Monitoring of influenza A H5N1 virus from avian species in border areas between Thailand and neighboring countries (Laos and Myanmar)

To monitor Influenza A H5N1 virus from avian species in border areas between Thailand and neighboring countries (Laos and Myanmar) from September 2007 to June 2008. Two-thousand one hundred seventy five samples, including 2,139 live birds and 36 visceral organs, were collected. The H5N1 viruses were isolated and identified using embryonated egg inoculation, Hemagglutination test, Multiplex RT-PCR, Realtime RT-PCR, and PCR-ELISA. Then, the viruses were genetically characterized by using sequencing of whole genome avian influenza H5N1 viruses, phylogenetic analysis, and analysis of key determinant residue changes of 8 genes (PB2, PB1, PA, HA, NP, NA, M, and NS). The results revealed that the evidence of avian influenza H5N1 virus was 0.69% (15/2,175). The viruses had common genetic characteristics of Highly Pathogenic Avian Influenza (HPAI), with multiple basic amino acids in the HA cleavage site and a 20-amino acid deletion in NA stalk region. No point mutations were identified in the key determinant residues of those genes. Phylogenetic analysis of whole genes showed that the viruses clustered within the lineage of H5N1 avian isolates from Thailand-Vietnam lineage, genotype Z or clade 1. These indicate that avian influenza H5N1 virus circulating in border areas between Thailand, Laos and Myanmar were genetically related to avian influenza H5N1 virus in 2004-2006 in Thailand. In summary, this study presented the evidence of HPAI spreading in border area between Thailand and neighboring countries (Laos and Myanmar). Therefore, monitoring and surveillance of avian influenza virus along the border areas will be beneficial for prevention and control of H5N1 infection in humans.