[1] Univ Liverpool, Dept Neurol Sci, Walton Ctr Neurol & Neurosurg, Liverpool L9 7LJ, Merseyside, England
[2] Univ Liverpool, Liverpool Sch Trop Med, Liverpool L3 5QA, Merseyside, England
[3] Cho Quan Hosp, Ctr Trop Dis, Ho Chi Minh City, Vietnam
[4] Royal Liverpool Childrens NHS Trust, Liverpool L12 2AP, Merseyside, England
[5] John Radcliffe Hosp, Ctr Trop Med & Infect Dis, Nuffield Dept Clin Med, Oxford OX3 9DU, England
[6] Walter Reed Army Med Ctr, Walter Reed Army Inst Res, Dept Virus Dis, Washington, DC 20307 USA