Scenario-driven shifts in future Usutu and West Nile virus outbreak characteristics in the Netherlands.

Mosquito-borne virus transmission is shaped by its ecological context, including land use, climate, and population dynamics. Future changes in these factors may therefore affect the risk and intensity of Usutu virus (USUV) and West Nile virus (WNV) outbreaks in the Netherlands. We compared a reference scenario to four future Shared Socio-economic Pathway scenarios developed for the Netherlands, which differed in land use, host distribution, mosquito distribution, and temperature. Temperature (between + 1.0 °C and + 1.7 °C) and mosquito abundance (between + 5% and + 10%) were predicted to increase during the transmission season across the scenarios. Scenario effects on hosts differed between species with the largest abundance increases predicted for WNV hosts. We found that outbreak size and growth rate were expected to increase in all future scenarios for both USUV and WNV. These effects were most pronounced early in the season and in scenarios characterised by a high temperature increase. Changes in outbreak risk differed between locations due to spatial variation in changes in host and vector abundance, but risk generally increased most in Southern and Eastern regions. Across a range of possible future scenarios, USUV and WNV outbreaks are expected to become larger, grow faster, and last longer. This is mostly driven by increased temperatures, highlighting the importance of climate mitigation measures to reduce disease outbreak risk and impact.