[1] Univ Oxford, Nuffield Dept Clin Med, Ctr Trop Med, Oxford, England
[2] Univ London Imperial Coll Sci Technol & Med, Dept Biol Sci, Ctr Mol Microbiol & Infect, London SW7 2AZ, England
[3] Mahidol Univ, Fac Trop Med, Oxfrod Trop Med Res Programme, Wellcome Trust Mahidol Univ, Bangkok, Thailand