The NA proteins of two isolates had three amino RG7388 deletions at positions 61, 62, 63, which lead to lack a potential glycosylation site at position 61. However, it is unknown whether the deletions in NA protein of our H9N2 isolates are correlated with pathogenicity in mink. The HB site in the NA of Asian H9N2 IAVs was under positive selection pressure for mutations, which results in compatible combinations of HA and NA (Matrosovich et al., 2001). The influence of these mutations in the HB sites found in Mk/SD/F6/13 and Mk/SD/F10/13 remains unclear. Some amino acid substitutions of PB2, M and NS1 were associated with IAV pathogenicity in mammals (Qi et al., 2009, Seo et al., 2004, Subbarao et al., 1993 and Wang et al., 2012). Amino acid 627 of PB2 protein is an important determinant of host range and virulence of IAVs for primates (Subbarao et al., 1993). Mk/SD/F6/13 and Mk/SD/F10/13 were 627 L in PB2 protein, which is associated with adaptation to mammals (Qi et al., 2009). M gene encoded two proteins, M1 and M2. Amantadine and Rimantadine target M2 protein, and the mutation (S31N/I) in M2 protein can confer resistance to these drugs (Qi et al., 2009). The 31st residue was I in the M2 protein, indicating that Mk/SD/F6/13 and Mk/SD/F10/13 were not sensitive to Amantadine and Rimantadine. The result of animal experiments showed that mink could be infected by H9N2 IAV and presented slightly clinical signs. But no mink died of the disease, which the H9N2 IAV had low pathogenicity to mink.
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