This project will explore the ecology of Aedes (Ae.) aegypti, the mosquito that transmits dengue, yellow fever and chikungunya. We hypothesize that the combined effects of climate variability and changes made by humans to their local environment can influence key aspects of both mosquito ecology and human behavior. Studying this system as a whole will improve our ability to predict risks of mosquito vector and dengue virus exposure and the possible impacts of future climate change.
Dengue viruses circulate between mosquitoes and humans, causing an estimated 100 million human dengue infections annually. In the last decade, the Americas have experienced a dramatic increase in severe cases (dengue hemorrhagic fever), with devastating public health consequences. As neither vaccines nor therapeutics are yet available, mosquito control is the main option for preventing and controlling dengue outbreaks. Efforts in this area have been hindered by a poor understanding of the dengue virus transmission system at the interface between its natural and human components. Of particular concern is the potential for dengue fever to expand into areas that are presently outside transmission zones but may become vulnerable under scenarios of future climate change. For example, this potential expansion poses a risk to the ~19 million people in and near Mexico City, a high altitude "island" currently free of dengue but surrounded by dengue virus transmission at lower altitudes.
Specific aims of the project are to: (1) determine how weather/climate factors are related to the presence and abundance of disease-carrying mosquitoes, especially by serving as barriers to mosquitoes becoming established in an area; (2) use these results in high-resolution atmospheric models to develop a predictive model for future mosquito range expansion; (3) determine which aspects of human behavior and attributes of man-made environments are most closely related to Ae. aegypti presence and abundance; (4) employ state-of-the-science data assimilation procedures to validate, refine, and define uncertainty in this modeling framework. Key aspects of this coupled natural and human system will be studied along an altitudinal transect in Mexico, ranging from coastal, low-elevation environments with well established vector mosquito populations and intense dengue virus transmission to high-elevation, mountainous areas which currently are free of the mosquito vector and local virus transmission. The team of experts from Mexico and the United States includes climatologists, vector ecologists, modelers and medical anthropologists.
The project will contribute essential insights into the ongoing debate about climate change and infectious disease relationships, extending beyond the explicit vector ecology and geographic boundaries of this study. The work will provide quantitative knowledge that can be used to develop novel strategies to control Ae. aegypti in the face of future threats to system resilience. Further, it will provide training for a postdoctoral fellow in climate modeling and spatial risk modeling at both Colorado State University and the National Center for Atmospheric Research and involvement and in situ training of university and secondary school students in data collection. Through "participatory epidemiology", local community members will learn how to use environmental observation and data collection as a means of community empowerment.
Intellectual Merit: We worked for several years along an elevation/climatic transect in 12 communities in eastern Mexico extending from Veracruz City at sea level to Puebla City at about 2,100 m above sea level (ASL), in order to characterize the coupled natural-human system for dengue virus vector mosquito Aedes aegypti throughout its entire climatic range. Aedes aegypti presence was strongly correlated with temperature; the discovery of Aedes aegypti on repeated occasions at 2,100 m ASL – about 300 m higher than it has ever been found in Mexico – suggests observed warming of about 1oC during the past 50 years may be contributing to the movement of Aedes aegypti toward cooler, higher elevations. The Water Height And Temperature in Container Habitats Energy Model (WHATCH’EM), which simulates conditions in containers that Aedes aegypti uses for its early life stages, was developed and field-validated under this project (Figure 1). The model is open source and freely available to anyone. WHATCH’EM is now being leveraged for use in several other projects, including serving as a key component in a recently developed prototype dengue surveillance system. Broader Impacts: The team developed a "participatory epidemiology" approach to engage high school and university students in the use of environmental observation and data collection as a means of community empowerment. For the high school students, the approach involved the installation of mini weather stations at several schools and training students to collect Aedes aegypti eggs via ovitraps. Students then compared egg counts to the weather data to assess correlations between egg presence/abundance and meteorological conditions. For the university students it involved participating directly in multidisciplinary field collections. In May 2013, a wrap-up workshop was held in Xalapa, Veracruz, Mexico and students presented their work and discussed challenges and potential local solutions associated with data collection, and future research directions (Figure 2). A workshop that provided background training in numerical weather modeling was also held in Xalapa, Veracruz, Mexico in May 2013. Three postdoctoral researchers received interdisciplinary training on the project.
