[1] Yamaguchi Univ, Sch Med, Dept Internal Med 1, Ube, Yamaguchi 7558505, Japan
[2] Yamaguchi Univ, Sch Med, Dept Pathol 2, Ube, Yamaguchi 7558505, Japan
[3] Yamaguchi Univ, Sch Med, Dept Microbiol, Ube, Yamaguchi 7558505, Japan
[4] Tokyo Med & Dent Univ, Med Res Inst, Dept Virol, Tokyo, Japan
[5] Hokkaido Univ, Sch Med, Inst Canc, Dept Virol, Sapporo, Hokkaido 060, Japan