease was discovered in 1909 by the Brazilian scientist Carlos Chagas. After more than 110 years, many outcomes have been achieved in all research fields; however, Chagas disease remains a serious public health problem, mainly in Latin America, being one of the most neglected tropical diseases in the world. As a neglected disease, it receives very little financial support. Nevertheless, how much is actually spent? With this question in mind, the goal of the present work was to summarize all funding employed by multiple institutions in the Chagas disease field in a 10-year survey. From 2009 to 2018, Chagas disease received only USD 236.31 million, representing 0.67% of the total applied for all neglected diseases in this period. Mostly, the investments are concentrated in basic research (47%) and drug development (42.5%), with the public sector responsible for 74% of all funding, followed by the industry (19%) and philanthropy (7%). Relevantly, NIH (USA) alone accounted for more than half of the total investment. Taking into account that Chagas disease has a great socio-economic impact, it is clear that more investments are needed, especially from endemic countries. Furthermore, coordinated strategies to make better use of resources and incentives for the pharmaceutical industry must be adopted.

Genetic diversification of Panstrongylus geniculatus (Reduviidae: Triatominae) in northern South America

Triatomines are the vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. Although Triatoma and Rhodnius are the most-studied vector genera, other triatomines, such as Panstrongylus, also transmit T. cruzi, creating new epidemiological scenarios. Panstrongylus has at least 13 reported species but there is limited information about its intraspecific genetic variation and patterns of diversification. Here, we begin to fill this gap by studying populations of P. geniculatus from Colombia and Venezuela and including other epidemiologically important species from the region. We examined the pattern of diversification of P. geniculatus in Colombia using mitochondrial and nuclear ribosomal data. Genetic diversity and differentiation were calculated within and among populations of P. geniculatus. Moreover, we constructed maximum likelihood and Bayesian inference phylogenies and haplotype networks using P. geniculatus and other species from the genus (P. megistus, P. lignarius, P. lutzi, P. tupynambai, P. chinai, P. rufotuberculatus and P. howardi). Using a coalescence framework, we also dated the P. geniculatus lineages. The total evidence tree showed that P. geniculatus is a monophyletic species, with four clades that are concordant with its geographic distribution and are partly explained by the Andes orogeny. However, other factors, including anthropogenic and eco-epidemiological effects must be investigated to explain the existence of recent geographic P. geniculatus lineages. The epidemiological dynamics in structured vector populations, such as those found here, warrant further investigation. Extending our knowledge of P. geniculatus is necessary for the accurate development of effective strategies for the control of Chagas disease vectors.

Prevalence of Trypanosoma cruzi infection in active military population of The Colombian National Army gathered in five departments

Background

The National Army of Colombia is present in all of the national territory, focused in sylvatic zones where they are exposed continually to potential risk of transmission of Trypanosoma cruzi, the etiological agent of the Chagas disease. People of this study were active personal that were born and lived during their first years in endemic areas of transmission through domiciled vectors as Rhodnius prolixus.

Aim

The main aim of this study was to estimate the prevalence of Chagas disease in the active military population of the National Army, gathered in five departments.

Methods

An observational and descriptive study with cross-sectional analysis was carried out. Blood sample each patient in order to apply serological diagnosis by two different Enzyme Linked ImmunoSorbent Assay tests, following the algorithm of National Institute of Health, Colombia. In cases of serum results with inconsistencies, a Hemagglutination Inhibition test and Indirect Immunofluorescence assay test were performed to solve inconclusiveness. Positive samples by two different tests were considered seropositive. Additionally, to each positive sample by at least one serological test, we did extraction of DNA for molecular diagnosis.

Results

295 serums were analyzed and two of them were positive in order to get a prevalence of 0.68%. Two samples analyzed by molecular diagnosis were negative.

Conclusion

The prevalence was < 1% It is probable the infection in the seropositive individuals occurred before enlisting in the military service due to origin locations with transmission such as Casanare and Boyacá. These findings allow defining the prevention and control programs of chronic cases and reduction in the disease burden.

Heterogeneity of Trypanosoma cruzi infection rates in vectors and animal reservoirs in Colombia: a systematic review and meta-analysis

Background

The heterogeneity of Trypanosoma cruzi infection rates among triatomines insects and animal reservoirs has been studied in independent studies, but little information has been systematised to allow pooled and comparative estimates. Unravelling the main patterns of this heterogeneity could contribute to a further understanding of T. cruzi transmission in Colombia.

Methods

A systematic search was conducted in PubMed, Medline, LILACS, Embase, Web of Knowledge, Google Scholar and secondary sources with no filters of language or time and until April 2018. Based on selection criteria, all relevant studies reporting T. cruzi infection rates in reservoirs or triatomines were chosen. For pooled analyses, a random effects model for binomial distribution was used. Heterogeneity among studies is reported as I². Subgroup analyses included: taxonomic classification, ecotope and diagnostic methods. Publication bias and sensitivity analyses were performed.

Results

Overall, 39 studies reporting infection rates in Colombia were found (22 for potential reservoirs and 28 for triatomine insects) for a total sample of 22,838 potential animals and 11,307 triatomines evaluated for T. cruzi infection. We have found evidence of 38/71 different animal species as potential T. cruzi reservoirs and 14/18 species as triatomine vectors for T. cruzi. Among animals, the species with the highest pooled prevalence were opossum (Didelphis marsupialis) with 48.0% (95% CI: 26–71%; I² = 88%, τ² = 0.07, P < 0.01) and domestic dog (Canis lupus familiaris) with 22.0% (95% CI: 4–48%; I² = 96%, τ² = 0.01, P < 0.01). Among triatomines, the highest prevalence was found for Triatoma maculata in the peridomestic ecotope (68.0%, 95% CI: 62–74%; I² = 0%, τ² = 0, P < 0.0001), followed by Rhodnius prolixus (62.0%, 95% CI: 38–84%; I² = 95%, τ² = 0.05, P < 0.01) and Rhodnius pallescens (54.0%, 95% CI: 37–71%; I² = 86%, τ² = 0.035, P < 0.01) in the sylvatic ecotope.

Conclusions

To our knowledge, this is the first systematic and quantitative analyses of triatomine insects and potential animal reservoirs for T. cruzi infection in Colombia. The results highlight a marked heterogeneity between species and provide initial estimates of infection rates heterogeneity.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3541-5) contains supplementary material, which is available to authorized users.

Prevalence of Chagas disease in Colombia: A systematic review and meta-analysis

Background

Despite the adoption of campaigns to interrupt the main vector and to detect Trypanosoma cruzi in blood banks, millions of people are still chronically infected; however, the prevalence data are limited, and the epidemiology of Chagas disease has not been systematically evaluated. This study aimed to estimate the prevalence of Chagas disease in Colombia.

Methods

A systematic literature review and meta-analysis was conducted to select all observational studies reporting the prevalence of Chagas disease in Colombia, based on serological diagnosis in participants of any age and published between January 2007 and November 2017. Pooled estimates and 95% confidence intervals (95% CIs) were calculated using random-effects models. In addition, the I² statistic was calculated.

