[1] Nihon Univ, Sch Med, Dept Pathol & Microbiol, Div Microbiol, Tokyo, Japan
[2] Univ Tokyo, Sch Int Hlth, Grad Sch Med, Dept Dev Med Sci, Tokyo, Japan
[3] Chiang Mai Univ, Fac Med, Dept Microbiol, Chiang Mai, Thailand
[4] Natl Inst Infect Dis, Dept Virol 2, Tokyo, Japan