Spatiotemporal approaches to map West Nile Virus high-risk exposure areas at local scales using Geographic Information Science technologies

Background: The West Nile Virus (WNV) is an infectious disease transmitted to humans by infected mosquitoes that acquire the virus by feeding on WNV-infected birds. It is spreading rapidly throughout the United States, exacting a high toll in terms of human and animal life. Yet, we only have limited methodologies to delineate high-risk exposure areas to assist intervention design.

Objectives: The objective was to develop methodologies that incorporated space-time interactions of components of the WNV transmission cycle to identify high-risk exposure areas at local scales.

Methods: I developed two novel GIS-based approaches. The first method, ‘Nearest-Neighbor-Distance-Time' (NNDT), was based on calculated distance thresholds among the spatial location of infected birds, mosquito pools, and humans, and also the time required for the virus to be transmitted among them in the cycle. The second method, ‘COMPOSITE', created an overlay map of density estimation and spatiotemporal clustering of each of the components and allowed visualizing the high-risk exposure areas on micro scales. I situated this research in Minnesota though it can be applied to other areas.

Results: The NNDT method identified localized WNV exposure areas within an area ranging from 5 to 75 square miles. The years 2002 and 2003 had three such WNV cycles, followed by one, two, and four in 2004, 2005, and 2006 respectively. The COMPOSITE method also located several high-risk areas. In 2004 and 2006, the NNDT and COMPOSITE method identified two high-risk areas at exact locations near the North and South St. Paul region.

Conclusion: The NNDT and the COMPOSITE methodologies can be used to update mosquito abatement policies, especially in determining the area and the optimal time to apply insecticides in the delineated high-risk areas. This would prevent human exposure to WNV as well as protect the environment from unwarranted use of insecticides in non-risk areas.