1 Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, USA; Fogarty International Center, National Institute of Health, Bethesda, MD, USA. Electronic address: cmetcalf@princeton.edu.
2 Wellcome Trust, Gibbs Building, London, UK.
3 London School of Hygiene & Tropical Medicine, London, UK.
4 Fogarty International Center, National Institute of Health, Bethesda, MD, USA; Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, Minneapolis, MN, USA.
5 Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, USA; Fogarty International Center, National Institute of Health, Bethesda, MD, USA.
6 Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
7 Department of Medicine, School of Public Health, Imperial College London, London, UK.
8 Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA.