Neuraminidase Inhibitor Susceptibility of Influenza Viruses Circulating in Bulgaria during the Last Four Consecutive Epidemic Seasons (2011/12 to 2014/15)

Abstract

Emergence of resistant influenza virus progeny to currently approved antiviral drugs determines the need for antiviral susceptibility monitoring. The aim of the present study is to analyze neuraminidase inhibitor susceptibility of influenza viruses circulating in Bulgaria during the 2011/2012, 2012/2013, 2013/2014 and 2014/2015 flu seasons. A phenotypic fluorescence-based assay with MUNANA substrate was conducted with 93 influenza A(H1N1)pdm09, A(H3N2) and type B isolates. Screening of 352 influenza A(H1N1)pdm09 viruses was carried out using a Real Time RT-PCR discrimination assay for detection of the H275Y oseltamivir resistance point mutation. Phenotypic (IC50) evidence for resistance or reduced susceptibility to neuraminidase inhibitors was not found for any of the influenza A(H1N1)pdm09, A(H3N2) and type B viruses screened. Only one (0,3%) influenza A(H1N1)pdm09 virus carrying the H275Y substitution was detected. Real Time RT-PCR assay could be applied to screen large numbers of clinical A(H1N1)pdm09 influenza virus positive samples for oseltamivir resistance. The present study highlights the importance of continued influenza antiviral susceptibility monitoring in clinical specimens