Figure 4.

Continued evolution and genetic variation of North American WNV isolates, 1999–2012. North American WNV isolates (n = 454) published in GenBank between 1999–2012 were compared to the prototype NY99-flamingo382-99 isolate (NY99, AF196835) [32] to determine the average annual percent (%) nucleotide divergence (black dots). Error bars indicate standard error from mean values. Red dotted lines, respective minimum and maximum annual % nucleotide divergence from NY99. Evaluation of overall annual WNV diversity (black line) is demonstrated as the maximum annual % nucleotide divergence between all published virus sequences. Estimates for 2012 included isolates from the 2012 Texas epidemic alone [45,56].