Results

The literature search yielded a total of 1,510 studies; sixteen articles with relevant prevalence data were included in the systematic review. Of these, only 12 articles were included for entry in the meta-analysis. The pooled prevalence of Chagas disease across studies was 2.0% (95% CI: 1.0–4.0). A high degree of heterogeneity was found among studies (I² > 75%; p < 0.001). The publication bias was not statistically significant (Egger’s test, p = 0.078). The highest pooled prevalences were found in the adult population (3.0%, 95% CI: 1.0–4.0), pregnant women (3.0%, 95% CI: 3.0–4.0) and the Orinoco region (7.0%, 95% CI: 2.2–12.6).

Conclusions

The results indicate that the T. cruzi-infected population is aging, the adult population, pregnant women and that the Orinoco region (department of Casanare) have the highest prevalences. These results highlight the need to maintain screening and surveillance programs to identify people with chronic T. cruzi infections.

Trypanosoma cruzi Detection in Colombian Patients with a Diagnosis of Esophageal Achalasia

Achalasia is a motility disorder of the esophagus that might be secondary to a chronic Trypanosoma cruzi infection. Several studies have investigated esophageal achalasia in patients with Chagas disease (CD) in Latin America, but no related studies have been performed in Colombia. The goals of the present study were to determine the presence of anti-T. cruzi antibodies in patients with esophageal achalasia who visited a referral hospital in Bogotá, Colombia, and to detect the presence of the parasite and its discrete typing units (DTUs). This cross-sectional study was conducted in adult patients (18-65 years old) who were previously diagnosed with esophageal achalasia and from whom blood was drawn to assess antibodies against T. cruzi using four different serological tests. Trypanosoma cruzi DNA was detected by conventional polymerase chain reaction (cPCR) and quantitative polymerase chain reaction (qPCR). In total, 38 patients, with an average age of 46.6 years (standard deviation of ±16.2) and comprising 16 men and 22 women, were enrolled. Five (13.15%) patients were found to be positive for anti-T. cruzi antibodies by indirect immunofluorescence assay (IFA), and two patients who were negative according to IFA were reactive by both enzyme-linked immunosorbent assay and immunoblot (5.3%). Parasite DNA was detected in two of these seven patients by cPCR and in one of these by qPCR. The parasite DTU obtained was TcI. In summary, this study identified T. cruzi in Colombian patients with esophageal achalasia, indicating that digestive compromise could also be present in patients with chronic CD.

Multi-criteria decision analysis and spatial statistic: an approach to determining human vulnerability to vector transmission of Trypanosoma cruzi

BACKGROUND

Chagas disease (CD), caused by the protozoan Trypanosoma cruzi, is a neglected human disease. It is endemic to the Americas and is estimated to have an economic impact, including lost productivity and disability, of 7 billion dollars per year on average.

OBJECTIVES

To assess vulnerability to vector-borne transmission of T. cruzi in domiciliary environments within an area undergoing domiciliary vector interruption of T. cruzi in Colombia.

METHODS

Multi-criteria decision analysis [preference ranking method for enrichment evaluation (PROMETHEE) and geometrical analysis for interactive assistance (GAIA) methods] and spatial statistics were performed on data from a socio-environmental questionnaire and an entomological survey. In the construction of multi-criteria descriptors, decision-making processes and indicators of five determinants of the CD vector pathway were summarily defined, including: (1) house indicator (HI); (2) triatominae indicator (TI); (3) host/reservoir indicator (Ho/RoI); (4) ecotope indicator (EI); and (5) socio-cultural indicator (S-CI).

FINDINGS

Determination of vulnerability to CD is mostly influenced by TI, with 44.96% of the total weight in the model, while the lowest contribution was from S-CI, with 7.15%. The five indicators comprise 17 indices, and include 78 of the original 104 priority criteria and variables. The PROMETHEE and GAIA methods proved very efficient for prioritisation and quantitative categorisation of socio-environmental determinants and for better determining which criteria should be considered for interrupting the man-T. cruzi-vector relationship in endemic areas of the Americas. Through the analysis of spatial autocorrelation it is clear that there is a spatial dependence in establishing categories of vulnerability, therefore, the effect of neighbors’ setting (border areas) on local values should be incorporated into disease management for establishing programs of surveillance and control of CD via vector.

CONCLUSIONS

The study model proposed here is flexible and can be adapted to various eco-epidemiological profiles and is suitable for focusing anti-T. cruzi serological surveillance programs in vulnerable human populations.

New Scenarios of Chagas Disease Transmission in Northern Colombia

Chagas disease (CD) is a systemic parasitic infection caused by the flagellated form of Trypanosoma cruzi. Córdoba department, located in the Colombian Caribbean Coast, was not considered as a region at risk of T. cruzi transmission. In this article, we describe the first acute CD case in Salitral village in Sahagún, Córdoba, confirmed by microscopy and serological tests. Our results draw attention to a new scenario of transmission of acute CD in nonendemic areas of Colombia and highlight the need to include CD in the differential diagnosis of febrile syndromes in this region.

Genetic Relationships and Spatial Genetic Structure Among Populations of Rhodnius prolixus (Hemiptera: Reduviidae) in Colombia and Venezuela Based on Mitochondrial Cytochrome-b Sequences

One hundred twenty Rhodnius prolixus (Stal) (Hemiptera: Reduviidae) specimens from 6 Colombian Departments and 1 Venezuelan State had 594-bp of the mitochondrial cytochrome-b gene sequenced to improve the understanding of evolutionary processes that shape the main vector of Chagas disease. The levels of genetic diversity for this species were low-medium with reference to other bugs. The genetic heterogeneity among the populations was very limited which means there has been extensive gene flow and/or very recent split processes. The overall sample as well as some individual populations showed evidence of recent population expansions (with the exception of Arauca, which yielded evidence of a bottleneck for a mismatch distribution). This expansion (11,000 or 2000-25,000 year ago depending of two procedures employed) coincides with the ending of the last intense glacial conditions during the Pleistocene and the beginning of the Holocene that had a warmer and wetter climate. Some of our autocorrelation analyses (AIDA and Genetic Landscape Interpolation Analysis) indicated local patches of high genetic similarity but no globally significant spatial structure. We did show an original haplotype distributed throughout the entirety of the geographical area studied.

