West Nile Virus in Italy: An Update of the Viral Strains Circulating in the Late 2022 Epidemic Season.

Simple Summary: West Nile virus (WNV) infection is a significant public health concern in Europe and Italy is one of the most affected countries since 2008. This brief report describes circulation cases of West Nile virus lineage 1 and lineage 2 strains occurring at the end of the 2022 vector season in Sicily and Tuscany, regions where no strains had ever been sequenced. The genetic characterization of the WNV strains responsible for these cases confirmed the peculiar WNV Italian scenario, marked by endemic Italian circulation spreading to new areas of the country (Tuscany case) and novel introductions from different European and Italian areas (Sicilian episode). It highlights the importance of continuous molecular surveillance for the early detection of viral circulation throughout the country and the monitoring of the arrival of new strains and the evolution of novel variants, in order to trigger adequate measures and limit its spread and human infections. West Nile virus (WNV) (Flaviviridae, Flavivirus) infection is a mosquito-borne zoonosis able of causing disease and death in humans and animals. Over the past decade, WNV infections have been a significant public health concern in Europe, and Italy has been among the most affected countries since 2008. The 2022 vector season has been characterized by an intense and early circulation of WNV. This report describes cases of co-circulation of WNV L1 and of WNV L2 occurring at the end of the 2022 vector season in Sicily and Tuscany, regions where no strains had ever been sequenced. The phylogenetic analysis of the detected strains confirmed the peculiar WNV scenario that has characterized the Italian West Nile disease (WND) epidemic since its appearance. The circulation observed in Tuscany was in fact a consequence of the spread of endemic strains to new areas while the Sicilian episodes were linked to new introductions of WNV L1 and L2 strains likely from other European countries. [ABSTRACT FROM AUTHOR]