Differing epidemiological dynamics of influenza B virus lineages in Guangzhou, southern China, 2009-2010

Abstract

The epidemiological and evolutionary dynamics of the two cocirculating lineages of influenza B virus, Victoria and Yamagata, are poorly understood, especially in tropical or subtropical areas of Southeast Asia. We performed a phylogenetic analysis of the hemagglutinin (HA) and neuraminidase (NA) sequences of influenza B viruses isolated in Guangzhou, a southern Chinese city, during 2009 to 2010 and compared the demographic and clinical features of infected patients. We identified multiple viral introductions of Victoria strains from both Chinese and international sources, which formed two phylogenetically and antigenically distinct clades (Victoria 1 and 2), some of which persisted between seasons. We identified one dominant Yamagata introduction from outside China during 2009. Our phylogenetic analysis reveals the occurrence of reassortment events among the Victoria and Yamagata lineages and also within the Victoria lineage. We found no significant difference in clinical severity by influenza B lineage, with the exceptions that (i) the Yamagata lineage infected older people than either Victoria lineage and (ii) fewer upper respiratory tract infections were caused by the Victoria 2 than the Victoria 1 clade. Overall, our study reveals the complex epidemiological dynamics of different influenza B lineages within a single geographic locality and has implications for vaccination policy in southern China.

Fig 1

Map of Guangzhou City, China, and study sites. The Baiyun, Yuexiu, Liwan, and Haizhu districts in central Guangzhou City are in red. Other districts are in blue or green. Six study sites are shown as circles with different colors and described in the key.

Fig 2

Influenza virus activity in Guangzhou City from April 2009 to September 2010. (A) Monthly number of laboratory confirmed influenza infection by type: influenza B virus in red, pandemic H1N1/2009 in green, and seasonal influenza A virus in blue. (B) Monthly number of influenza B virus infections by the Victoria (B/Victoria/2/87) and Yamagata (B/Yamagata/16/88) lineages. The 2009 and 2010 periods of influenza B virus epidemic activity are shaded in light blue and pink.

Fig 3

Global phylogenetic trees of the HA gene and NA gene of influenza B virus. (A) HA phylogeny, midpoint rooted; (B) NA phylogeny, rooted by the oldest sequence. The bootstrap support values for key branches in the trees are indicated. Sequences from different localities have their branches indicated by colors described in the key.

Fig 4

Phylogenetic trees of the HA and NA genes of the Victoria lineage of influenza B virus. (A) HA phylogeny; (B) NA phylogeny. The trees are rooted by the oldest vaccine strain, B/Hong Kong/05/1972, and bootstrap support values and major amino acid substitutions are mapped to key branches. Intraclade and intralineage reassortants are indicated as described in the key. The Brisbane/60 (pink) and the Malaysia/2506-like (light blue) clades are indicated. Between the Brisbane/60 and Malaysia/2506 clades, two South American viruses—B/Bolivia/104/2010 and B/Bolivia/1526/2010—represent a new lineage, falling close to the recently emerged clade represented by B/Bolivia/104/2010 (Bolivia/104 clade).

Fig 5

Phylogenetic trees of the HA and NA genes of the Yamagata lineage of influenza B virus. (A) HA phylogeny; (B) NA phylogeny. The trees are rooted by the oldest vaccine strain, B/Singapore/222/1979, and bootstrap support values and major amino acid substitutions are mapped to the key branches. Intralineage reassortant is indicated as described in the key. The Bangladesh/3333-like (light yellow) and Brisbane/3-like (light green) clades are indicated.