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. 2024 Apr 2:15:1376389.
doi: 10.3389/fmicb.2024.1376389. eCollection 2024.

Resurgence of respiratory syncytial virus with dominance of RSV-B during the 2022-2023 season

Neli Korsun  1 , Ivelina Trifonova  1 , Iveta Madzharova  1 , Ivaylo Alexiev  1 , Iordanka Uzunova  2 , Ivan Ivanov  3 , Petar Velikov  3 , Tatiana Tcherveniakova  3 , Iva Christova  1
Affiliations

Resurgence of respiratory syncytial virus with dominance of RSV-B during the 2022-2023 season

Neli Korsun et al. Front Microbiol. .

Abstract

Background: Respiratory syncytial virus (RSV) is a common cause of upper and lower respiratory tract infections. This study aimed to explore the prevalence of respiratory syncytial virus (RSV) and other respiratory viruses in Bulgaria, characterize the genetic diversity of RSV strains, and perform amino acid sequence analyses of RSV surface and internal proteins.

Methods: Clinical and epidemiological data and nasopharyngeal swabs were prospectively collected from patients with acute respiratory infections between October 2020 and May 2023. Real-time PCR for 13 respiratory viruses, whole-genome sequencing, phylogenetic, and amino acid analyses were performed.

Results: This study included three epidemic seasons (2020-2021, 2021-2022, and 2022-2023) from week 40 of the previous year to week 20 of the following year. Of the 3,047 patients examined, 1,813 (59.5%) tested positive for at least one viral respiratory pathogen. RSV was the second most detected virus (10.9%) after SARS-CoV-2 (22%). Coinfections between RSV and other respiratory viruses were detected in 68 cases, including 14 with SARS-CoV-2. After two seasons of low circulation, RSV activity increased significantly during the 2022-2023 season. The detection rates of RSV were 3.2, 6.6, and 13.7% in the first, second, and third seasons, respectively. RSV was the most common virus found in children under 5 years old with bronchiolitis (40%) and pneumonia (24.5%). RSV-B drove the 2022-2023 epidemic. Phylogenetic analysis indicated that the sequenced RSV-B strains belonged to the GB5.0.5a and GB5.0.6a genotypes. Amino acid substitutions in the surface and internal proteins, including the F protein antigenic sites were identified compared to the BA prototype strain.

Conclusion: This study revealed a strong resurgence of RSV in the autumn of 2022 after the lifting of anti-COVID-19 measures, the leading role of RSV as a causative agent of serious respiratory illnesses in early childhood, and relatively low genetic diversity in circulating RSV strains.

Keywords: evolution; genetic variability; genotype; molecular epidemiology; respiratory syncytial virus; whole-genome sequencing.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Monthly distribution of respiratory viruses detected among patients with ARI.
Figure 2
Figure 2
Age distribution of patients aged 0–59 months with detected respiratory viruses. Positive cases represent the sum of single infections and co-infections for each virus.
Figure 3
Figure 3
Number of respiratory viruses detected in patients with tracheobronchitis, bronchiolitis, pneumonia, and CNS complications during the 2022–2023 season.
Figure 4
Figure 4
Phylogenetic analysis based on G gene nucleotide sequences of RSV-B strains. A phylogenetic tree was constructed using the maximum-likelihood method with 1,000 bootstrap iterations running within Geneious Prime software. Reference sequences were labeled with GenBank names and accession numbers, followed by country, year of isolation, and genotype. Reference RSV-B strains are indicated in yellow background. GB5.0.5a and GB5.0.6a strains detected during 2022–2023 are indicated in green and purple background, respectively. The names of the reference GB5.0.5a strains are highlighted in blue.
Figure 5
Figure 5
Deduced amino acid alignment of the G protein HVR2 in the RSV-B strains. Alignment is shown relative to the sequence of the prototype BA strain NH1182 (GenBank accession number MF185752). The amino acid numbers correspond to G protein positions 213–312 of strain MF185752. Identical residues are indicated by dots. Outlined rectangles represent two copies of the duplicated 20-amino acid region in the RSV-B strains. Light gray shading highlights the predicted N-glycosylation sites. Black circles indicate the predicted O-glycosylation sites of the BA prototype strain MF185752, and unfilled circles indicate the predicted O-glycosylation sites of the Bulgarian strains.
Figure 6
Figure 6
Location of amino acid substitutions identified in RSV-B F protein. Structural sites of the F protein sequence are shown: SP (signal peptide), F2 subunit (aa 24–109); p27 peptide; FP (fusion peptide); F1 subunit (aa 137–524); HR1 and HR2 (heptad repeats); and TM/CT (transmembrane/carboxy terminus).
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Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This study was supported by grants from the Ministry of Education and Science, Bulgaria (contract: KП-06-H73/7-05.12.2023 and contract: KП-06-H43/5-30.11.2020), and by the European Regional Development Fund through Operational Program Science and Education for Smart Growth 2014–2020, Grant BG05M2OP001-1.002-0001-C04 “Fundamental Translational and Clinical Investigations on Infections and Immunity.”