[1] Natl Inst Infect Dis, Dept Virol 1, Tokyo 2080011, Japan
[2] Natl Inst Infect Dis, Dept Bacteriol 2, Tokyo 2080011, Japan
[3] Natl Inst Infect Dis, Dept Virol 2, Tokyo 2080011, Japan
[4] Natl Inst Infect Dis, Div Expt Anim Res, Tokyo 2080011, Japan
[5] Rakuno Gakuen Univ, Sch Vet Med, Lab Vet Radiol, Ebetsu, Hokkaido 069, Japan