7. Geospatial Analysis of West Nile Virus (WNV) Incidences in a Heterogeneous Urban Environment: A Case Study in the Twin Cities Metropolitan Area of Minnesota

West Nile virus (WNV) infected dead bird sites and human cases are frequently located in the densely populated, urban areas primarily because they are reported by people. However, the spatial pattern (i.e. morphology) of the urban landscape features could also contribute to the location of WNV incidences. This study has two objectives: (1) analyzing the association of urban environmental features that facilitated the viral activities of WNV infection in the TCMA from 2002 to 2007 and (2) comparing the spatial association between WNV infected mosquito pools and human cases with heterogeneous urban characteristics. It also addresses the question of how urban morphology affects human health. Using a combination of factorial ecology, geospatial techniques, and hierarchical cluster analysis, urban landscape classes are derived from the environmental and built environment risk-factors hypothesized to be associated with WNV transmission. The infection rate among, birds, mosquitoes, and human cases are then compared to these urban classes. Results indicate that the WNV infection rate is considerably higher in the urban class located just outside the cities of Minneapolis and Saint Paul. The dominant features of this class are close proximity to bogs and swamps, parks, sewerage system, waste water discharge sites, trails, high density of catch basins, moderate density of single family houses, and medium vegetation cover with stagnant waters. In general, the rate of infection decreases with increasing distance from the urban core. This is critical, in terms of vector control policies, because two out of four WNV carrying vectors, Culex restuans and Culex pipiens are predominantly urban mosquitoes.