Human parainfluenza viruses 3 (hPIV3) are important pathogens, responsible for acute respiratory tract diseases, especially in young children. Information on hPIV3 circulation and their diversity pattern in Russia is limited. The aim of this study was to perform a molecular and genetic characterization of hPIV3 circulating in Saint Petersburg, Russia. From October 2017 to September 2023, 14,704 swabs were screened using real-time reverse transcription-PCR. A phylogenetic analysis of the complete hemagglutinin–neuraminidase (HN) gene was performed. Out of 1334 positive hPIV cases, hPIV3 was the most common subtype. Phylogenetic analysis of the studied and previously published HN sequences revealed four distinct genetic clusters, A, B, C, and D, with Cluster D being first delineated in this study. In addition, two newly subdivided genetic lineages, C5a and C5b, were documented. Phylogenetic analysis revealed that the analyzed Russian strains grouped into Cluster C and D; further subclusters C5a, C5b, C3b, C3e, and C3a. While three strains were classified within cluster D, the majority of isolates fell within subcluster C3a, followed by C5b. Taken together, these findings demonstrate the co-circulation of hPIV3 strains during the study period. This is the first study that describes the genetic and molecular aspects of hPIV3 circulating in Russia. Moreover, our results provide an up-to-date hPIV3 phylogenetic analysis.

Human parainfluenza viruses (hPIVs) are major contributors to respiratory tract infections in young children worldwide. Despite their global significance, genomic surveillance of hPIV1 and hPIV2 had not previously been conducted in Russia. This study aimed to develop a robust amplicon-based sequencing protocol for these viruses. The designed primer sets were tested on clinical samples containing hPIV RNA to evaluate their performance and efficiency. Sequencing results demonstrated high-quality genome data and efficient amplification across various Ct values. As a result, 41 hPIV1 and 13 hPIV2 near-complete genome sequences were successfully obtained from clinical specimens collected in Saint Petersburg (Russia). Phylogenetic analysis of the HN gene sequences showed that Russian hPIV1 strains clustered into clades II and III, while hPIV2 strains were distributed between clusters G1a and G3. The whole-genome-based trees confirmed the same distribution of the strains. These findings highlight the potential of our primer panels and contribute to a better understanding of the molecular characteristics and phylogenetic diversity of circulating hPIV strains. Notably, this study presents the first evolutionary analysis of hPIVs in Russia.

Human parainfluenza virus type 4 (hPIV4) remains poorly characterized compared with other hPIV serotypes and information on its genomic diversity is particularly limited for Russia and Eastern Europe. In this study, we report the first complete genome sequences of hPIV4 isolates from Russia and place them in the context of global hPIV4 genetic diversity. Eight hPIV4 viruses were isolated in cell culture from respiratory samples collected from hospitalized children in Saint Petersburg between 2017/2018 and 2023/2024. Complete viral genomes were recovered using a metagenomic whole-genome amplification approach based on SMART-9N technology. Phylogenetic analysis of 178 complete hPIV4 genomes showed clear separation into hPIV4a (n = 132) and hPIV4b (n = 46) subtypes. Based on genetic distance approach, hPIV4a formed two major clusters, with the dominant cluster B subdivided into four subclusters (B1–B4); and subcluster B4 further resolved into four genetic lineages. All Russian isolates belonged to the subcluster B4 and were distributed among multiple co-circulating lineages. In contrast, hPIV4b genomes segregated into three distinct clusters, reflecting structured genetic diversity within the subtype. Collectively, this study provides, to the best of our knowledge, the first p-distance-based framework for hPIV4 whole-genome classification and contributes new complete genome sequences for an underrepresented region.