Parechovirus A3 Infections, Including Myalgia, in Yamagata, Japan, Between 2022 and 2023 and Their Next-Generation Sequencing Analyses.

Since we reported the first parechovirus A3-associated myalgia (PeVA3-M) outbreak in Yamagata in 2008 as an emerging disease, we have investigated PeVA3 infections as part of the National Epidemiological Surveillance of Infectious Diseases, Japan, in sentinel hospitals and clinics and also performed a specific symptomatic surveillance targeting PeVA3-M. As PeVA3-M has only been reported from Japan, it is necessary to continue the above surveillance. In our surveillance from July 2022 to December 2023, we found 31 PeVA3 infections, including three confirmed or suspected PeVA3-M cases, using PCR and a virus isolation method. Further next-generation sequencing (NGS) analysis was performed for the representative isolates and their original specimens between 2022 and 2023 as well as those between 2003 and 2019. NGS analysis showed that 7,245-7,309 and 7,118-7,287 nucleotides (98.7%-99.8% and 97.1%-99.4% compared with the reference strains) were available from 25 representative isolates and from 6 clinical specimens, respectively. This study indicated that the recombinant PeVA3 strains, which appeared in 2019, remained in circulation in Yamagata between 2022 and 2023. Furthermore, the NGS method is useful for the molecular epidemiological surveillance of PeVA3 infections, although improvements in the method used for the clinical specimens are required.