Continued Evolution of West Nile Virus, Houston, Texas, USA, 2002–2012
Figure 2. . Incidence of vector-borne West Nile Virus (WNV) in Harris County, Texas, USA, 2002–2012, showing cumulative distribution of confirmed avian and mosquito (Culex and Aedes spp.) WNV isolates. Small numbers indicate reference codes for each of the 268 mosquito control operational areas. Black open symbols indicate 2002–2009 group 1–6 mosquito (circles) and bird (squares) isolates collected in mosquito control operational areas. Colored solid symbols indicate 2002–2012 Harris County isolates that cluster within monophyletic group 7 (red), group 8 (blue), group 9 (green), or group 10 (gold). Black solid symbols indicate nonclustering 2012 TX8572 and TX8604 isolates within groups 1–10. Not shown are TX 2002 1, TX 2002 2, TX 2003, and TX1461. IH, interstate highway.