Research needs for Chagas disease prevention.

We present an overview of the two main strategies for the primary (vector control) and secondary (patient care) prevention of Chagas disease (CD). We identify major advances, knowledge gaps, and key research needs in both areas. Improved specific chemotherapy, including more practical formulations (e.g., paediatric) or combinations of existing drugs, and a better understanding of pathogenesis, including the relative weights of parasite and host genetic makeup, are clearly needed. Regarding CD vectors, we find that only about 10-20% of published papers on triatomines deal directly with disease control. We pinpoint the pitfalls of the current consensus on triatomine systematics, particularly within the Triatomini, and suggest how some straightforward sampling and analytical strategies would improve research on vector ecology, naturally leading to sounder control-surveillance schemes. We conclude that sustained research on CD prevention is still crucial. In the past, it provided not only the know-how, but also the critical mass of scientists needed to foster and consolidate CD prevention programmes; in the future, both patient care and long-term vector control would nonetheless benefit from more sharply focused, problem-oriented research

The ecology and genetics of Chagas disease vectors in Ecuador, with emphasis on Rhodnius ecuadoriensis (Hemiptera: Reduviidae: Triatominae)

An estimate >11 million people are infected by Trypanosoma cruzi in Latin America. Chagas disease control programmes have been successful in the Southern Cone countries, and similar initiatives are underway in the Andean countries. In Ecuador prevalence is estimated as ~ 130000 people, with 2.5-3.8 million at risk; annual associated costs may reach >20 million US dollars. We studied ecological, genetic, and evolutionary aspects of Rhodnius ecuadoriensis, an important disease vector in western Ecuador and northwestern Peru. Sylvatic and synanthropic populations are sympatric in central Ecuador; only domestic-peridomestic colonies occur in the temperate Andean valleys of southern Ecuador and northern Peru. Both morphological-chromatic features and ecological-behavioural preferences seem to define a cline [sylvatic-large (north) - synanthropic-small (south)]. The ecology of domestic and sylvatic populations was studied using logistic regression. Phytelephas aequatorialis palms are the primary natural ecotope of R ecuadoriensis; sylvatic bugs tend to favour male palms with large amounts of decomposing organic material and located in cropland/pasture fields. Poor households with mud walls, tiled roofs and large numbers of chickens were more likely to be infested. Isometry-free morphometric analysis consistently achieved >90% correct discrimination of sylvatic vs. synanthropic populations, supporting the use of metric variables in surveillance of reinfestations; size-free analyses revealed substantial divergence of Peruvian bugs from La Libertad. Mitochondrial DNA sequence polymorphisms (cytochrome b gene, 663 basepairs) were analysed; ~4% sequence divergence scored between Ecuadorian and Peruvian populations suggested they are independent phylogroups. Haplotype diversity and relationships indicate central coastal Ecuador as the centre of dispersal of this species, with isolated domestic populations in dry Andean valleys. The phylogeny of this species was explored using morphometric and molecular approaches. The monophyly of the `Pacific Rhodnius lineage' (pallescens, colombiensis and ecuadoriensis) was confirmed, with the parapatric pallescens and colombiensis being very closely related; R. pictipes is the closest relative to this lineage among Amazonian species, with the robustus group forming a distinct, major Glade. Control of R ecuadoriensis can contemplate local eradication in dry Andean valleys (southern Ecuador and northern Peru); special attention should be paid to peridomestic populations, including improvement of poultry management (burning-replacing nests every 15-30 days). Long-term interruption of disease transmission would benefit from educational interventions increasing awareness about Chagas disease and from housing improvements targeting mud walls and timber-and-tile roofs. In central-northern western Ecuador peridomestic palm trees may be the origin of reinfestations; environmental management (removing dead fronds and fibres from peridomestic palms), and continuous community- based surveillance are recommended. A comprehensive control programme over 15 years would probably result in interruption of disease transmission, and could bring savings of about 20 US$ per each dollar invested.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Community Participation in Chagas Disease Vector Surveillance: Systematic Review

Blood-sucking triatomine bugs are the vectors of Chagas disease, a potentially fatal illness that affects millions in Latin America. With no vaccines available, prevention heavily depends on controlling household-infesting triatomines. Insecticide-spraying campaigns have effectively reduced incidence, but persistent household reinfestation can result in disease re-emergence. What, then, is the best strategy to keep houses free of triatomines and thus interrupt disease transmission in the long run? We reviewed published evidence to (i) assess the effectiveness of insecticide-based vector control, gauging the importance of reinfestation; (ii) compare the efficacy of programme-based (with households periodically visited by trained staff) and community-based (with residents reporting suspect vectors found in their homes) surveillance strategies; and (iii) evaluate the performance of alternative vector-detection methods. The results confirm that insecticide-based vector control is highly effective, but also that persistent house reinfestation is a general trend across Latin America. Surveillance systems are significantly more effective when householders report suspect bugs than when programme staff search houses, either manually or using vector-detection devices. Our results clearly support the view that long-term vector surveillance will be necessary for sustained Chagas disease control – and that community participation can substantially contribute to this aim

Certifying the interruption of Chagas disease transmission by native vectors : cui bono?

