Surveillance of influenza B viruses and sequence analysis of HA₁ in Ningbo city, 2003 - 2009

Objective To understand the prevalence and genetic characteristics of two lineages of influenza B viruses isolated recently in Ningbo. Methods Influenza viruses were isolated with madin-darby Canine Kidney (MDCK) cell, and the representative strains were selected according to the lineages of influenza B viruses isolated during 2003 - 2009, the target genes were amplified by reverse transcriptase polymerase chain reaction (RT-PCR), the product was purified and determined for nucleotide sequence of HA1 region of the haemagglutinin gene of influenza B viruses. Results During 2003 - 2009, two lineages of influenza B viruses co-circulated in Ningbo nearly every year which were predominant alternatively. Yamagata lineage virus predominated in 2004 and 2007 relatively, but Victoria lineage virus was highly prevalent in March, 2006 and in June, 2009. The HA1 region sequencing indicated the obvious amino acid substitution for Yamagata lineage virus in 2004 and 2007 and for Victoria lineage virus in 2005 and 2009. Conclusion During 2003 - 2009, the haemagglutinin genes of two lineages of influenza B viruses had obvious difference. The predominance of Yamagata lineage virus in 2004 and in 2007 and the high prevalence of Victoria lineage virus in 2006 and 2009 in Ningbo were related to the amino acid substitution of HA1 region of influenza B viruses.