Abstract
Influenza B virus, which causes acute respiratory infections, has increased in prevalence in recent years. Based on the nucleotide sequence of the hemagglutinin (HA) gene, influenza B virus can be divided into two lineages, Victoria and Yamagata, that co-circulate during the influenza season. However, analysis of the potential association between the clinical and virological characteristic and the lineage of influenza B viruses isolated in Thailand was lacking. To investigate influenza B virus genetically and determine its neuraminidase (NA) inhibitor susceptibility phenotype, a total of 6920 nasopharyngeal-wash samples were collected from patients with influenza-like illness between the years 2011 and 2014 and were screened for influenza B virus by real-time PCR. Of these samples, 3.1% (216/6920) were confirmed to contain influenza B viruses, and 110 of these influenza viruses were randomly selected for nucleotide sequence analysis of the HA and NA genes. Phylogenetic analysis of the HA sequences showed clustering into various clades: Yamagata clade 3 (11/110, 10%), Yamagata clade 2 (71/110, 64.5%), and Victoria clade 1 (28/110, 25.5%). The analysis of clinical characteristic demonstrated that the Victoria lineage was significantly associated with the duration of hospitalization, number of deceased cases, pneumonia, secondary bacterial infection and underlying disease. When combined with phylogenetic analysis of the NA sequences, four samples showed viruses with reassortant sequences between the Victoria and Yamagata lineages. Statistical analysis of the clinical outcomes and demographic data for the reassortant strains did not differ from those of the other strains in circulation. Oseltamivir-resistant influenza B viruses were not detected. Our findings indicated the co-circulation of the Victoria and Yamagata lineages over the past four cold seasons in Bangkok. We also demonstrated differences in the clinical symptoms between these lineages.
Highlights
Influenza viruses comprise three members: influenza A, influenza B, and influenza C
Influenza B virus cannot be classified into distinct subtypes; based on genetic analysis it can be divided into two lineages, denoted B/Victoria/2/87 and B/Yamagata/16/88 [1, 2]
Global circulation of influenza viruses including influenza A virus and influenza B virus was detected every year depending on the climate
Summary
Influenza viruses comprise three members: influenza A, influenza B, and influenza C. Influenza A and B viruses are associated with annual worldwide epidemics. Influenza B virus cannot be classified into distinct subtypes; based on genetic analysis it can be divided into two lineages, denoted B/Victoria/2/87 and B/Yamagata/16/88 [1, 2]. Both lineages were first detected in 1988–1989 and co-circulated globally in the 1990s, with the Yamagata lineage being predominant [3,4,5]. During 2000–2002, the Victoria lineage became predominant worldwide [6]. The level of cross protection offered by antibodies between two strains of influenza B virus was investigated but not detected [9]
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