Transmission scenarios of major vector-borne diseases in Colombia, 1990-2016

Introducción. Las enfermedades transmitidas por vectores representan más de 17 % de todas las enfermedades infecciosas y causan anualmente un millón de defunciones a nivel mundial. En Colombia, la malaria, el dengue, la enfermedad de Chagas y las leishmaniasis son condiciones endemoepidémicas persistentes.Objetivo. Determinar el comportamiento epidemiológico de las enfermedades transmitidas por vectores en zonas urbanas y rurales de Colombia entre 1990 y 2016.Materiales y métodos. Se hizo un estudio descriptivo del comportamiento epidemiológico de las principales enfermedades transmitidas por vectores en zonas urbanas y rurales de Colombia entre 1990 y 2016, con la información proveniente de fuentes oficiales secundarias.Resultados. En el periodo estudiado se registraron 5'360.134 casos de enfermedades transmitidas por vectores, de los cuales 54,7 % fueron de malaria y 24,9 % de dengue. Estos casos concentraron el 80 % de la carga acumulada de casos de enfermedades transmitidas por vectores. Las medianas de las tasas de incidencia fueron 1.371 y 188 por 100.00 habitantes para malaria y dengue, respectivamente. Además, los casos de chikungunya fueron 774.831 desde su introducción en el 2014 y, los de Zika, 117.674 desde su aparición en 2015. En las zonas rurales predominaron las enfermedades parasitarias transmitidas por vectores como la malaria, las leishmaniasis y la enfermedad de Chagas. A nivel urbano, predominaron el dengue, el chikungunya y el Zika.Conclusiones. La transmisión en Colombia de estas enfermedades es persistente en las zonas urbanas y en las rurales, y de tipo endemoepidémico en los casos de malaria, dengue, leishmaniasis y enfermedad de Chagas. Dicha transmisión se ha dado de manera focalizada y con patrones variables de intensidad. Asimismo, se mantienen las condiciones que han favorecido la transmisión emergente de nuevas arbovirosis.

Prevalence of anti-Trypanosoma cruzi antibodies in women of childbearing age in Socotá, Boyacá, 2014

INTRODUCTION

Chagas' disease is a parasitic disease caused by the protozoan Trypanosoma cruzi. This condition presents epidemiological risk factors associated with socioeconomic conditions and is currently considered an important public health problem. Its presence has been reported in endemic regions at elevations of up to 2,000 meters above sea level. 

OBJECTIVE

To determine the prevalence of anti-T. cruzi antibodies and the possible risk factors associated with this condition in women of childbearing age from the town of Socotá, Boyacá. 

MATERIALS AND METHODS

An observational, descriptive cross-sectional study was conducted in a population of women of childbearing age from Socotá, Boyacá. The samples were analyzed by Chagas ELISA IgG and IgM test and indirect hemagglutination test. A univariate analysis and statistical association of variables were performed. 

RESULTS

A confirmed prevalence of 2/138 (1.4%) was found in this town. Having pets or a history of contact with vectors were possible associated risk factors although without statistical significance. 

CONCLUSIONS

From the results obtained in the present study, it is suggested that more active research be carried out for cases of Chagas' disease in non-endemic areas in Colombia that present risk factors for acquiring the disease, even when the environmental conditions and elevation differ from those described in the literature.

Geographic Distribution and Ecology of Triatoma dimidiata (Hemiptera: Reduviidae) in Colombia

Triatoma dimidiata Latreille is the second most important vector of Chagas' disease in Colombia and is found in urban and periurban areas. From January 2007 to June 2008, we performed field work in 8 departments, 18 municipalities, and 44 rural villages, covering most of its known distribution and all of its ecological zones in the country. The goal was to determine the geographical distribution, the ecology, and house infestation indices of T. dimidiata over its range and hence the Chagas' disease transmission risk. In Colombia, T. dimidiata occupies a wide variety of ecosystems, from transformed ecosystems in the Andean biome with shrub and xerofitic vegetation to very dense forests in the humid tropical forests in the Sierra Nevada of Santa Marta. According to genetic and ecological criteria, at least two T. dimidiata forms of this species are present: populations from the northwest of the country (Caribbean plains) are restricted to palm tree habitats, and domestic involvement is limited to sporadic visits because of attraction by light; and populations of the east region (Andean mountains) presenting a complex distributional pattern including sylvatic, peridomestic, and domiciliated ecotopes, and occupying a great variety of life zones. The latter population is of epidemiological importance due to the demonstrated migration and genetical flow of individuals among the different habitats. Control, therefore, must take into account its diversity of habitats.

Risk factors associated with Chagas disease in pregnant women in Santander, a highly endemic Colombian area

OBJECTIVE

To determine the prevalence and risk factors associated with Chagas disease in pregnant women in an endemic area of Santander, Colombia.

METHODS

Cross-sectional study included 23 municipalities of Santander, Colombia. Serological IFAT and ELISA tests were undertaken to detect IgG anti- Trypanosoma cruzi. A questionnaire was conducted for assessing the risk factors of each participant. Newborns were evaluated at birth and followed up to 1 year of age to determine congenital infection.

RESULTS

An overall prevalence of 3.2% (95% CI 2.4-4.2) among 1518 pregnant women was detected. Prevalences by provinces were as follows: Guanentina: 6.0% (95% CI 4.1-8.5), García Rovira: 2.9% (95% CI: 1.5-4.8) and Comunera: 0.4% (0.4-2.3). The main risk factors identified were age >32 years old (OR: 2.1; 95% CI: 1.1-3.9); currently having a thatched roof (OR: 11.8; CI95% 2.2-63.2) and a thatched roof during childhood (OR: 3.0; 95% CI: 1.4-6.6); having below primary school education level (OR: 4.6; 95% CI: 2.2-9.5); and a history of a close contact with the vector (triatomine bugs) at least once during their lifetime (OR: 6.9; 95% CI: 3.7-12.9). No congenital cases were detected by parasitological or serological techniques.

CONCLUSIONS

Prevalence of Chagas disease in pregnant women is a potential source of infection in this Colombian endemic area. The main risk factors associated with seropositivity were related to conditions favouring the contact with the vector. The results show that it is necessary to continue an active surveillance in order to offer diagnosis and treatment to mothers and their newborns in addition to screening to pregnant women from endemic areas.

Acute Chagas outbreaks: molecular and biological features of Trypanosoma cruzi isolates, and clinical aspects of acute cases in Santander, Colombia

BACKGROUND

Outbreaks of acute Chagas disease associated with oral transmission are easily detected nowadays with trained health personnel in areas of low endemicity, or in which the vector transmission has been interrupted. Given the biological and genetic diversity of Trypanosoma cruzi, the high morbidity, mortality, and the observed therapeutic failure, new characteristics of these outbreaks need to be addressed at different levels, both in Trypanosoma cruzi as in patient response. The aim of this work was to evaluate the patient's features involved in six outbreaks of acute Chagas disease which occurred in Santander, Colombia, and the characteristics of Trypanosoma cruzi clones isolated from these patients, to establish the potential relationship between the etiologic agent features with host behavior.

METHODS

The clinical, pathological and epidemiological aspects of outbreaks were analyzed. In addition, Trypanosoma cruzi clones were biologically characterized both in vitro and in vivo, and the susceptibility to the classical trypanocidal drugs nifurtimox and benznidazole was evaluated. Trypanosoma cruzi clones were genotyped by means of mini-exon intergenic spacer and cytochrome b genes sequencing.

RESULTS

All clones were DTU I, and based on the mini-exon intergenic spacer, belong to two genotypes: G2 related with sub-urban, and G11 with rural outbreaks. Girón outbreak clones with higher susceptibility to drugs presented G2 genotype and C/T transition in Cyt b. The outbreaks affected mainly young population (±25.9 years), and the mortality rate was 10 %. The cardiac tissue showed intense inflammatory infiltrate, myocardial necrosis and abundant amastigote nests. However, although the gastrointestinal tissue was congestive, no inflammation or parasites were observed.

