| Objective: To study the influenza activity and the characteristics of HA1 gene of influenza virus isolated in Hebei Province during 2007~2008 influenza season. To elucidate the relationship between the influenza epidemic/outbreak and the variation of HA1 region of the virus. In order to provide the scientific basis for the prevention and treatment of influenza.Methods:1 The data of ILI (Influenza-like illness) were collected from 12 sentinel hospitals in 5 cities by Influenza surveillance information system from October 2007 to March 2008, and analyzised by Excel software.2 The pharynx swabs specimens were collected from the ILI by trained staff. The specimens were inoculated into MDCK cell flasks for influenza virus. The isolates were identified for influenza virus type and subtype by hemagglutination inhibition (HI) assay with the red cell of guinea pig's and reference antiserum. We selected 14 strains which were choosen by different time, geography and type of influenza virus on the base of HI test.3 RNAs were extracted and their HA1 gene segments were amplified by reverse transcription polymerase chain reaction (RT-PCR). The purified PCR products were sequenced. Using the DNAStar software, the sequences of nucleotide and amino acid of HA1 were compared with that of the vaccine strains recommended by WHO.Results:1 The ILI percentage of the sentinel hospitals was 0.588%, peaked at the fifth week of 2008(5.07%), and higher among paediatric department.2 Total 79 influenza strains were isolated from 962 clinical specimens of sentinel hospitals, in which, 68 were Yamagata- lineage viruses, 7 Victoria-lineage viruses and 4 H3N2 viruses.3 Two influenza B Yamagata-lineage viruses and four H3N2 viruses were isolated from two influenza outbreaks, respectively.4 The HA1 gene fragments of the 14 strains were amplified by RT-PCR using specific primers. After 1.5% agarose gel electrophoresis, the expected bands appeared.5 Amplification of the influenza virus HA1 gene fragments were sequenced and compared with the vaccine strain recommend by WHO. The nucleotide sequences, amino acid sequences and homology comparison were analysised.5.1 There were six amino acids sites replaced (3F>L, 45S> N, 158R>K, 171N>K, 173N>K, 304A>V),comparing the 2008 H3N2 strains with A/Hebeixinshi/1255/2007 which was isolated in 2007.One of the six sites located in antigenic determinant cluster B(158R>K), two at antigenic determinant cluster C (45S>N, 304A>V) and two at antigenic determinant cluster D(171N>K, 173N>K). Compared the 2008 strains with A/Wisconsin/67/2005 which was the vaccine strain recommend by WHO in 2007-2008 influenza season, we found that the similarities of nucleotide and amino acid sequence were 98.0% and 97.0% ,respectively, and ten amino acids were substituted. The phylogenic tree showed that they were A/Brisbane /10/2007-like virus. (A/Brisbane/10/2007 virus was the vaccine strain recommend by WHO in 2008-2009 influenza season.)5.2 Compared with the vaccine strain B/Malaysia/2506/ 2004,the four Victoria-lineage strains of influenza B virus had no loss or insert of nucleotides and the nucleotide homology was 98.8 % ~ 99.1% ,while the amino acid homology was 99.1% ~ 99.4%.All the isolates contained the same amino acid substitution at position 109(N>K).5.3 Yamagata-lineage strains and the vaccine strain B/Malaysia/2506/2004 did not belong to the same lineage. As compared with the B/Shanghai/361/2002 which was the vaccine strain recommend by WHO in 2005-2006 influenza season, the nucleotide homology was 97.5% ~ 97.8% and the amino acid homology was 97.4% ~ 98.0%. Seven amino acid were substituted (37T>V, 40Y>H, 48K>R, 108A> P, 131P>L, 196N> D ,251M>V), and 131,196 positions of amino acid located in antigenic determinant sites. Conclusion:1 The time of ILI visiting and the strains isolated appeared about the same period, the peak was from December 2007 to January 2008.The Yamagata-lineage virus was the dominant strain.2 The H3N2 strains underwent greater genetic variation, and ten positions of amino acid were different compared with the vaccine strain A/Wisconsin/67/2005. They were newly emerging strains which were the 2008-2009 influenza season vaccine strain A/Brisbane /10/2007-like virus.3 The gene of Yamagata-lineage strain was mutated, so the antigenicity was shifted.The Yamagata-lineage strains did not belong to the same lineage when compared with the vaccine strain B/Malaysia/2506/2004.All of these made up the main reasons of local outbreak of influenza.4 There was no apparent variation of Victoria-lineage viruses. The strains were the vaccine strain B/Malaysia/ 2506 /2004-like viruses, but continue circulating in the population.5 Monitoring the genetic changes in HA1 domain of the epidemic strains can help us to find newly emerging strains with epidemiologic significance early.
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