Epidemiological characteristics and viral molecular evolution analysis of severe fever with thrombocytopenia syndrome in Shandong Province, China

Characterized by a high mortality rate and a widening global distribution, severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne emerging infectious disease spawned from the Bandavirus dabieense (DBV). Shandong Province emerges as one of the predominant endemic areas for SFTS in China. On the account, this research probed into the epidemiological characteristics of SFTS in Shandong in 2024. On this basis, this study revealed the genetic evolutionary features and genotype distribution of locally circulating DBV strains through whole-genome sequencing (WGS) and phylogenetic analysis. SFTS cases were mainly reported during spring and summer, peaking from May to August. The majority of cases (1569/1656, 94.7 %) were over 50 years old, and the majority were farmers (1368/1656, 82.6 %). This phenomenon sufficiently underscores its high-risk populations. As demonstrated by viral genome analysis, DBV in Shandong Province is classified into three genotypes (A, B, and C). It is particularly noteworthy that genotype B plays a dominant role. Aside from that, 7 reassortant types and 11 recombination events were identified. Across four open reading frames (ORFs) of DBV, 222 mutation sites were detected, with GP and NSs exhibiting higher mutation frequencies. As the selection pressure analysis suggested, all four ORFs were subject to purifying selection. To conclude, the SFTS epidemic in Shandong Province exhibits distinct seasonal and demographic characteristics. DBV isolates demonstrate the complex genetic diversity and evolutionary dynamics, which adequately underline the pressing demand for ongoing surveillance to track viral evolution and inform prevention strategies.