Cross-sectional entomological data reveals an increased risk of arboviral transmission in a year of record-breaking heat in Southern Europe.

Background: In 2023, an unprecedentedly high number of locally acquired cases of dengue virus occurred in Europe, including the first large outbreak in Rome (Italy). Globally, 2023 was warmer than any previous year on record since 1850, with each month from June to December being warmer than the corresponding month in previous years.

Methods: We conducted an extensive analysis of entomological data in Rome to investigate how the unprecedentedly high temperatures seen in 2023 affected the abundance and seasonal dynamics of the local vector Aedes albopictus population and the risk of autochthonous transmission of both dengue and chikungunya viruses. We applied a mathematical dynamic temperature-based model to analyse adult mosquito collections in 2023 compared to those available for 2012 and assess the consequent changes in the risk of arboviral transmission. Simulations of potential local transmission triggered by disease importation were used to evaluate the effectiveness of human and entomological surveillance for monitoring transmission risks, providing insights for future action plans RESULTS: Results highlight a higher abundance and longer active season of Ae. albopictus as well as a higher risk of local arbovirus transmission in 2023.

Conclusions: Our findings raise concern in light of the predictions for more frequent extremely warm years in Europe in the near future.