Maximum likelihood phylogenetic tree of 21 complete genomes of WNV. Viruses are grouped according to four described lineages of WNV (excluding the lineage 5 Indian group) and the genetic residue at each NS3-249 site is indicated. The three independent emergences of the NS3-249P genotype has been denoted on the tree. In each case an NS3-249Pro genotype emerged (designated in bold black) from a predecessor genotype (Thr; designated in grey). The asterisks represent nodes with bootstrap support values > 95%.