Spatial Analysis of West Nile Virus in the United States: Distribution of Culex tarsalis and Efficacy of Vector Control

Abstract

West Nile virus (WNV), is a flavivirus primarily vectored by Culex mosquitoes. As the primary mosquito-borne disease in the United States, WNV has had case reports every year since its introduction in 1999 and is widespread across the United States. Considering its widespread importance, it is critical that we characterize the distribution of vectors and evaluate vector control measures. Estimations of species distributions for Culex tarsalis, a major WNV vector, are extremely limited. We use an ensemble approach to species distribution modeling to estimate habitat suitability across the contiguous United States. The central plains region and much of the western U.S. were estimated to have high habitat suitability. We also found multiple metrics of temperature and precipitation to be important in predicting the occurrence of Cx. tarsalis in a given geographic area.

We also evaluated the efficacy of Harris County’s truck-based adulticide program. Since its introduction in 2002, WNV has been reported annually in Harris County, Texas. To mitigate transmission, the Harris County Public Health Mosquito and Vector Control Division (HCPH MVCD) routinely conducts truck-based adulticide spraying. Previous studies in Harris County have investigated insecticide resistance in mosquitoes, compared resistance to different insecticide classes, and evaluated different forms of vector surveillance. However, long-term efficacy of adulticide applications has not been evaluated. This study utilizes a time series analysis to characterize the monthly and weekly influence of adulticide application on Culex quinquefasciatus abundance and WNV infection over an eighteen-year period. We observe no clear effects of adulticide application on Culex abundance, but we do note a long term negative association between adulticide application and infection with WNV. Further studies should investigate the efficacy of truck or arial application of adulticide for the management of WNV.