CONCLUSIONS

Although all clones belong to DTU I, two intra-DTU genotypes were found with the sequencing of the mini-exon intergenic spacer, however there is no strict correlation between genetic groups, the cycles of the parasite or the clinical forms of the disease. Trypanosoma cruzi clones from Girón with higher sensitivity to nifurtimox presented a particular G2 genotype and C/T transition in Cyt b. When the diagnosis was early, the patients responded well to antichagasic treatment, which highlights the importance of diagnosis and treatment early to prevent fatal outcomes associated with these acute episodes.

Ten years (2004-2014) of Chagas disease surveillance and vector control in Ecuador: successes and challenges

OBJECTIVE

To describe the current situation of Chagas disease in Ecuador and to evaluate the impact of vector control for the period 2004-2014.

METHODS

Since 2004, the Ministry of Public Health has formalized activities for the surveillance and control of Chagas disease and we analyzed here available records.

RESULTS

More than 200 000 houses were surveyed, and 2.6% were found to be infested (95% CI: 2.6-2.7), and more than 51 000 houses were sprayed with residual insecticide, with important yearly variations. A total of 915 cases of T. cruzi infection were registered. The Amazon region is emerging as a high priority area, where nearly half of T. cruzi infection cases originate. The costal region and the southern highland valleys remain important high-risk area. Vector control efforts over the past 10 years have been effective in the coastal region, where T. dimidiata predominates, and resulted in important reductions in house infestation indices in many areas, even reaching negligible levels in some parishes.

CONCLUSION

Vector efforts need to be sustained and expanded for the elimination of T. dimidiata to be feasible. Novel vector control interventions need to be designed to reduce intrusion by several triatomine species present in the Amazon region and southern Ecuador. Strong political commitment is needed to sustain current achievements and improve the national coverage of these programmes.

The impact of landscape transformation on the reinfestation rates of Rhodnius prolixus in the Orinoco Region, Colombia

Trypanosoma cruzi, the agent responsible for Chagas disease, is widely distributed in the Americas in association to insect vectors and animal reservoirs. Triatomines are common vectors of Chagas disease and they vary in their distribution and affinity to human or sylvatic environments. Thus, control programs that include house spraying have been successful in regions were insects have a tendency to domiciliation. In the Orinoco region of Colombia, Rhodnius prolixus is the main vector presenting a stable sylvatic cycle, but is also found colonizing human dwellings. In 1997, health authorities developed a control program in the Department of Casanare spreading with insecticide houses in 667 localities. Infestation Indexes (I.I.) were calculated at the locality level before and after spraying. Times for re-infestation assessment varied between 1 and 67 months. Localities were classified into 3 groups according to their I.I. after spraying. Group 1 dropped their I.I. down to zero, Group 2 had a drop but remained positive and Group 3 increased its I.I. after spraying. We classified each group in terms of their land use characteristics before and after spraying based on satellite images obtained for the years 1997 (beginning of the study) and 2002 (end of program). We found that spraying significantly reduce the I.I. on average. However, we found that time after spraying does not produce significant differences in the I.I. Interestingly, land use changes and variations on I.I. after spraying for all groups were significantly dependent.

The potential of canine sentinels for reemerging Trypanosoma cruzi transmission

BACKGROUND

Chagas disease, a vector-borne disease transmitted by triatomine bugs and caused by the parasite Trypanosoma cruzi, affects millions of people in the Americas. In Arequipa, Peru, indoor residual insecticide spraying campaigns are routinely conducted to eliminate Triatoma infestans, the only vector in this area. Following insecticide spraying, there is risk of vector return and reinitiation of parasite transmission. Dogs are important reservoirs of T. cruzi and may play a role in reinitiating transmission in previously sprayed areas. Dogs may also serve as indicators of reemerging transmission.

METHODS

We conducted a cross-sectional serological screening to detect T. cruzi antibodies in dogs, in conjunction with an entomological vector collection survey at the household level, in a disease endemic area that had been treated with insecticide 13 years prior. Spatial clustering of infected animals and vectors was assessed using Ripley's K statistic, and the odds of being seropositive for dogs proximate to infected colonies was estimated with multivariate logistic regression.

RESULTS

There were 106 triatomine-infested houses (41.1%), and 45 houses infested with T. cruzi-infected triatomine insects (17.4%). Canine seroprevalence in the area was 12.3% (n=154); all seropositive dogs were 9 months old or older. We observed clustering of vectors carrying the parasite, but no clustering of seropositive dogs. The age- and sex-adjusted odds ratio between seropositivity to T. cruzi and proximity to an infected triatomine (≤50m) was 5.67 (95% CI: 1.12-28.74; p=0.036).

CONCLUSIONS

Targeted control of reemerging transmission can be achieved by improved understanding of T. cruzi in canine populations. Our results suggest that dogs may be useful sentinels to detect re-initiation of transmission following insecticide treatment. Integration of canine T. cruzi blood sampling into existing interventions for zoonotic disease control (e.g., rabies vaccination programs) can be an effective method of increasing surveillance and improving understanding of disease distribution.

New scenarios of Trypanosoma cruzi transmission in the Orinoco region of Colombia

Rhodnius prolixus, a blood-sucking triatomine with domiciliary anthropophilic habits, is the main vector of Chagas disease. The current paradigm of Trypanosoma cruzi transmission in Columbia includes a sylvatic and domiciliary cycle co-existing with domestic and sylvatic populations of reservoirs. The aim of this study is to evaluate the population densities and relative abundance of triatomines and mammals that may be involved in the sylvatic cycle of Chagas disease to clarify the epidemiological scenario in an endemic area in the province of Casanare. Insect vectors on Attalea butyracea palms were captured using both manual searches and bait traps. The capture of mammals was performed using Sherman and Tomahawk traps. We report an infestation index of 88.5% in 148 palms and an index of T. cruzi natural infection of 60.2% in 269 dissected insects and 11.9% in 160 captured mammals. High population densities of triatomines were observed in the sylvatic environment and there was a high relative abundance of reservoirs in the area, suggesting a stable enzootic cycle. We found no evidence of insect domiciliation. Taken together, these observations suggest that eco-epidemiological factors shape the transmission dynamics of T. cruzi, creating diverse scenarios of disease transmission.

