The relationships between West Nile and Kunjin Viruses

Until recently, West Nile (WN) and Kunjin (KUN) viruses were classified as distinct types in the Flavivirus genus. However, genetic and antigenic stud ies on isolates of these two viruses indicate that the relationship between them is more complex. To better define this relationship, we performed seq uence analyses on 32 isolates of KUN virus and 28 isolates of WN virus from different geographic areas, including a WN isolate from the recent outbrea k in New York. Sequence comparisons showed that the KUN virus isolates from Australia were tightly grouped but that the WN virus isolates exhibited su bstantial divergence and could be differentiated into four district groups. KUN virus isolates from Australia were antigenically homologous and distin ct from the WN isolates and a Malaysian KUN virus. Our results suggest that KUN and WN viruses comprise a group of closely related viruses that can be differentiated into subgroups on the basis of genetic and antigenic analys es.