Genetic characterization of nonstructural genes of H5N1 avian influenza viruses isolated in Thailand in 2004-2005.

The outbreak of highly pathogenic avian influenza (HPAI) viruses has severely dis- rupted poultry production and trade. Humans have been infected with HPAI H5N1 viruses and many have died. The nonstructural (NS) proteins of the virus are a factor that determines virulence. In this report, 80 NS genes of H5N1 HPAI viruses isolated from Thailand were com- pletely sequenced and phylogenically analyzed. The percentages of identity and variable site NS1 genes were similar to NS2/nuclear export protein (NEP) genes. All NS1 genes from the samples were located in allelic group A. The NS1 and NS2/NEP proteins possess 225 and 121 amino acids, respectively. All NS1 protein samples had five amino acid deletions typical of avian influenza viruses isolated since 2002. An amino acid substitution at position 92 (G92E) of the NS1 protein, known to promote the inhibition of host immune responses, was also found in the samples.