Genetic differences of E gene of a Thai strain of Japanese encephalitis virus that determine small plaque size phenotype but not neurovirulence in suckling mice.

Two small plaque variants of Japanese encephalitis virus (JEV), S4P9 and S9P10, were recovered from the wild type of JEV strain KE-093 using plaque purification in combination with the temperature-shift induction technique. Growth patterns of the S4P9 and S9P10 in BHK-21 cells as well as neurovirulence in suckling mice were similar to that of KE-093. An amino acid substitution, lysine for glutamic acid, was present in envelope protein at residue E-83 in the small plaque variants. This study shows that small plaque phenotype is not always associated with attenuation in vivo.