Ecology, evolution and control of Chagas disease: a century of neglected modelling and a promising future

More than 100 years after its formal description, Chagas disease remains a major public health concern in Latin America with a yearly burden of 430,000 Disability-Adjusted Life Years (DALYs). The aetiological agent, a protozoan named Trypanosoma cruzi, is mainly transmitted to mammalian hosts by triatomine vectors. Multiple species of mammals and triatomines can harbour and transmit the parasite, and the feeding range of triatomine species typically includes many noncompetent hosts. Furthermore, the transmission of the pathogen can occur via several routes including the typical vector's faeces, but also oral, congenital and blood transfusion routes. These ecological and epidemiological complexities of the disease have hindered many control initiatives. In such a context, mathematical models provide invaluable tools to explore and understand the dynamics of T. cruzi transmission, and to design, optimize and monitor the efficacy of control interventions. We intend here to provide the first review of the mathematical models of Chagas disease, focussing on how they have contributed to our understanding of (1) the population dynamics and control of triatomine vectors, and (2) the epidemiology of T. cruzi infections. We also aim at suggesting promising lines of modelling that could further improve our understanding of the ecology, evolution, and control of the disease.

Environmental changes can produce shifts in chagas disease infection risk

An epidemiological network contains all the organisms involved (types) in the transmission of a parasite. The nodes of the network represent reservoirs, hosts, and vectors, while the links between the nodes represent the strength and direction of parasite movement. Networks that contain humans are of special interest because they are of concern to public health authorities. Under these circumstances, it is possible, in principle, to identify cycles (closed paths in the network) that include humans and select the ones that carry the maximum probability of human infection. The basic reproduction number R 0 in such a network gives the average number of new infections of any type after the introduction of one individual infected by any type. To obtain R 0 for complex networks, one can use the next-generation matrix (NGM) approach. Every entry in NGM will average the contribution of each link that connects two types. To tease the contribution of every cycle apart, we define the virulence as the geometric mean of the NGM entries corresponding to the links therein. This approach allows for the quantification of specific cycles of interest while it also makes the computation of the sensitivity and elasticity of the parameters easier. In this work, we compute the virulence for the transmission dynamics of Chagas disease for a typical rural area in Colombia incorporating the effect of environmental changes on the vector population size. We concluded that the highest contribution to human infection comes from humans themselves, which is a surprising and interesting result. In addition, sensitivity analysis revealed that increasing vector population size increases the risk of human infection.

[Investigation of vectors and reservoirs in an acute Chagas outbreak due to possible oral transmission in Aguachica, Cesar, Colombia]

Colombia recorded 11 cases of acute Chagas disease and 80 cases of oral contamination with Trypanosoma cruzi. The current study analyzes the entomological and parasitological characteristics of the outbreak in Aguachica, Cesar Department, in 2010. An interdisciplinary group of health professionals and regional university personnel conducted the laboratory tests in the patients and the investigation of the transmission focus. Eleven cases of acute Chagas diseases were detected in a single family in a dwelling with domiciliated triatomines and Rhodnius pallescens, Pantrongylus geniculatus, Eratyrus cuspidatus, and two Didelphis marsupialis opossums infected with T. cruzi in Attalea butyracea and Elaeis oleifera palm trees in the urban area of Aguachica. The study analyzes the role of R. pallescens and palm trees in the wild cycle of T. cruzi and in oral transmission of Chagas disease. Sporadic incursions by wild R. pallescens, P. geniculatus, and E. cuspidatus from the nearby palm trees into human dwellings may cause increasingly frequent outbreaks of oral Chagas disease.

House-level risk factors for Triatoma dimidiata infestation in Colombia

In Colombia, the main vectors of Trypanosoma cruzi, the causative agent of Chagas disease, are Rhodnius prolixus and Triatoma dimidiata. T. dimidiata is present in the east region of Colombia as domestic, peridomestic, and sylvatic populations, resulting in difficulties for its control. A cost-effective way to prioritize houses for treatment is to stratify houses based on risk factors. In this study, risk factors were evaluated for potential associations with domicile infestation of T. dimidiata. There was an increased likelihood of domestic infestation associated with the presence of mixed roofs (odds ratio [OR] = 36.14, 95% confidence interval [95% CI] = 12.21-106.97), cats (OR = 3.94, 95% CI = 1.36-11.38), rock piles (OR = 5.28, 95% CI = 1.64-16.98), and bushes with height above 10 m (OR = 11.21, 95% CI = 2.08-60.45). These factors could be used to target surveillance and control of T. dimidiata to houses with an increased risk of being infested.

Trypanosoma cruzi transmission in a Colombian Caribbean region suggests that secondary vectors play an important epidemiological role

Background

Colombia, as part of The Andean Countries Initiative has given priority to triatomine control programs to eliminate primary (domiciliated) vector species such as Rhodnius prolixus and Triatoma dimidiata. However, recent events of Trypanosoma cruzi transmission in localities where R. prolixus and T. dimidiata are not present suggest that other species are involved in the T. cruzi transmission cycle.

Methods

We studied T. cruzi transmission on Margarita Island, located on the Magdalena River in the Colombian Caribbean region, where a high number of non-domiciliated triatomines infected with T. cruzi inside human dwellings have been observed. A cross-sectional survey including serological studies in humans and parasitological and molecular methods in vectors and reservoirs was conducted. We investigated risk factors for human infection and house infestation, and evaluated the association between abundance of wild triatomines in palm trees (Attalea butyracea) across municipalities, seasons and anthropogenic land use.

Results

The T. cruzi seroprevalence rate in humans was 1.7% (13/743) and autochthonous active T. cruzi transmission was detected. The infection risk was associated with the capture of triatomines in human dwellings. Five wild mammal species were infected with T. cruzi, where Didelphis marsupialis was the main reservoir host with an 86.3% (19/22) infection rate. TcIb was the only genotype present among vectors. Triatomine abundance was significantly higher in Ecosystem 2, as well as in the dry season. Despite the absence of triatomine domiciliation in this area, T. cruzi active transmission was registered with a human seroprevalence rate similar to that reported in areas with domesticated R. prolixus.

Conclusions

This study illustrates the importance of secondary and household invading triatomines in Chagas disease epidemiology in the Caribbean lowlands of Colombia.

Trypanocidal drugs for chronic asymptomatic Trypanosoma cruzi infection

BACKGROUND

Prevention of chronic chagasic cardiomyopathy (CCC) by treating infected populations with trypanocidal therapy (TT) remains a challenge. Despite a renewed enthusiasm for TT, uncertainty regarding its efficacy, concerns about its safety and limited availability remain barriers for a wider use of conventional drugs. We have updated a previous version of this review.

OBJECTIVES

To systematically search, appraise, identify and extract data from eligible studies comparing the outcome of cohorts of seropositive individuals to Trypanosoma cruzi exposed to TT versus placebo or no treatment.

SEARCH METHODS

We sought eligible studies in electronic databases (Cochrane Central Register of Controlled Trials (CENTRAL), Issue 1, 2014); MEDLINE (Ovid, 1946 to January week 5 2014); EMBASE (Ovid, 1980 to 2014 week 6) and LILACS (up to 6 May 2010)) by combining terms related with the disease and the treatment. The search also included a Google search, handsearch for references in review or selected articles, and search of expert files. We applied no language restrictions.

SELECTION CRITERIA

Review authors screened the retrieved references for eligibility (those dealing with human participants treated with TT) and then assessed the pre-selected studies in full for inclusion. We included randomised controlled trials (RCTs) and observational studies that provided data on either mortality or clinical progression of CCC after at least four years of follow-up.

