Genomic characteristics of 12 HBV-I strains in the 2020 national HBV serosurvey in China.

Hepatitis B virus (HBV) is categorized into ten distinct genotypes (A - J), with over 40 subgenotypes identified to date. HBV genotype I (HBV-I), an inter-genotypic recombinant, has emerged during the evolution history of HBV. In this study, we conducted a comprehensive analysis of the genomic characteristics of HBV-I in China, employing a range of methodologies including phylogenetic analysis, nucleotide homology assessment, examination of amino acid substitutions within the PreS/S region, recombination detection, and evolutionary analysis. The 12 HBV-I strains, classified into subgenotype I1 and predominantly serotype adw2 (with one exception being ayw1) were preliminarily divided into two clusters based on homology analysis. A higher substitution rate was observed in the antigenic loop of the hepatitis B surface antigen (HBsAg), and the potential immune-escape mutations were found. Molecular clock analysis estimated an average evolutionary rate for HBV-I between 1.17 exp(-4) and 1.61 exp(-4) substitutions/site/year, with the most recent common ancestor traced back to between year 1740 and 1774. The epidemiological surveillance and genomic characterization of HBV genotype I are significant for informing future strategies in the prevention and control of hepatitis B.