Advancing West Nile virus monitoring through whole genome sequencing: Insights from a One Health genomic surveillance study in Romagna (Italy)

In the last 6 years, Italy accounted for 36 % of the total autochthonous European West Nile virus (WNV) cases reported to ECDC. Since 2001, the country put in place a multi-species national surveillance plan. The plan was enhanced in 2020 by adopting a fully integrated "One Health" approach, including human, wild bird, equine, and mosquito surveillance for the early detection of WNV. In this context, the systematic acquisition of whole viral genetic information from human patients and animals is fundamental to obtain an in-depth knowledge on the patterns of virus evolution and transmission and to gain insights on the role virus genetics in morbidity and mortality, The purpose of this pilot study was thus to design a One-Health surveillance framework based on the genomic surveillance of WNV circulating at the vector-human-animal interface, in the endemic territory of Romagna (North-Eastern Italy) during the 2023 transmission season. Whole genome sequencing (WGS) analyses confirmed the circulation of WNV lineage 2 showing high nucleotide and amino acid identity of 99.82 % and 99.92 % respectively among viral sequences from human patients, vectors and birds. All the sequences clustered with other Italian strains in the Central and Southern European clade with robust bootstrap support and BLASTn identity exceeding 99.7 %. The highest nucleotide identity was observed with sequences from Emilia-Romagna and Veneto regions (Italy), confirming a local virus circulation and overwintering of WNV lineage 2 with a confined virus spread and no (or limited) external introduction of viral strains. Our results, support the adoption of a One Health approach to WNV surveillance, based on WGS and integrating the clinical diagnosis, epidemiology, and genomic characterisation, to create a suitable operational process for the characterisation of autochthonous and imported Arboviruses circulating in Romagna to effectively integrate the already established surveillance plan.