Epidemiology of human influenza A and B viruses in myanmar from 2005 to 2007

Objectives: To perform genetic analysis of influenza A and B viruses in Myanmar from 2005 to 2007 and to determine the prevalence of amantadine-resistant influenza A viruses. Methods: Phylogenies of the HA and NA genes were analyzed and mutations in M2 that confer resistance to amantadine were screened. Results: Influenza in Myanmar exhibited seasonality, which coincided during the rainy season from June to August. Out of 2,618 samples, 76 influenza A and 132 influenza B viruses were isolated. Phylogenetic analysis showed that in 2005, 11 A/H1N1 isolates formed one cluster with A/Solomon Islands/3/2006 and were amantadine-sensitive strains. One A/H3N2 isolate was amantadine-resistant harboring S31N mutation in M2 and possessing S193F and D225N substitutions in HA (clade N), similar to A/Wisconsin/67/2005. No viruses were isolated in 2006 due to sample storage failure. In 2007, all 64 A/H3N2 isolates were amantadine-resistant and similar to A/Brisbane/10/2007. For influenza B, 3 Yamagata-lineage and 17 Victoria-lineage isolates were detected in 2005 and 112 Victoria-lineage viruses were isolated in 2007. All Victoria-lineage isolates were reassortants possessing NA derived from the Yamagata lineage. Conclusion: Continuous surveillance in tropical countries is important for elucidating the seasonality of influenza and determining the molecular characteristics of circulating strains.