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

OBJECTIVES: To characterize the epidemiological and clinical features of Yezo virus (YEZV) infection in the Daxing'an Mountains (DXAM) region and analyze the genetic evolution and spread patterns of YEZV strains between DXAM and other regions. METHODS: This prospective surveillance study at Inner Mongolia Forestry General Hospital enrolled individuals with recent tick bites from April to September 2023-2025. Serum samples were tested for YEZV infection using RT-qPCR. Epidemiological, clinical, and laboratory data were collected. Positive samples underwent nested PCR for complete YEZV genomes, followed by phylogenetic and recombination analyses. RESULTS: Between April and September 2023-2025, 4213 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. CONCLUSIONS: 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.