DATA COLLECTION AND ANALYSIS

Teams of two review authors independently carried out the study selection, data extraction and risk of bias assessment, with a referee resolving disagreement within the pairs. Data collection included study design, characteristics of the population and interventions or exposures and outcome measures. We defined categories of outcome data as parasite-related (positive serology, xenodiagnosis or polymerase chain reaction (PCR) after TT) and participant-related (including efficacy outcomes such as progression towards CCC, all-cause mortality and side effects of TT). We reported pooled outcome data as Mantel-Haenszel odds ratios (OR) or standardised mean differences (SMD) along with 95% confidence intervals (CI), using a random-effects model. I(2) statistics provided an estimate of heterogeneity across studies. We conducted an exploratory meta-regression analysis of the relationship between positive-serology and progression of CCC or mortality.

MAIN RESULTS

We included 13 studies involving 4229 participants (six RCTs, n = 1096, five RCTs of intermediate risk of bias, one RCT of high risk of bias; four non-randomised experiments, n = 1639 and three observational studies, n = 1494). Ten studies tested nitroderivative drugs nifurtimox or benznidazole (three exposed participants to allopurinol, one to itraconazole). Five studies were conducted in Brazil, five in Argentina, one in Bolivia, one in Chile and one in Venezuela.TT was associated with substantial, but heterogeneous reductions on parasite-related outcomes such as positive serology (9 studies, OR 0.21, 95% CI 0.10 to 0.44, I(2) = 76%), positive PCR (2 studies, OR 0.50, 95% CI 0.27 to 0.92, I(2) = 0%), positive xenodiagnosis after treatment (6 studies, OR 0.35, 95% CI 0.14 to 0.86, I(2) = 79%), or reduction on antibody titres (3 studies, SMD -0.56, 95% CI -0.89 to -0.23, I(2) = 28%). Efficacy data on patient-related outcomes was largely from non-RCTs. TT with nitroderivatives was associated with potentially important, but imprecise and inconsistent reductions in progression of CCC (4 studies, 106 events, OR 0.74, 95% CI 0.32 to 1.73, I(2) = 66%) and mortality after TT (6 studies, 99 events, OR 0.55, 95% CI 0.26 to 1.14, I(2) = 48%). The overall median incidence of any severe side effects among 1475 individuals from five studies exposed to TT was 2.7%, and the overall discontinuation of this two-month therapy in RCTs (5 studies, 134 events) was 20.5% (versus 4.3% among controls) and 10.4% in other five studies (125 events).

AUTHORS' CONCLUSIONS

Despite the evidence that TT reduced parasite-related outcomes, the low quality and inconsistency of the data for patient-important outcomes must be treated with caution. More geographically diverse RCTs testing newer forms of TT are warranted in order to 1. estimate efficacy more precisely, 2. explore factors potentially responsible for the heterogeneity of results and 3. increase knowledge on the efficacy/tolerance balance of conventional TT.

Using the basic reproduction number to assess the effects of climate change in the risk of Chagas disease transmission in Colombia

The dynamics of vector-borne diseases has often been linked to climate change. However the commonly complex dynamics of vector-borne diseases make it very difficult to predict risk based on vector or host distributions. The basic reproduction number (R0) integrates all factors that determine whether a pathogen can establish or not. To obtain R0 for complex vector-borne diseases one can use the next-generation matrix (NGM) approach. We used the NGM to compute R0 for Chagas disease in Colombia incorporating the effect of temperature in some of the transmission routes of Trypanosoma cruzi. We used R0 to generate a risk map of present conditions and a forecast risk map at 20 years from now based on mean annual temperature (data obtained from Worldclim). In addition we used the model to compute elasticity and sensitivity indexes on all model parameters and routes of transmission. We present this work as an approach to indicate which transmission pathways are more critical for disease transmission but acknowledge the fact that results and projections strongly depend on better knowledge of entomological parameters and transmission routes. We concluded that the highest contribution to R0 comes from transmission of the parasites from humans to vectors, which is a surprising result. In addition,parameters related to contacts between human and vectors and the efficiency of parasite transmission between them also show a prominent effect on R0.

Prevalence of Trypanosoma cruzi infection among people aged 15 to 89 years inhabiting the Department of Casanare (Colombia)

The purpose of this study was to calculate the seroprevalence of Trypanosoma cruzi infection in a sample of inhabitants from a region considered to be at high risk of natural transmission of Chagas disease in Colombia. A cross-sectional study was conducted in subjects from 5 municipalities, recruited in urban and rural locations, distributed by gender according to the demographic information available. Socio-demographic information, history of potential exposure to insect vectors, blood donating, as well as symptoms suggesting cardiac disease were collected using a questionnaire. After giving written informed consent, blood specimens were obtained from 486 people to determine the serologic evidence of past exposure to T. cruzi. Infection was diagnosed when two different tests (ELISA and IHA) were positive. The seroprevalence of antibodies against T. cruzi was 16.91% considering an estimated population of 44,355 aged between 15 and 89 years (95%IC: 13.72 to 20.01). The factors significantly associated with the infection were: 1- Housing materials like vegetable material, adobe or unfinished brick walls; 2- The fact of having previous tests for Chagas disease (regardless of the result). Of note, the mean ages among infected and not infected participants were significantly different (49.19 vs. 41.66, p≤0.0001). Among the studied municipalities, the one with the highest frequency of T. cruzi infection was Nunchia, with 31.15% of the surveyed subjects. Therefore it may be concluded that T. cruzi infection is highly prevalent in the north region of Casanare, in Colombia.

Chagas disease is caused by the chronic infection with the parasite Trypanosoma cruzi and is transmitted to human beings by bloodsucking insects of the Triatoma family. This condition is endemic in Central and South America, and is acquiring relevance in the rest of the world since it can also be transmitted by transfusions or organ transplantation from asymptomatic, infected donors. Detecting infected persons is one of the most important points in public health, mostly because it allows the identification of infected individuals at earlier stages of the disease, where adequate medical surveillance will permit secondary prevention measures to be given to these patients and thus avoidance of disease complications such as cardiac arrhythmia and heart failure. In this study we describe the prevalence of infection in a region of Colombia that was previously considered at risk for the infection because of the presence of infected insect vectors living in housings.

Understanding the role of dogs (Canis lupus familiaris) in the transmission dynamics of Trypanosoma cruzi genotypes in Colombia

The dog (Canis lupus familiaris) is the most important domestic reservoir of Chagas disease, a zoonosis that affects more than 10 million people in Latin America. Trypanosoma cruzi, the etiologic agent of the disease, displays remarkable genetic variability, as indicated by its six genotypes (TcI-TcVI). A pilot study was conducted to establish the prevalence of T. cruzi among the canine population by analyzing 80 dogs. We report the identification of the TcI, TcII, TcIV and TcVI genotypes as single infections. TcI/TcII and TcI/TcIV presented as mixed infections and included the presence of Trypanosoma angel. The implications of this distribution are herein discussed. Based on the molecular epidemiology findings, this study suggests a plausible role for canine synanthropism in the transmission of T. cruzi.

