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

Abstract

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