Temporal genetic changes in human bocavirus 1 in Fukushima, Japan, from 2018 to 2024.

Introduction. Human bocavirus 1 (HBoV1) is a member of Bocaparvovirus primate1 and is associated with paediatric respiratory infections. Although genetic grouping has been described, it remains unclear whether temporal genetic changes occur among clinically circulating HBoV1 strains.Hypothesis/Gap Statement. HBoV1 shows limited genetic diversity, but temporal genetic changes may occur in circulating strains.Aim. To investigate whether temporal genetic changes are present in HBoV1 isolates collected in Fukushima, Japan, between 2018 and 2024.Methodology. Nasopharyngeal swabs were collected from paediatric inpatients with acute respiratory infections. Thirty-two HBoV1 isolates were obtained using air-liquid interface cultures of human bronchial/tracheal epithelial cells. Nearly complete genomes were sequenced by next-generation sequencing and analysed together with additional reference sequences (total n=100, including outgroups) using phylogenetic and time-scaled methods.Results. Phylogenetic analyses classified the 32 Fukushima isolates into Group 1 (n=12) and Group 2 (n=20). Group 2 predominated in 2018, Group 1 from 2019 to 2021 and Group 2 again from 2022 to 2024, indicating temporal shifts in circulating strains. The average number of nucleotide differences among HBoV1 genomes was 13.9 (maximum 55), with Groups 1 and 2 diverging around 2004-2005. Divergence was concentrated in the VP genes, and synonymous substitutions within VP genes overlapped the ORFx reading frame, leading to distinct amino acid differences in ORFx.Conclusion. Clinically circulating HBoV1 undergoes temporal genetic change, with group differentiation determined primarily by VP genes and uniquely by ORFx at the amino acid level. These findings suggest a potential biological role for ORFx in the HBoV1 life cycle. Understanding these temporal genetic shifts is important for enhancing the accuracy of molecular surveillance tools, particularly for distinguishing genetically diverse HBoV1 strains.