Certifying the absence of Chagas disease transmission by native vectors lacks scientific grounds and weakens long-term control-surveillance systems to the detriment of people living under risk conditions. Instead, a regular "certification of good practice" (including vector control-surveillance, case detection/patient care and blood safety) could help achieve sustained disease control

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.Fil: Rojas de Arias, Antonieta. Centro para el Desarrollo de la Investigación Científica; ParaguayFil: Monroy, Carlota. Universidad de San Carlos de Guatemala (univ. de San C. de Guatemala);Fil: Guhl, Felipe. Universidad de los Andes; ColombiaFil: Sosa-Estani, Sergio Alejandro. Drugs For Neglected Diseases Initiative; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Epidemiología y Salud Pública. Instituto de Efectividad Clínica y Sanitaria. Centro de Investigaciones en Epidemiología y Salud Pública; ArgentinaFil: Santos, Walter Souza. Ministério da Saúde; BrasilFil: Abad Franch, Fernando. Universidade do Brasília; Brasi

Epidemiology of Chagas disease in Ecuador. A brief review

Chagas disease is a complex public health problem that has been underestimated in Ecuador. Here we review the relevant published information, and present unpublished and new data that help to understand the current Chagas disease epidemiological situation and its evolution in the country. Three main characteristics have been identified: (i) persistence of Trypanosoma cruzi transmission in already known foci; (ii) a marked endemicity in some urban areas of Guayaquil; and (iii) the transformation of new Amazon foci into truly endemic areas. The situation in other suspect areas remains uncertain. Five Triatominae species have been implicated in the transmission of T. cruzi to people in Ecuador (Triatoma dimidiata, Rhodnius ecuadoriensis, R. pictipes, R. robustus and Panstrongylus geniculatus), but some others may also play a role in some areas (P. rufotuberculatus, P. howardi, T. carrioni and P. chinai). Other Triatominae reported seem to have little or no epidemiological relevance (T. venosa, T. dispar, Eratyrus mucronatus, E. cuspidatus, P. lignarius and Cavernicola pilosa). High frequency of acute cases and severe chronic disease has been observed. Although cardiomyopathy is more frequent, serious digestive disease is also present. It is estimated that around 120,000-200,000 people may be infected. 2.2 to 3.8 million people are estimated to live under transmission risk conditions

Insights from quantitative and mathematical modelling on the proposed WHO 2030 goals for Chagas disease

article publié sur la plateforme Gates Open researchChagas disease (CD) persists as one of the neglected tropical diseases (NTDs) with a particularly large impact in the Americas. The World Health Organization (WHO) recently proposed goals for CD elimination as a public health problem to be reached by 2030 by means of achieving intradomiciliary transmission interruption (IDTI), blood transfusion and transplant transmission interruption, diagnostic and treatment scaling-up and prevention and control of congenital transmission. The NTD Modelling Consortium has developed mathematical models to study Trypanosoma transmission dynamics and the potential impact of control measures. cruzi Modelling insights have shown that IDTI is feasible in areas with sustained vector control programmes and no presence of native triatomine vector populations. However, IDTI in areas with native vectors it is not feasible in a sustainable manner. Combining vector control with trypanocidal treatment can reduce the timeframes necessary to reach operational thresholds for IDTI (<2% seroprevalence in children aged <5 years), but the most informative age groups for serological monitoring are yet to be identified. Measuring progress towards the 2030 goals will require availability of vector surveillance and seroprevalence data at a fine scale, and a more active surveillance system, as well as a better understanding of the risks of vector re-colonization and disease resurgence after vector control cessation. Also, achieving scaling-up in terms of access to treatment to the expected levels (75%) will require a substantial increase in screening asymptomatic populations, which is anticipated to become very costly as CD prevalence decreases. Further modelling work includes refining and extending mathematical models (including transmission dynamics and statistical frameworks) to predict transmission at a sub-national scale, and developing quantitative tools to inform IDTI certification, post-certification and re-certification protocols. Potential perverse incentives associated with operational thresholds are discussed. These modelling insights aim to inform discussions on the goals and treatment guidelines for CD

Modeling Disease Vector Occurrence when Detection Is Imperfect: Infestation of Amazonian Palm Trees by Triatomine Bugs at Three Spatial Scales

Blood-sucking bugs of the genus Rhodnius are major vectors of Chagas disease. Control and surveillance of Chagas disease transmission critically depend on ascertaining whether households and nearby ecotopes (such as palm trees) are infested by these vectors. However, no bug detection technique works perfectly. Because more sensitive methods are more costly, vector searches face a trade-off between technical prowess and sample size. We compromise by using relatively inexpensive sampling techniques that can be applied multiple times to a large number of palms. With these replicated results, we estimate the probability of failing to detect bugs in a palm that is actually infested. We incorporate this information into our analyses to derive an unbiased estimate of palm infestation, and find it to be about 50% – twice the observed proportion of infested palms. We are then able to model the effects of regional, landscape, and local environmental variables on palm infestation. Individual palm attributes contribute overwhelmingly more than landscape or regional covariates to explaining infestation, suggesting that palm tree management can help mitigate risk locally. Our results illustrate how explicitly accounting for vector, pathogen, or host detection failures can substantially improve epidemiological parameter estimation when perfect detection techniques are unavailable