Replication and gene function in Kunjin virus.

Abstract

Kunjin virus has for many years provided a useful model system for study of replication of Flaviviruses. A very close antigenic relationship between KUN virus strain MRM61C and West Nile (WN) virus strain Sarafend, both within the Japanese encephalitis (JE) virus antigenic group, was established previously by plaque neutralization tests (Westaway 1965), and by haemagglutination-inhibition tests in which IgM antibodies were required for specific diagnosis (Westaway 1968). KUN virus is distributed widely throughout Australia (see chapter by Hall et al., this volume) but in contrast to WN virus, it is very rarely isolated from man or associated with severe disease, and the genetic variation among many KUN virus isolates in Australia was estimated to be only about 1% (Mackenzie et al. 1994). The original sequence comparisons between KUN virus and WN virus (Wengler or Nigeria strain) indicated 79% nucleotide homology with 93% homology for deduced amino acid sequences (Cola et al. 1988). These data were adequate for separate Flavivirus species identity either according to the criterion specifying no more than 84% nucleotide sequence identity (Kuno et al. 1998) or by phylogenetic analysis of the amino acid sequences of NS5, the most conserved product (see Westaway and Blox 1997). However, the recent nucleotide sequence analysis of the WN virus New York (WN-NY99) strains involved in the 1999 epidemic of encephalitis in New York City established a very close phylogenetic relationship with KUN virus, especially in the highly conserved NS3 (99% amino acid identity) and NS5 genes (98.8% identity) (Jia et al. 1999; Lanciotti et al. 1999).