A field trial of alternative targeted screening strategies for Chagas disease in Arequipa, Peru

BACKGROUND

Chagas disease is endemic in the rural areas of southern Peru and a growing urban problem in the regional capital of Arequipa, population ∼860,000. It is unclear how to implement cost-effective screening programs across a large urban and periurban environment.

METHODS

We compared four alternative screening strategies in 18 periurban communities, testing individuals in houses with 1) infected vectors; 2) high vector densities; 3) low vector densities; and 4) no vectors. Vector data were obtained from routine Ministry of Health insecticide application campaigns. We performed ring case detection (radius of 15 m) around seropositive individuals, and collected data on costs of implementation for each strategy.

RESULTS

Infection was detected in 21 of 923 (2.28%) participants. Cases had lived more time on average in rural places than non-cases (7.20 years versus 3.31 years, respectively). Significant risk factors on univariate logistic regression for infection were age (OR 1.02; p = 0.041), time lived in a rural location (OR 1.04; p = 0.022), and time lived in an infested area (OR 1.04; p = 0.008). No multivariate model with these variables fit the data better than a simple model including only the time lived in an area with triatomine bugs. There was no significant difference in prevalence across the screening strategies; however a self-assessment of disease risk may have biased participation, inflating prevalence among residents of houses where no infestation was detected. Testing houses with infected-vectors was least expensive. Ring case detection yielded four secondary cases in only one community, possibly due to vector-borne transmission in this community, apparently absent in the others.

CONCLUSIONS

Targeted screening for urban Chagas disease is promising in areas with ongoing vector-borne transmission; however, these pockets of epidemic transmission remain difficult to detect a priori. The flexibility to adapt to the epidemiology that emerges during screening is key to an efficient case detection intervention. In heterogeneous urban environments, self-assessments of risk and simple residence history questionnaires may be useful to identify those at highest risk for Chagas disease to guide diagnostic efforts.

The role of parasite persistence in pathogenesis of Chagas heart disease

Chagas disease (CD) is caused by the infection with the protozoan haemoflagellate Trypanosoma cruzi. This disease is still a great menace to public health, and is largely neglected as it affects mostly the poorest populations of Latin America. Nonetheless, there are neither effective diagnostic markers nor therapeutic options to accurately detect and efficiently cure this chronic infection. In spite of the great advances in the knowledge of the biology of natural transmission, as well as the immunobiology of the host-parasite interaction, the understanding of the pathogenesis of CD remains largely elusive. In the recent decades, a controversy in the research community has developed about the relevance of parasite persistence or autoimmune phenomena in the development of chronic cardiac pathology. One of the most notable aspects of chronic CD is the progressive deterioration of cardiac function, derived mostly from structural derangement, as a consequence of the intense inflammatory process. Here we review the evidence supporting the multifactorial nature of Chagas heart disease comprising pathogen persistence and altered host immunoregulatory mechanisms.

Haplotype identification within Trypanosoma cruzi I in Colombian isolates from several reservoirs, vectors and humans

Genetic variability in the Trypanosoma cruzi I group has recently been revealed in Colombian isolates from humans, reservoirs and vectors. Genomic rearrangements and the polymorphic regions in taxonomic markers, such as the miniexon gene, have led to the development of molecular tools to identify phylogenetic haplotypes in T. cruzi isolates. From genetic polymorphisms found in T. cruzi I isolates, they have been classified into four haplotypes according to their epidemiologic transmission cycles. Haplotype Ia is associated with domestic isolates, from Rhodnius prolixus; haplotype Ib, with the domestic and peridomestic cycle, mainly associated with Triatoma dimidiata; haplotype Ic is a poorly characterized group, which has been associated with the peridomestic cycle; and haplotype Id has been related to the sylvatic cycle. In order to demonstrate that the circulating T. cruzi I isolates in Colombia can be classified in the four proposed haplotypes, specific primers were designed on polymorphic regions of the miniexon gene's intergenic sequences. This set of primers allowed the molecular characterization of 33 Colombian isolates, classifying them into three of the four proposed haplotypes (Ia, Ib and Id). Results obtained from maximum parsimony and maximum-likelihood-based phylogenetic analyses correlated with the molecular classification of the isolates and their transmission cycles. This study brings insights into the Chagas disease epidemiology and the parasite's transmission dynamics.

A panel of ten microsatellite loci for the Chagas disease vector Rhodnius prolixus (Hemiptera: Reduviidae)

Rhodnius prolixus is the main vector of Chagas disease in Venezuela, where it is found colonising rural housing consisting of unplastered adobe walls with palm and/or metal roofs. Vector control failure in Venezuela may be due to the invasion of houses by silvatic populations of R. prolixus found in palms. As part of a study to determine if domestic and silvatic populations of R. prolixus are isolated, thus clarifying the role of silvatic populations in maintaining house infestations, we constructed three partial genomic microsatellite libraries. A panel of ten dinucleotide polymorphic microsatellite markers was selected for genotyping. Allele numbers per locus ranged from three to twelve, with observed and expected heterozygosity ranging from 0.26 to 0.55 and 0.32 to 0.66. The microsatellite markers presented here will contribute to the control of Chagas disease in Venezuela and Colombia through the provision of population information that may allow the design of improved control strategies.

Molecular genetics reveal that silvatic Rhodnius prolixus do colonise rural houses

BACKGROUND

Rhodnius prolixus is the main vector of Chagas disease in Venezuela. Here, domestic infestations of poor quality rural housing have persisted despite four decades of vector control. This is in contrast to the Southern Cone region of South America, where the main vector, Triatoma infestans, has been eliminated over large areas. The repeated colonisation of houses by silvatic populations of R. prolixus potentially explains the control difficulties. However, controversy surrounds the existence of silvatic R. prolixus: it has been suggested that all silvatic populations are in fact Rhodnius robustus, a related species of minor epidemiological importance. Here we investigate, by direct sequencing (mtcytb, D2) and by microsatellite analysis, 1) the identity of silvatic Rhodnius and 2) whether silvatic populations of Rhodnius are isolated from domestic populations.

METHODS AND FINDINGS

Direct sequencing confirmed the presence of R. prolixus in palms and that silvatic bugs can colonise houses, with house and palm specimens sharing seven cytb haplotypes. Additionally, mitochondrial introgression was detected between R. robustus and R. prolixus, indicating a previous hybridisation event. The use of ten polymorphic microsatellite loci revealed a lack of genetic structure between silvatic and domestic ecotopes (non-significant F(ST) values), which is indicative of unrestricted gene flow.

CONCLUSIONS

Our analyses demonstrate that silvatic R. prolixus presents an unquestionable threat to the control of Chagas disease in Venezuela. The design of improved control strategies is essential for successful long term control and could include modified spraying and surveillance practices, together with housing improvements.

