An intensified and continuous West Nile Virus spread across Northern Italy has been observed since 2008, which caused more than a hundred reported human infections up until 2016, concentrated in two regions, Emilia-Romagna and Veneto. We calibrated, using a Bayesian approach, a mathematical model that simulates WNV infection in an avian population with seasonal demography on entomological data collected in Veneto in those years. We compared two assumptions, that the virus is introduced every year at the beginning of the vector breeding season by either infected birds, migrating to the study area, or by diapausing mosquitoes which were infected the previous year. The results suggest that the infection starts every year in infected mosquitoes, supporting the idea that the virus overwinters in the area. On this basis, we computed seasonal risk curves, indicating the likelihood for a human to be infected, allowing for a temporal shift in vector feeding preferences, according to independent estimates. The highest probability of human infection is estimated for August, consistently with observations. Finally, multi-year simulations show a qualitative agreement with observed patterns. We are currently working at extending the model to the region Emilia-Romagna (where also data on prevalence in shot corvids are available) and on spatial spread. Joint work with Giovanni Marini, Roberto Rosà, Marco Tosato, Caterina Rizzo, Gioia Capelli.