Molecular evolution and geographic migration of severe fever with thrombocytopenia syndrome virus in Asia

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a recently identified tick-borne virus that has emerged in the twenty-first century. Its primary clinical manifestations include fever and thrombocytopenia, and its high morbidity and mortality rates have garnered significant attention. It is crucial to have a comprehensive understanding of the spatial and temporal characteristics of SFTSV migration in order to prevent and control this disease. The SFTSV strains from East Asian countries in GenBank during 2017-2023 were collected and analyzed with phylogenetic and Bayesian methods. Phylogenetic analysis showed that SFTSV can be categorized into five genotypes (A, B, C, D, and E), with 24 recombination events and 15 reassortment events identified. This represented a higher number than previously observed. The results of our study indicated that SFTSV first diverged around 1785. We categorized the migration of SFTSV into two distinct periods, and identified the centers of spread and migration routes of SFTSV in each period. We propose that the eastern migration routes of migratory birds played a pivotal role during the initial stages of virus transmission, functioning as a primary conduit for the dispersal of the virus across the sea. The eastern and central migratory routes were similarly pivotal in subsequent phases of virus transmission. The results of the study showed that Japan was the first region where the virus originated and became endemic, and that the virus spread widely among countries. Elucidating the spatial and temporal characteristics of SFTSV migration will help prevent and control SFTS.