[1] Mahidol Univ, Fac Trop Med, Mahidol Oxford Trop Med Res Unit, Bangkok 10400, Thailand
[2] Ubon Ratchathani Hosp, Sappasithiprasong Hosp, Dept Med, Ubon Ratchathani 34000, Thailand
[3] Univ Oxford, Churchill Hosp, Nuffield Dept Clin Med, Ctr Clin Vaccinol & Trop Med, Oxford OX3 7LJ, England