[1] George Washington Univ, Dept Microbiol & Trop Med, Washington, DC 20037 USA
[2] London Sch Hyg & Trop Med, Dept Infect & Trop Dis, London WC1, England
[3] Queensland Inst Med Res, Div Infect Dis & Immunol, Brisbane, Qld 4006, Australia
[4] Chinese Ctr Dis Control & Prevent, Inst Parasit Dis, Shanghai, Peoples R China