Traceability of the A/H3N2 virus borne influenza pandemic in Zhejiang province,1998 / 中华流行病学杂志

ABSTRACT

Objective To trace back to the influenza pandemic caused by A/H3N2 virus happened in Zhejiang province,1998.Methods The whole genome of three isolates related to Zhejiang influenza virus was amplified through RT-PCR,and the identified sequences were aligned with the sequences downloaded from GenBank of the H3N2 strains which were circulating in other regions during 1995 to 1998.The crossing HAI titers of the reference strains were measured by HAI test and antigenic ratios were calculated.Results The Phylogenetic tree,constructed based on HA sequence showed that the dominant strains A/Zhejiang/11/98 and A/Zhejiang/18/98 were significant different from the isolates circulated in other regions during 1995 to 1996 and the strains isolated in the mainland of China,in 1997.Although the A/Zhejiang/11/98 and A/Zhejiang/18/98 strains were distributed in the same cluster with A/Sydney/5/97,the two strains were closer to the epidemic strains isolated in Hong Kong and New York in the later part of 1997.Based on HAI,NA and MP genes,A/Zhejiang/18/98 seemed to be the closest one to the Hong Kong epidemic strains,and the genetic distances between A/Zhejiang/18/98 and New York strains were shorter than that with A/Sydney/5/97 based on PA,HA and NS genes.There were only 1-3 amino acid differences between A/Zhejiang/18/98 and Hong Kong or New York strains,whereas 7 amino acid differences with A/Sydney/5/97,in which three were located in the antigenic determinant regions.Data from the crossing HAI test showed that the antigenic ratio between A/Zhejiang/18/98 and A/Sydney/5/97 had reached 2.0,indicating the antigenic difference to a certain extent.Additionally,the onset of the influenza epidemic during 1997 to 1998 also suggested the possible route of transmission related to this H3N2 virus.Conclusion The influenza pandemic occurred in Zhejiang province in 1998 was possibly caused by the importation of a newly identified H3N2 influenza variant via Hong Kong and New York in late 1997.