Primary Study On The Molecular Epidemiology Of Influenza Viruses In Tianjin

Influenza is a common acute infectious disease which is harmful to human health. Influenza virus is very famous for its wide range and frequent variation, so the virus surveillance is quite important. Influenza is the first infectious disease which was practiced surveillance around the world. Tianjin was admitted to one of the Influenza Surveillance Networks by WHO from 2001.The purpose of this study is to investigate Influenza epidemiology in,Tianjin and provide molecular biology basis for Influenza prevention and cure. 543 samples were collected from influenza-like patients in Tianjin from 2001 to 2003, MDCK cell and 9-11 day-old embryonated eggs were used to virus cultivation and isolation. We got 13 viruses of A1(H1N1), 75 viruses of A3(H3N2) and 99 viruses of B. The circulating dominant strain was belong to A3(H3N2)(42/64) in 2001-2002, while the B(90/123) strain was dominant in 2002-2003 The circulating dominant strain changed from A3(H3N2) to B during this period.Second, we noticed an interesting phenomenon that some strains A (H3N2) that isolated were unable, in several passages in MDCK cell culture, to agglutinate chicken erythrocytes, which called "O" phase viruses. In order to further examine the underlying mechanism, we extracted RNA, performed RT-PCR to amplify the HA1 region of the HA gene, presumed to be involved in the switch of haemagglutination properties, from the corresponding viruses. We have also cloned the PCR amplified products into PMD-18 or pGEM-T easy vectors which will be subjected to DNA sequencing. The sequence comparing shows, the "O" phase viruses are distinguished by one signature amino acid- Hisl83, when compared to "Df phase isolates we got. There was no other amino acid changed. But others report that the amino acid on 183 of "D" viruses was His amino acid too. This result demonstrates the mechanism of "O" phase variation is complicated, that mechanism maybe related to secondary structure of HA protein or the virus receptor on the cell surface. Further research need to be done to make it clear.In the subsequent research, we did analysis on the antigen variation of B isolates. We choose 8 viruses as our study object out of 90 positive isolates, we extracted RNA, performed RT-PCR-SSCP to screen the mutation on the amplified region of 308 bp, which includes the easy-mutable sites recently. 4 viruses were chosen to do sequence. Our result shows, the homology of the 308bp amplified region between B/Hongkong/330/2001 (Victoria) and B/tianjin/02/145-like , B/tianjin/02/221-like, B/tianjin/02/222-like were 96/4%, 96.4%, 99.0% at nucleotide level, respectively; while the homology between B/Sichuan/379/99(Yagamata) and B/tianjin / 02 / 121-like was 93.1% at nucleotide level. The result reveals that the antigen variation of B influenza in tianjin is not great. Our research also indicates" the feasibility of PCR-SSCP method for screening of circulating influenza viruses in future work. This new method used on influenza deserve our further research.