Reassortment And Evolution Analysis Of The Full Genome Of Influenza B Virus

Background:The current circulating influenza B virus was divided into two lineages, which was B-Victoria lineage (BV) represented by B/Victoria/2/87(Vic87) and B-Yamagata lineage (BY) represented by B/Yamagata/16/88(Yam88). The mainly natural host of influenza B virus is human. Usually, influenza B virus only causes local epidemic, and has never caused any pandemic. However, influenza B virus could circulate at different levels every year, and become predominate strains in some flu seasons. As one component of influenza vaccine, in the past years, the studies on influenza B virus were mostly focused on the mutation of HA and NA segments which encoding the surface antigens. Studies related to the reassortment of the full genome of influenza B virus were limited, although such kind of study was very important for understanding the evolution of influenza B virus.Objectives:To study the reassortment and evolution of the full genome of influenza B virus which were isolated from year1959to2013.Methods:We analized the sequences which were downloaded from GenBank and sequenced the full genome of B viruses in CNIC. We used Simplot program to detect reassortment variations, what’s more, MEGA program was used to verify the results.Results:In the69representative strains in China, we identified12reassortant viruses, including7intra-lineage and5inter-lineage reassortant viruses.The earliest reassortment detected was in1987, the B/Jingfang/9/1987virus. We also confirmed that BV and BY lineage successively appeared, at least after1959. And BV lineage was detected as early as1975. In the66global representative strains, we found22reassortments, among them9was intra-lineage and13was inter-lineage reassortments. Both Simplot program and MEGA had got the similiar resuls.Conclusions:Simplot could be used to rapidly detect reassortments of influenza B virus; reassortments occurred frequently in influenza B virus including inter-lineage and intra-lineages reassortments. Reassortments of segments encoding both internal proteins and surface proteins could be detected.