Genetic analysis of the matrix and non-structural genes of equine influenza virus (H3N8) from epizootic of 2008–2009 in India

India faced an epizootic of equine influenza in 2008–2009. The isolated viruses were typed as H3N8 and grouped with the clade 2 viruses of Florida sublineage on the basis of haemagglutinin (HA) gene sequence analysis. This report describes the genetic analysis and selection pressure of matrix (M) and non-structural 1 (NS1) genes of the Indian isolates. All isolates shared 98.41% and 99.54% homology with other clade 2 viruses of Asian origin for M1 and M2 amino acid (aa) sequences, respectively. There were 3 and 4 unique aa residue changes respectively in M1 and M2 proteins in all Asian isolates. Phylogenetic analysis revealed clustering of Indian and Chinese isolates in a separate group designated here as Asian clade for M gene. Indian and Chinese isolates shared homology ranging from 98.17% to 99.08% at aa level. The M and NS1 genes were under negative selection pressure with estimated magnitude of pressure (ω) 0.054, 0.581 and 0.30 for M1, M2 and NS1, respectively.