Identification of climatic factors affecting the epidemiology of humanwest nile virus infections in northern Greece

Abstract

Climate can affect the geographic and seasonal patterns of vector-borne disease incidence such asWest Nile Virus (WNV) infections. We explore the association between climatic factors and the occurrence of West Nile fever (WNF) orWest Nile neuro-invasive disease (WNND) in humans in NorthernGreece over the years 2010-2014. Time series over a period of 30 years (1979-2008) of climatic data of air temperature, relative humidity, soil temperature, volumetric soil water content, wind speed, and precipitation representing average climate were obtained utilising the ECMWF's (European Centre for Medium-Range Weather Forecasts) Re-Analysis (ERA-Interim)system allowing for a homogeneous set of data in time and space. We analysed data of reportedhuman cases of WNF/WNND and Culex mosquitoes in NorthernGreece. Quantitative assessment resulted in identifying associations between the above climatic variables and reportedhuman cases of WNF/WNND. A substantial fraction of the cases was linked to the upper percentiles of the distribution of air and soil temperature for the period 1979-2008 and the lower percentiles of relative humidity and soil water content. A statistically relevant relationship between the mean weekly value climatic anomalies of wind speed (negative association), relative humidity (negative association) and air temperature (positive association) over 30 years, and reportedhuman cases of WNF/WNND during the period 2010-2014 could be shown. A negative association between the presence of WNV infected Culex mosquitoes and wind speed could be identified. The statistically significant associations could also be confirmedfor the week the WNF/WNND human cases appear and when a time lag of up to three weeks was considered. Similar statistically significant associations were identified with the weekly anomalies of the maximum and minimum values of the above climatic factors. Utilising the ERA-Interim re-analysis methodology it could be shown that besides air temperature, climatic factors such as soil temperature, relative humidity, soil water content and wind speed may affect the epidemiology of WNV. © 2016 Stilianakis et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.