Geographic shifts in Aedes aegypti habitat suitability in Ecuador using larval surveillance data and ecological niche modeling: Implications of climate change for public health vector control

Abstract

Arboviral disease transmission by Aedes mosquitoes poses a major challenge to public health systems in Ecuador, where constraints on health services and resource allocation call for spatially informed management decisions. Employing a unique dataset of larval occurrence records provided by the Ecuadorian Ministry of Health, we used ecological niche models (ENMs) to estimate the current geographic distribution of Aedes aegypti in Ecuador, using mosquito presence as a proxy for risk of disease transmission. ENMs built with the Genetic Algorithm for Rule-Set Production (GARP) algorithm and a suite of environmental variables were assessed for agreement and accuracy. The top model of larval mosquito presence was projected to the year 2050 under various combinations of greenhouse gas emissions scenarios and models of climate change. Under current climatic conditions, larval mosquitoes were not predicted in areas of high elevation in Ecuador, such as the Andes mountain range, as well as the eastern portion of the Amazon basin. However, all models projected to scenarios of future climate change demonstrated potential shifts in mosquito distribution, wherein range contractions were seen throughout most of eastern Ecuador, and areas of transitional elevation became suitable for mosquito presence. Encroachment of Ae. aegypti into mountainous terrain was estimated to affect up to 4,215 km2 under the most extreme scenario of climate change, an area which would put over 12,000 people currently living in transitional areas at risk. This distributional shift into communities at higher elevations indicates an area of concern for public health agencies, as targeted interventions may be needed to protect vulnerable populations with limited prior exposure to mosquito-borne diseases. Ultimately, the results of this study serve as a tool for informing public health policy and mosquito abatement strategies in Ecuador.

Fig 1. Ecuador, situated on the northwestern coast of South America (inset), has historically high prevalence of mosquito-borne diseases.

The Ecuadorian Ministerio de Salud Pública (MSP) conducted household entomological surveys of Aedes aegypti throughout the country from 2000–2012. Spatially unique larval index (LI) occurrence records (n = 478) collected in the survey were aggregated to cities and towns and used to model the ecological distribution of Ae. aegypti in Ecuador. This figure was produced in ArcMap 10.4 (ESRI, Redlands, CA) using shapefiles from the GADM database of Global Administrative Areas, ver. 2.8 (gadm.org), elevation data freely available from NASA’s Shuttle Radar Topography Mission (jpl.nasa.gov/srtm), and georeferenced mosquito surveillance data provided by the MSP and edited by CAL.

Fig 2. Agreement of best model subsets built with best-ranked suite of environmental variables for larval Aedes aegypti presence in Ecuador under current climate conditions.

Models had high levels of agreement in the western coastal lowlands, and lower levels of agreement in the eastern Amazon basin. This figure was produced in ArcMap 10.4 (ESRI, Redlands, CA) using rasters of model output produced with DesktopGARP (ver. 1.1.3), and elevation data freely available from NASA’s Shuttle Radar Topography Mission (jpl.nasa.gov/srtm).

Fig 3

Agreement of best model subsets built with best ranked suite of environmental variables for larval Aedes aegypti presence in Ecuador under A) current climate conditions and future climate conditions projected to the year 2050 under Representative Concentration Pathway (RCP) 2.6 (B1,C1,D1) and 8.5 (B2,C2,D2) for the B) BCC-CSM-1, C) CCSM4, and D) HADGEM2-ES General Circulation Models (GCM) climate models. This figure was produced in ArcMap 10.4 (ESRI, Redlands, CA) using rasters of model output produced with DesktopGARP (ver. 1.1.3), and elevation data freely available from NASA’s Shuttle Radar Topography Mission (jpl.nasa.gov/srtm).

Fig 4. Best model subsets for current and future climate (GCMs projected to the year 2050) were combined by RCP emissions scenarios to illustrate the estimated contraction and expansion of larval Aedes aegypti geographic range in Ecuador.

This figure was produced in ArcMap 10.4 (ESRI, Redlands, CA) using rasters of model output produced with DesktopGARP (ver. 1.1.3), and elevation data freely available from NASA’s Shuttle Radar Topography Mission (jpl.nasa.gov/srtm).