AN ETIOLOGICAL MONITORING ON INFLUENZA AND THE GENETIC EVOLUTION OF NEURAMINIDASE GENE FOR SEASONAL H1N1 INFLUENZA A VIRUSES IN CHENZHOU IN 2009

[Objective]To analyze the epidemic situation and distribution of types of influenza virus in Chenzhou in 2009,and study the genetic evolution of neuraminidase(NA)gene of influenza A/H1N1 virus.[Methods]Throat swab samples were collected from patients with Influenza-like illness(ILI)in the sentinel hospitals,then inoculated in Madin-Darby canine kidney(MDCK)cell lines.The types of influenza were identified by hemagglutination(HA)and hemagglutination inhibition(HI)tests.A/H1N1 influenza viruses were detected by reverse transcriptase-polymerase chain reaction(RT-PCR)in the influenza outbreaks.The NA genes of two strains of influenza viruses(A/HunanBerhu/1237/2009_Apr and A/HunanBerhu/11291/2009_Oct)were sequenced to analyze their characteristic.[Results]A total of 2 226 throat swab specimens were collected,of which 109 strains were seasonal H1N1 influenza A viruses,97 influenza A-H3N2 viruses,30 novel influenza A/H1N1 virus,18 influenza B viruses.3 040 samples were detected by PCR,of which 1 016 strains were positive for influenza virus(33.43%).Compare with the WHO recommended vaccine strain of 2009(A/Brisbane/59/2007),the nucleotide sequence homology of the NA gene of A/HunanBerhu/1237/2009_Apr and A/HunanBerhu/11291/2009_Oct are 99% and 98%.The genetic evolution analysis revealed that the NA gene of A/HunanBerhu/1237/2009_Apr had the closest genetic relationship with the vaccine strain,and some sites of the NA gene of A/HunanBerhu/11291/2009_Oct were mutated.[Conclusion]Seasonal H1N1 influenza A viruses was the dominant strain during January to June.July to September was seasonal H3N2.October to November was Novel influenza A/H1N1 virus,which caused the emergence of pandemic influenza H1N1.The variation of NA gene of seasonal A/H1N1 has occurred in a certain degree.So it is very necessary to continuously monitor the variant of influenza A virus.