VARIANTS OF JAPANESE ENCEPHALITIS VIRUS CYTOPATHIC FOR L MOUSE FIBROBLASTS AND LASS HUMAN EPITHELIAL CELLS

Abstract

Serial passage of Japanese encephalitis (JE) virus, strain 281801 from heron blood, in L mouse fibroblastic cell cultures produces a variant virus with enhanced cytopathic effects (CPE) for L cells. Similarly serial passage of infected Lass human epithelial cells and virus in carrier cultures of strain M5/596 from mosquitoes yielded a variant virus with increased CPE for Lass, though not for HeLa human epithelial cells. Such results did not always occur however, because in another series of carrier cultures, Lass cells gained the upper hand and virus disapeared after 11 passages and 257 days. Although unadapted JE virus produced cytopathic effects in cultures of Lass cells, this CPE involved less than 10% of cells and was quickly repaired by migrating healthy cells even though it correlated with production of infectious virus into the cultural fluid. Titers of the L cell variant virus were higher in L cell cultures than in weanling mice inoculated intracranially, but were similar for the Lass cell variant in mice and in Lass cell cultures based on CPE or infectivity.