1. Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
2. Woodrow Wilson School, Princeton University, Princeton, NJ 08544, USA.
3. Centre for Infectious Disease Dynamics, Pennsylvania State University, State College, PA 16801, USA.
4. Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA.
5. Department of Geography and Environment, University of Southampton, Southampton SO17 1BJ, UK.
6. Fogarty International Center, National Institutes of Health, Bethesda, MD 20892, USA.
7. Flowminder Foundation, 17177 Stockholm, Sweden.