Modelling geographic variation in the cost-effectiveness of control policies for infectious vector diseases: the example of Chagas disease

Few cost-effectiveness analysis (CEA) models have accounted for geographic variation in input parameters. This paper describes a deterministic discrete-time multi-state model to estimate the cost-effectiveness of vector control policies for Chagas disease, where implementation varies according to village characteristics. The model outputs include the total number of new infections, disability adjusted life years (DALYs) incurred, costs of associated healthcare, and total costs of the Ministry of Health's control policy for house surveillance and spraying. Incremental net benefits were estimated to determine Colombian villages in which it is cost-effective to implement the control policy. The robustness of these conclusions was evaluated by deterministic sensitivity analyses. The model should help provide a decision-support system to compare control policies and to allocate resources geographically.

Chagas disease in Andean countries

The Andean Countries' Initiative (ACI) for controlling Chagas disease was officially created in 1997 within the framework of the Hipolito Unanue Agreement (UNANUE) between the Ministries of Health of Colombia, Ecuador, Peru, and Venezuela. Its objective was to interrupt transmission via vector and transfusion in the region, taking into account that there are 12.5 million people at risk in the four Andean countries forming the initiative in the area and around 3 million people are infected by Trypanosoma cruzi. The progress of control activities for the vector species present in the Andean sub-region, for different reasons, has been slow and control interventions have still not been installed in all geographical areas occupied by the target species. This has been partly due to lack of knowledge about these vector populations' biological characteristics, and consequent uncertainty about which are the appropriate control measures and strategies to be implemented in the region. The main vector species present important similarities in Venezuela and Colombia and in Ecuador and Northern Peru and they can be approached in a similar way throughout the whole regions, basing approaches on and adapting them to the current strategies being developed in Venezuela during the 1960s which have been progressively adopted in the Southern Cone and Central-American region. Additional measures are needed for keeping endemic areas free from Rhodnius prolixus silvatic populations, widely spread in the Orinoco region in Colombia and Venezuela. Regarding aetiological treatment, it is worth mentioning that (with the exception of Colombia) none of the other countries forming the ACI have registered medicaments available for treating infected young people. There are no suitable follow-up programmes in the sub-region or for treating cases of congenital Chagas disease. An integral and integrated programme encompassing all the aspects including transmission by transfusion which seems to have achieved extremely encouraging results in all countries, are urgently needed.

Neglected diseases, civil conflicts, and the right to health

Neglected diseases remain one of the largest causes of disease and mortality. In addition to the difficulties in provision of appropriate drugs for specific diseases, many other factors contribute to the prevalence of such diseases and the difficulties in reducing their burden. We address the role that poor governance and politically motivated oppression have on the epidemiology of neglected diseases. We give case examples including filariasis in eastern Burma and vector-borne diseases (Chagas' disease, leishmaniasis, and yellow fever) in Colombia, we show the links between systematic human rights violations and the effects of infectious disease on health. We also discuss the role of researchers in advocating for and researching within oppressed populations.

House-level risk factors for triatomine infestation in Colombia

BACKGROUND

Chagas disease, transmitted domestically by triatomine bugs, is the most important vector-borne disease in Latin America. The association between triatomine infestation and housing characteristics was investigated based on a standardized survey in 41 971 houses in 15 Departments in Colombia.

METHODS

Multivariate logistic regression was used to test for associations of two highly correlated infestation measures of infestation (householders reporting having seen triatomines inside the house, and sending triatomines to the survey team), with 15 household-level risk factors. Risks were measured relative to a reference category of houses with up to three inhabitants, area up to 50 m(2), unplastered adobe walls, thatch roof and no outbuildings or domestic animals.

RESULTS

The probability of seeing triatomines was highest for households with over seven inhabitants (OR = 1.24, 95% CI 1.11-1.39), overhead storage space (OR = 1.16, 95% CI 1.03-1.32), grain shed (OR = 1.25, 95% CI 1.02-1.52), cats (OR = 1.27, 95% CI 1.14-1.42) and pigs (OR = 1.16, 95% CI 1.03-1.30). Lowest risks were in houses with wooden walls (OR = 0.46, 95% CI 0.34-0.61), fully plastered walls (OR = 0.78, 95% CI 0.68-0.88), roofs made of tiles (OR = 0.51, 95% CI 0.33-0.78) and flagstone floors (OR = 0.57, 95% CI 0.42-0.76). Results for householders returning triatomines support this set of risk factors, but with wider confidence intervals.

CONCLUSIONS

Surveillance of a few easily assessed household characteristics provides an accurate, rapid assessment of house-level variation in risk. Measured effect sizes for specific structural characteristics could be used to maximize the cost-effectiveness of programmes to reduce vector infestation and interrupt Chagas disease transmission by improving house quality.

Morphometric evidence for a possible role of Rhodnius prolixus from palm trees in house re-infestation in the State of Barinas (Venezuela)

The main vector of Chagas disease in Venezuela is Rhodnius prolixus. Specimens of Rhodnius sp., identified elsewhere as R. prolixus by molecular tools, were collected in Barinas State (Venezuela) before insecticide application, and compared by morphometric techniques with post-spraying, re-infesting insects after control. Geometric morphometry was applied, allowing separate analyses of shape and size. The idea of a single species sharing silvatic and domestic/peri-domestic ecotopes was supported, suggesting new evolutionary scenarios for the controversial R. prolixus origins. The same data allowed to understand the possible mechanisms of villages re-infestation after a control campaign, either recolonization by local recovery of survivors or re-infestation by external migrants. Both mechanisms were apparent. Although shape properties could distinguish very close subpopulations such as insects from houses and insects from peri-domestic shelters, they were unable to identify the insects from palm trees as a distinct subpopulation. This strongly suggested that human environment could receive immigrants from palm trees. The pattern of size variation supported the hypothesis of a one-way exchange from silvatic to human environments, but did not support the reverse movement. Thus, morphometric data indicated that a silvatic population of the local vector is probably responsible for re-infesting villages after insecticide application, and they also pointed to the existence of re-infestation by local recovery of survivors. According to this interpretation, new epidemiological scenarios must be considered to improve Chagas disease control in Venezuela.

Characterization of ecto-phosphatase activities of Trypanosoma cruzi: a comparative study between Colombiana and Y strains

The etiological agent of Chagas disease, Trypanosoma cruzi, is consisted of two phylogenetic lineages. Using live epimastigotes, in this study we have characterized ecto-phosphatase activities of two strains of T. cruzi, one (Y strain) is a member of group T. cruzi I and the other (Colombiana) is a member of group T. cruzi II. About one-third of the total ecto-phosphatase activity from the Y strain was Mg(2+)-dependent, but no such activity was observed with Colombiana. The level of Mg(2+)-independent activity was dramatically different in the two strains, with Colombiana showing more than 15-fold higher activity. Experiments using classical inhibitors of acid phosphatases, as well as inhibitors of phosphotyrosine phosphatase, showed a decrease in these phosphatase activities, with different patterns of inhibition. The Mg(2+)-independent activities of the Colombiana and Y strains decreased inversely with pH, varying from 6.5 to 8.0. On the other hand, the Mg(2+)-dependent activity of the Y strain increased concomitantly with the increase in pH in the same range.