Meteorological and environmental drivers of West Nile virus prevalence in Culex pipiens mosquitoes in Emilia-Romagna, Italy in 2013 to 2022

As West Nile Virus (WNV) is expanding its geographical range across Europe, there is an urgent need to characterise and better understand its transmission drivers to inform public health surveillance, disease control, and preparedness planning. We utilised 10 consecutive years of large-scale and fine-resolution WNV entomological field surveillance data from the Emilia-Romagna region in northern Italy, to evaluate the relationships between WNV infection rates in Culex mosquitoes and environmental and climatic conditions as well as WNV presence in the avian reservoir. We used fine-scale spatiotemporal regression models including non-linearities, to assess the drivers of presence and prevalence of WNV-positive mosquitoes. We validated the model estimates against reported cases of human WNV neuroinvasive disease in the region. We found evidence of established hotspots of mosquito WNV infection across multiple years. The presence of WNV in local birds was positively associated with presence and prevalence of WNV-positive mosquitoes (mean regression coefficients: 0.776 (95% CrI, 0.469, 1.08) and 0.226 (95% CrI, 0.053, 0.399) respectively), and the proportion of agricultural land use was positively associated with presence of WNV-positive mosquitoes (4.20 (95% CrI, 2.65, 5.75)). We identified a minimum temperature threshold around 13°C, below which mosquito WNV infection was reduced. Our findings provide evidence of the impact of temperature and environment on Culex populations and WNV infection dynamics at the local level, which were highly correlated with human case reports. The estimated role of the minimum temperature and the observed and projected increase in this variable under climate change suggest that WNV will continue to represent a risk for human and animal health in the region in future decades. Future work should focus on better understanding the mechanisms behind infection drivers, on the optimal implementation of surveillance and control activities around high-risk areas, and on the assessment of how specific land use practices could represent potential solutions to WNV infection.