Features 2016-2018 Current Human Influenza A(H3n2) Viruses Circulating In Russia

Influenza A(H3N2) viruses demonstrate the highest level of evolutionary variability compared to other influenza viruses circulating in human population. The strains of this subtype affect a large number of people belonging to high-risk groups: children under three years of age, pregnant women, people over 65 years, medical professionals, and persons with chronic nervous, cardiovascular and respiratory diseases. Influenza A(H3N2) viruses result in high mortality rate in subjects over 65 years causing the most severe course, accompanied by serious complications. Here, we present the data on analyzing antigenic and biological properties of human influenza A(H3N2) viruses which circulated in 2016-2018 epidemic seasons in Russia. The data on the neuraminidase activity (MUNANA test) of recent influenza A(H3N2) viruses isolated on MDCK and MDCK-Siatl cell cultures are presented to compare with NA sequencing data in order to assess possible influence of the isolation system on NA activity. Due to changes in virus receptor properties, a choice of optimal isolation conditions is of high importance. The WHO recommended cell cultures differing in receptor properties were used. Efficiency of virus isolation on MDCK and MDCK-Siatl cell lines was also analyzed. It has been established that the efficiency of influenza A(H3N2) virus isolation in MDCK-Siatl cell culture was 77.3%, whereas in MDCK - 71.3%. It was shown that the majority of isolated strains (68.6% in 2016-2017 and 44.6% in 2017-2018) exhibited a NA-induced erythrocyte agglutination. It was found that current A(H3N2) strains isolated in Russia displayed no significant antigenic differences regardless of cell cultures used; however, adaptive substitutions in neuraminidase may emerge. While studying antigenic properties of influenza A(H3N2) viruses by using the HI assay and the microneutralization assay (cell-ELISA), it was noted that the majority of strains isolated in the 2017-2018 epidemic season was antigenically related and interacted with antiserum against the reference strain A/Singapore/INFIMH-16-0019/2016 (MDCK-Siat1) at a homologous titer. According to the sequencing data, it was established that during the 2017-2018 epidemic season, viruses of subclade 3C.2a2, as well as 3C.2a3 and 3C.2a1b were detected in Russia. Thus, an increasing genetic heterogeneity of A(H3N2) viruses was revealed in Russia.