Figure 2.

Bayesian coalescent phylogenetic tree depicting the simplified distribution of the North American WNV genotypes within Lineage 1a Cluster 4. Posterior probabilities (≥0.92) support the emergence of at least four unique WNV genotypes and/or clusters in North America from ancestral North African strains: NY99 (red), NA/WN02 (blue), SW/WN03 (green), and MW/WN06 (gold). Both the number and temporal range are indicated for the isolates which cluster within each genotype or cluster. Scale bar, divergence time in years.