A systematic review of environmental factors related to WNV circulation in European and Mediterranean countries

INTRODUCTION/OBJECTIVE: West Nile virus (WNV) is one of the most widely distributed flaviviruses worldwide. It is considered an endemic and emerging pathogen in different areas of the Europe and Mediterranean countries (MR). Mosquitoes of the genus Culex spp. are the main vectors, and birds its main vertebrate hosts. It can occasionally infect mammals, including humans. Different environmental factors can influence its distribution and transmission through its effects on vector or host populations. Our objective was to determine environmental factors associated with changes in vector distribution and WNV transmission in Europe and MR. MATERIAL & METHODS: Systematic peer review of articles published between 2000 and 2020. We selected studies on WNV, and its vectors carried out in Europe and MR. The search included terms referring to climatic and environmental factors. RESULTS: We included 65 studies, of which 21 (32%) were conducted in Italy. Culex spp. was studied in 26 papers (40%), humans in 19 papers (29%) and host animals (mainly horses) in 16 papers (25%), whereas bird reservoirs were addressed in 5 studies (8%). A significant positive relationship was observed between changes in temperature and precipitation patterns and the epidemiology of WNV, although contrasting results were found among studies. Other factors positively related to WNV dynamics were the normalized difference vegetation index (NDVI] and expansion of anthropized habitats. CONCLUSION: The epidemiology of WNV seems to be related to climatic factors that are changing globally due to ongoing climate change. Unfortunately, the complete zoonotic cycle was not analyzed in most papers, making it difficult to determine the independent impact of environment on the different components of the transmission cycle. Given the current expansion and endemicity of WNV in the area, it is important to adopt holistic approaches to understand WNV epidemiology and to improve WNV surveillance and control.