West Nile Virus Strains Differ in Mouse Neurovirulence and Binding to Mouse or Human Brain Membrane Receptor Preparations

The recent introduction of West Nile (WN) virus into the Western Hemisphere has focused considerable attention on this virus as a public health problem. As a result, there have been considerable advances in our knowledge of the molecular biology and phylogeny of WN virus strains from different geographical origins. However, relatively little is known about the virulence phenotypes of these viruses. Human infections with WN virus generally result in a mild, self-limiting, undifferentiated fever. However, recent outbreaks in North America and eastern Europe have been associated with a relatively high percentage (up to 10%) of cases involving potentially fatal neurological manifestations.1 The aim of this study was to systematically compare 19 strains of WN virus (TABLE 1) to determine whether biological differences exist between them that can be correlated with genotype. To facilitate this, we undertook a series of mouse neurovirulence experiments, and compared the ability of these viruses to bind to mouse and human brain tissue membrane receptor preparations (MRPs). In addition, we sequenced a ~500 bp region of the NS5 gene/3′-noncoding region (NCR) junction for comparison with other phylogenetic analyses that used segments of the E protein gene. Viruses were chosen to represent each of the known WN virus lineages: lineage I (primarily European and Middle Eastern isolates, but also isolates from the 1999 New York outbreak and some African isolates); lineage II (which comprises African isolates only); Kunjin (KUN) viruses; and Indian WN virus isolates (antigenically distinct from both lineages I and II).2,3 As has been reported previously with a smaller group of WN viruses,3 considerable variation was observed in the region of the 3′-NCR immediately following the