Abstract
In this study, we investigated the antigenic and genetic characteristics of influenza viruses circulating in Bulgaria during the 2017/2018 season. The detection and typing/subtyping of influenza viruses were performed using real-time RT-PCR. Results of antigenic characterisation, phylogenetic and amino acid sequence analyses of representative influenza strains are presented. The season was characterised by the predominance of B/Yamagata viruses, accounting for 77% of detected influenza viruses, followed by A(H1N1)pdm09 (17%), B/Victoria (3.7%) and A(H3N2) (2.4%). The sequenced B/Yamagata, B/Victoria, A(H1N1)pdm09 and A(H3N2) viruses belonged to the genetic groups 3, 1A, 6B.1 and 3C.2a1, respectively. Amino acid analysis of B/Yamagata isolates revealed the presence of three changes in haemagglutinin (HA), eight changes in neuraminidase (NA) and a number of substitutions in internal proteins compared with the B/Phucket/3073/2013 vaccine virus. Despite the amino acid changes, B/Yamagata viruses remained antigenically related to the vaccine strain. B/Victoria isolates fell into a group of viruses with double deletion (Δ162-163) in HA1. Substitutions in HA and NA sequences of B/Victoria, A(H1N1)pdm09 and A(H3N2) viruses were also identified compared with the vaccine strains, including in antigenic sites. The results of this study confirm the genetic variability of circulating influenza viruses and the need for continual antigenic and molecular surveillance.
Highlights
Influenza is a highly contagious viral respiratory infection with the highest impact on population health in the EU/EEA compared with other infectious diseases due to its substantial incidence and associated mortality [1]
In the 2017/2018 season, the influenza epidemic in Bulgaria started in week 1/2018 and continued until week 9/2018
Thirty-nine representative influenza isolates were sent to the WHO Collaborating Centres (WHO-CC), London, where they were characterised in detail
Summary
Influenza is a highly contagious viral respiratory infection with the highest impact on population health in the EU/EEA compared with other infectious diseases due to its substantial incidence and associated mortality [1]. Influenza B viruses are not categorised into subtypes but are divided into two phylogenetically and antigenically distinct lineages (Victoria and Yamagata), which have been co-circulating worldwide in variable proportions since the beginning of the XXI century [3,4,5]. These viruses are almost exclusively human pathogens, affect all age groups, but most commonly school-age children (aged 5–17 years) and in contrast to influenza A viruses do not pose a pandemic threat [6]. Influenza B viruses rarely represent over 50% of influenza cases, but when their activity is intense, they can cause severe epidemics [6, 8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
