Sialic acid (SA) as a natural ligand combines with both of the glycoproteins (HA and NA) and located at the membrane of host cell, which is the basis of heme-agglutination when viruses are mixed with blood cells and entry of the virus into cells of the upper respiratory tract [11, 12] . According to the mutagenic analysis the residues of both HA1 and NA binding sites are quite conserved for most influenza A strains [13, 14] .