[1] NIH, Fogarty Int Ctr, Bethesda, MD 20892 USA
[2] Univ Cambridge, Dept Appl Math & Theoret Phys, Ctr Math Sci, Cambridge CB3 OWA, England
[3] Univ Warwick, Warwick Infect Dis Epidemiol Res Ctr WIDER, Coventry CV4 7AL, W Midlands, England
[4] Univ Warwick, Warwick Math Inst, Coventry CV4 7AL, W Midlands, England
[5] Univ Cambridge, Dept Vet Med, Dis Dynam Unit, Cambridge CB3 0ES, England
[6] Univ Oxford, Oxford Martin Sch, Dept Zool, Oxford OX1 3P5, England
[7] Univ London Imperial Coll Sci Technol & Med, Sch Publ Hlth, Dept Infect Dis Epidemiol, London SW7 2AZ, England
[8] Univ Calif Los Angeles, Dept Ecol & Evolutionary Biol, Los Angeles, CA 90095 USA