A geospatial analysis of West Nile virus in the Twin Cities metropolitan area of Minnesota.

Abstract

The West Nile virus (WNV) is an infectious disease transmitted to humans and other mammals by mosquitoes that acquire the virus by feeding on WNV-infected birds. Since its initial occurrence in New York in 1999, the virus has spread rapidly west and south, causing seasonal epidemics and illness among thousands of birds, animals, and humans. Yet, we only have a rudimentary understanding of how the mosquito-borne virus operates in complex avian-human-environmental systems. The virus first reached Minnesota in 2002 and resulted in several hotspots by 2003. The year 2007 saw one of the severest incidences of WNV in Minnesota. For my dissertation research, I have developed novel approaches to understand the spread and dynamics of the virus by using key environmental, built environment, and anthropogenic risk factors that determine why, when, and where WNV strikes in the Twin Cities Metropolitan area (TCMA). The first study demonstrates the use of a novel spatiotemporal approach to identify exposure areas. The method retrospectively delineates transmission cycles as exposure areas in their entirety, involving dead birds, mosquito pools, and human cases. Given the strong spatial clustering of WNV infections in the urban areas of TCMA, the next study explores how urban landscape features contributed to the viral activities. This investigation contributed to the broader research question in the field of health geography, of how the heterogeneous urban landscape affects human health and disease patterns. The remaining studies focus on the building and interpreting a nonlinear model which captures the complex relationships between the disease incidences and the hypothesized risk factors. The goal of these studies is to identify risk factor(s) whose management would result in effective disease prevention and containment. This dissertation has applied contributions to the vector control policies. The findings from the studies can answer two fundamental questions to eliminate larva and adult mosquitoes capable of carrying WNV. First, when is the optimal time to apply insecticides and pesticides? Second, where (area) should we target spraying of pesticides? This will lead to efficient allocation of resources and allow a balance between mosquito eradication and environmental conservation efforts with respect to insecticide usage.