Owing to its deep active site cleft, the NA has been an attractive target for drug design. Both zanamivir and oseltamivir were designed by modifying the sialic acid (SA) structure. The two FDA-approved clinical drugs were once successfully used to inhibit the spread of influenza viral progeny [15] by binding to viral surface glycoprotein of neuraminidase (NA) [15] . However, it has also been found from several clinical cases [16, 17, 18] that oseltamivir failed to treat avian influenza virus. It is both antigenic drift (sequence base mutations) and antigenic shift (genetic recombination) of segmented RNA genome of influenza viruses that have caused the NA inhibitor being resistant [19, 20] .