Study On Prevalence And Virus Genetic Characterization Of Influenza B During 2010 To 2015 In Fujian Province

Objective:In order to elucidate the genetic variation of influenza B virus,to provide scientific basis for the prevention and control of influenza B and the development of vaccine, this study was carried out to analyze the prevalence of influenza B and the molecular characteristics of haemagglutinin and neuraminidase of influenza B virus strains during the period from 2010 to 2015 in Fujian Province. Methods:The surveillance information about influenza from sentinel hospitals during the period from 2010 to 2015 were collected anf analyzed by using SPSS software. The bioinformatical and statistical softwares were applied to stitch and align nucleotide sequences of HA and NA of influenza B virus, and the characteristics of the changes in HA and NA protein amino acid sites of influenza B virus were further analyzed. Results: 1?The peak of the epidemic caused by influenza B?influenza A(H1N1) and seasonal influenza A(H3N2) alternated in Fujian Province after 2009 Pandemic Influenza A(H1N1). 2?The results of surveillance of influenza B revealed that the influenza B was more active in spring and winter seasons, and there are statistically significant difference of positive rate of influenza B between different age groups and regions, especially the 5~24 years were high-risk groups and the positive rate of influenza B in coastal areas were significantly higher than in other regions. 3? Amino acid homology analysises revealed that the amimo acid homologies of HA and NA genes in influenza B virus isolates were kept highly compared with vaccine strains at the same period. 4 ? Genetic evolution analysises showed that there were BY-HA/BV-NA recombinant influenza B virus in Fujian Province in the year of 2013~2014. 5?Molecular characteristics of hemagglutinin analysises pointed out that 45 amino acid substitutions were found in the HA protein among Yamagata lineage isolates, and the number of variation sites gradually increased over time, particually in the isolates in 2011?2014 and 2015. Compared with the Yamagata lineage isolates, Victoria lineage isolates had a lesser extent of variation and no obvious accumulated trend in the HA gene. 6?Molecular characteristics of neuraminidase analysises revealed that 28 amino acid substitutions were found in the NA protein of non-reassortant Yamagata lineage isolates, of which 10 sites repeatdly changed, and 31 amino acid substitutions were found in the NA protein of Victoria lineage isolates,of which 8 sites repeatdly changed and 18 sites variablly changed. The reassortant Yamagata lineage isolates were significantly different from the two kinds of lineage vaccine strains in NA gene. 7?There was a hysteresis phenomenon between Yamagata lineage isolates and vaccine strains. It was found that the Yamagata vaccine strains of 2010 and 2015 might have no protective effect for the population with vaccine immunlization,while others might play only partial effection. The Victoria vaccine strains still play good protective effect on the population. 8? It was found that the amino acids of active site of enzyme and related sites around the NA gene remained highly conserved and there was no resistance-associated mutations. 9? Glycosylation analysis showed that a new glycosylation site was found in 196 site of HA in Yamagata lineage isolates.The site was lacated in 190 helix of antigenic epitopes and also acted as a receptor binding sites which might affect the recognition and binding of antibodies with influenza virus. Some isolates acquired a glycosylation in 463 site of NA, but it should need to be further studied whether it could affect the proliferation and adaptability of viruses. Conclusions:The surveillance on influenza epidemic and the genetic characterization analysis of virus can provide an important basis for the prevention and control of influenza. In our study,we found that genetic reassortment and antigenic drift are the main evolutionary ways of influenza B virus in Fujian province. The influenza B virus had gradual variations as time went on, and the virus isolates in some years didn't match well with the vaccine strains. Antigenic drift was found in 41 isolates among all the 99 isolates. It is forecasted that influenza B epdiemic may be continuely caused by two virus lineages alternately in Fujian Province in future.