MOLECULAR DIFFERENCES BETWEEN WILD-TYPE JAPANESE ENCEPHALITIS-VIRUS STRAINS OF HIGH AND LOW MOUSE NEUROINVASIVENESS

Japanese encephalitis (JE) virus strain P3 was highly neurovirulent an d neuroinvasive in weanling mice whereas two other JE virus strains, S A14/USA and S892, were only neurovirulent. Infectivity titrations of b rains and sera showed that P3 virus multiplied faster and reached a hi gher infectivity titre than S892 virus following inoculation of viruse s by the intraperitoneal (i.p.) route, The p.f.u./LD(50) was 10(1.7) a nd 10(6.2) for P3 and S892 viruses respectively, following i.p. inocul ation, while JE virus strain SA14/USA did not kill mice when inoculate d by this route (i.e. greater than or equal to 10(6.3) p.f.u./LD(50)). Nevertheless, the genomic similarity between P3 virus and strains SA1 4/USA and S892 was more than 97.8% at the nucleotide level and 99% at the amino acid level, Compared with S899 and SA14/USA viruses, P3 viru s had 33 and 21 amino acid differences, respectively, The structural p rotein genes of 83 virus were more divergent than non-structural prote in genes, Nine unique amino acids were found in the envelope protein g ene, None of these amino acid differences were shared with other wild- type JE virus strains, Although we cannot identify the precise molecul ar determinants of virulence of JE virus, there were no unique amino a cids in M, NS1, NS2A, NS3, NS4A and NS4B proteins of P3 virus compared with other wild-type viruses, Therefore, it appears that these protei ns make no significant contribution to the high neuroinvasiveness of P 3 virus, The structural proteins, and non-structural proteins NS2B and NS5 may be involved in increasing neurovirulence and neuroinvasivenes s of P3 virus, P3 virus differed by several nucleotides in the 3' non- coding region while no nucleotide difference was found in the 5' non-c oding region.