Antigenic and genetic analyses of influenza B viruses isolated in Lusaka, Zambia in 1999.

Previous studies of the hemagglutinin (HA) genes of various influenza B virus isolates demonstrated the existence of two antigenically distinct virus lineages represented by B/Victoria/2/87 and B/Yamagata/16/88, respectively. Here, we investigated the antigenic and genetic characteristics of influenza B viruses isolated from children living in Lusaka, Zambia between January and May 1999. Antigenic analysis with chicken antiviral sera showed that all the Zambian isolates had the HA protein belonging to B/Yamagata/16/88-related lineage. Furthermore, phylogenetic analyses of the eight RNA segments performed by using the total or partial nucleotide sequences of the two representative Zambian strains (B/Lusaka/270/99 and B/Lusaka/432/99) as well as the previously reported sequences suggested that the Zambian viruses are closely related to the recently circulating reassortants represented by B/Shiga/T30/98 and B/Yamanashi/166/98 which acquired the genes coding for three polymerase proteins (PB2, PB1, and PA), HA, nucleoprotein, and matrix protein from a B/Yamagata/16/88-like parent and the gene encoding nonstructural proteins (NS1 and NS2) from a B/Guandong/8/93-like parent.