Epidemiological and clinical characteristics of laboratory-confirmed Yezo virus infections in tick-bitten humans in China, 2023–2025: A prospective observational study

Yezo virus (YEZV) is an emerging tick-borne nairovirus first identified in Japan in 2021. Following the initial case in the Daxing’an Mountains (DXAM) of northeastern China, no additional cases were reported until this study. Here, we characterize the epidemiological and clinical features of YEZV infection in the DXAM region and examine the genetic evolution and transmission dynamics of circulating strains. Between April and September 2023–2025, 4,213 individuals with tick bites were enrolled, of whom 16 tested positive for YEZV. All patients presented with fever; headache, cough, gastrointestinal symptoms, and neurological manifestations occurred in 62.5%, 43.8%, 56.3%, and 25.0% of cases, respectively. At admission, 50.0% exhibited abnormal white blood cell counts and 62.5% had elevated aspartate aminotransferase levels. Phylogenetic analysis revealed no distinct geographic clustering of YEZV strains. Three recombination and ten reassortment events were identified, including three involving both Japanese and Chinese strains. These findings demonstrate that YEZV has become endemic in northeastern China and strongly support the implementation of routine YEZV testing in tick-bitten patients within Ixodes persulcatus–endemic regions.