| Objective: To study the influenza activity and the characteristics of HA1 gene of influenza virus isolated in Hebei Province during 2005~2006 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 of the prevention and treatment of influenza.Methods: The data of ILI (Influenza-like illness) were collected from 12 sentinel hospitals in 5 city by Influenza surveillance information system during October 2005 to March 2006, and analyzised with Excel software. The specimens which were pharynx swabs were collected from the ILI who visited the four sentinel hospitals 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 HI assay whit the red cell of guinea pig's and reference antiserum. According to the sampling time and type, we randomly sampled 9 isolates,H1N1, H3N2 and B, three in each subtype, together with the four isolates isolated from influenza outbreaks,amplified their HA1 gene. RNAs were extracted by Trizol reagent 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 nucleotide and amino acid sequences on HA1 protein molecular of influenza virus were compared with that of influenza viruses which were epidemical in recent years or vaccine complement recommended by WHO.Results: The ILI visiting ratio to Medical Department of the sentinel hospitals was 0.588%, it peacked twice, once at 0.848% in December,2005, and again at 0.756% in January,2006. The ILI visiting ratio to paediatric clinic was 9.821%, which peacked thrice, once at 10.539% in November,2005, and again at 11.249% in December, 2005, another at 10.709% in January, 2006. Most of the ILI are children under 5-years-old, the constituent ratio was 55%(10914/19829), which accorded with the data obtained in former seasons.92 influenza strains were isolated from 938 clinical specimens from ILIs by MDCK (Madin-Darby canine kidney) cells, and 92 were positive (9.81%), Of these, 57 (61%) influenza A (H1N1) viruses, and 6 (7%) influenza A (H3N2) viruses, and 33 (32%) B viruses. Four influenza B viruses were isolated from the 15 specimens from two influenza outbreaks. Influenza A (H1N1) predominated from October to December, 2005. Influenza B predominated from February to March, 2006, and which caused the influenza outbreaks.The influenza H1N1 viruses from Hebei province in 2005~2006 are different from the A/New Caledonia/20/1999, which was the vaccine strain recommend by WHO at that time, in nucleotide sequence of HA1 gene. As compared with to the A/New Caledonia/20/1999 virus, there was an identity of 97.0%~98.1% in nucleotide sequence, and obviously different from A/New Caledonia/20/1999 in phylogenic tree, but amino acids was not found locating in antigenic determinant sites. The HA1 of the influenza H3N2 viruses isolated in Hebei province during 2005~2006 were simalar to the A/Calfornia/7/2004, which was the vaccine strain recommended by WHO in that season. Compared with the A/Calfornia/7/2004 virus, there are an identity of 98.7%~99.0% in nucleotide sequence, and similar to A/ Calfornia/7/2004 in phanylogenic tree. Three amino acids were substituted in HA1, two located in B antigenic determinant site (188N>D, 193S>F) and another one at receptor binding site (225D>N). The influenza B viruses of Hebei province in 2006 were Victoria-like-strain, and which was different from the B/Shang hai/361/2002, the latter was Yamagata-like-strain. Comparing to the B/Hong Kong/330/2001 virus, which was the recently epidemic representative strain of Yamagata-like-strain, which had an identity of 96.4%~96.8% in nucleotide sequence, and far away from B/Hong Kong/330/2001 in phylogenic tree, six variant amino acids were found locating in antigenic determinant sites (80K>R, 116R>H, 121N>T, 129K>N, 164E>D, 197S>N).Conclusion: During the 2005-06 influenza season, influenza A (H1N1), A (H3N2), and B viruses cocirculated in Hebei province. Influenza A (H1N1) and influenza B viruses predominated. Influenza A (H3N2) viruses circulated at lower levels.Influenza H1N1 viruses occurred evident genovariation in HA1 region, but they did not locate in antigen determinant sites. It was its low popularity in continuous years that made the population's immunologic barrier break down, which caused the influenza H1N1 activity and outbreak.Though influenza H3N2 viruses circulated at lower levels, which occurred genovariation in antigen determinant sites of HA1 region, its vaccine strain would be renewed.Influenza B viruses currently circulating could be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses. The new isolations of Influenza B viruses represented a change from B/Yamagata lineage to B/Victoria lineage. Compared with the B/Hong Kong/330/2001 that occured evident genovariation in HA1 region and six replacements of amino acids locating in antigen determinant sites, which caused the antigenic shift. The epidemic and outbreak of influenza B virus could be contributed to it. They are new variants and would be paid close attention. The vaccine strain will be changed.
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