Examining the Impact of Tropical Cyclone Events on Human West Nile Virus Cases in Louisiana

Climatic drivers such as temperature and precipitation can influence the spatial and temporal distributions of disease vectors and hosts, thus affecting transmission patterns of mosquito-borne diseases such as West Nile virus (WNV). Extreme weather events like tropical cyclones are another environmental factor that can influence transmission, and storm data could improve the accuracy of models that forecast future WNV outbreaks. Within the United States, WNV is endemic and the leading mosquito-borne disease. Louisiana is a major hotspot of human WNV cases and is also greatly impacted by tropical cyclones. Understanding the environmental factors that trigger WNV outbreaks can inform mosquito control efforts by warning of future periods of elevated disease risk.

This research aimed to assess the influence of tropical cyclones on human WNV cases. Statistical models were developed to quantify historical human cases as a function of distributed lag summaries of environmental indicators of air temperature, humidity, precipitation, and tropical cyclones. Data for this study were derived from three sources: 1) human WNV cases acquired from Louisiana's Department of Health, 2) GridMET meteorological data derived from the NASA North American Land Data Assimilation System, and 3) tropical cyclone data from the NOAA National Centers for Environmental Information Storm Events Database.

A preliminary investigation examined seasonal patterns of tropical cyclones and WNV transmission from 2004-2021. WNV cases normally began in June, peaked in early August, and tapered off in September and October. Due to Louisiana's warm climate, WNV cases often extend into November and December. Tropical cyclones in this area tend to occur over a June-to-November period with their peak in August and September. Therefore, in most years WNV transmission starts to decline before the onset of the tropical cyclone season. We hypothesize that human WNV incidence would increase when a tropical cyclone occurs before August when mosquito populations are increasing and WNV is being amplified in mosquitoes and birds. Conversely, disease risk would be reduced if a tropical cyclone occurs after the peak of human WNV cases in August when temperatures fall and mosquito activity decreases.