We cultured BHK-21, Vero and C6/36 Aedes albopictus cells as previously described 35 24, 36) . We also performed neutralization experiments with prototype strains of St. Louis (59268 (Parton)) and Japanese encephalitis (Nakayama) viruses 37 . For in vivo experiments, viruses were diluted and injected into mice as described 23 .