[1] Univ London London Sch Hyg & Trop Med, Dept Infect & Trop Dis, London WC1E 7HT, England
[2] Ctr Geog Med Res, Kenya Med Res Inst, Coast Wellcome Trust Collaborat Program, Kilifi, Kenya
[3] BPRC, Dept Parasitol, NL-2280 GH Rijswijk, Netherlands
[4] Walter Reed Army Inst Res, Dept Immunol, Silver Spring, MD 20910 USA
[5] Univ Oxford, John Radcliffe Hosp, Nuffield Dept Clin Med, Ctr Trop Med, Oxford OX3 9DY, England
[6] Swiss Trop Inst, Dept Epidemiol & Publ Hlth, CH-4003 Basel, Switzerland