Interspecies interactions of arboviruses. II. Participation of the genomes of two flaviviruses, West Nile and Japanese encephalitis, in formation of a virus clone with dual antigenic determinants.

A peculiar clone, 41/WN+JE+, possessing antigenic determinants of a flaviviruses, West Nile (WN) and Japanese encphalitis (JE), is described. The antigenic duality of this clone exceeded the cross reactions between WN and JE viruses; either antiserum neutralized 104--105 PFU/ml of the virus. The property of antigenic duality was inherited in over 340 virus generations and retained upon propagation in selective cell systems and after recloning. The progeny of infectious RNA consisted of 3 types of virus particle: antigenetically distinct WN and JE viruses and particles retaining dual antigenic determinants WN+JE+. The nature of clone 41/WN+JE+ (a stable heterozygote accompanied by phenotypic mixing) and its origin due to inadvertent contamination of attenuated WN virus with JE virus is discussed.