Genetic connectivity and admixture zones shape the spread of African swine fever in wild Boar populations in North-western Italy

Host population genetics can shape disease spread in wildlife, yet it is rarely integrated into epizootic investigations. To explore whether connectivity patterns in wild boar populations may have influenced the spread of African swine fever (ASF) in north-western Italy, we characterised the genetic structure of the local population. Microsatellite genotyping was performed on 578 wild boar sampled from 26 hunting districts across thirteen loci and analysed using Bayesian clustering, correspondence analysis and spatial PCA. In parallel, 2,414 ASF detections recorded between December 2021 and March 2025 were examined through retrospective spatiotemporal scan statistics and directional spread analysis. We identified two main genetic clusters, one largely corresponding to Piedmont and the other more prevalent in Liguria regions, with zones of admixture along their border and a connectivity corridor through the Ligurian Apennines. Over the 38-month period, 16 significant ASF clusters were detected. The outbreak spread eastward and north-eastward from the initial focus at the Liguria-Piedmont border. Four clusters showed significant directionality, and recurrent clustering in certain areas suggested local persistence. Notably, several ASF clusters overlapped with genetic admixture zones and connectivity hubs. Our findings suggest two mechanisms underpinning disease spread: short-range transmission within genetically related groups and longer-range movement along ecological corridors. Embedding genetic monitoring into routine surveillance may enhance the effectiveness of ASF control by guiding carcass removal, search efforts and spatial prioritisation toward high-risk transition zones.