West Nile virus in Portugal

West Nile virus (WNV) causes outbreaks with sustained spillover to humans in many European countries. Despite Portugal’s Mediterranean climate being adequate for WNV transmission, only four human infections have been detected there so far. Here, we offer an historical account of past WNV circulation and develop new, climate-driven insights on the geo-temporal suitability for WNV transmission in Portugal. WNV and vector related literature and database reviews were performed in the context of Portugal covering the time period 1966-2020, and local climate data were used to estimate WNV transmission suitability for the period 1981-2019. Reviewed data demonstrate that WNV-compatible vectors are abundant across the entire country, while molecular and serological evidence for WNV circulation has mostly been associated with the southern districts. Our estimated WNV transmission suitability was found to support geographical differences in transmission potential that favour the southern districts, with an increasing trend over the past forty years due to climate change. Empirical and theoretical evidence supports WNV circulation in Portugal, but it remains unclear whether the virus is endemic or sporadically transmitted. Given the recent public health emergencies related to WNV in other European countries and the findings herein described in relation to Portugal, our study supports a timely change towards a local WNV active surveillance.