Evidence of Synergistic Activity of Medicinal Plant Extracts against Neuraminidase Inhibitor Resistant Strains of Influenza Viruses

The frequent emergence of drug resistant influenza viral strains emphasizes the urgent and con-tinual need to develop new antiviral drugs. Given the encouraging findings of previous studies on antiviral compounds from plant sources, this study focused on medicinal plants from Borneo that were traditionally used to treat symptoms of influenza infection. Following the promising results of earlier investigations, four plant extracts that demonstrated multiple modes of viral inhibition were studied against wild-type and neuraminidase (NA) inhibitor-resistant strains of Types A and B influenza viruses. The extracts exhibited more pronounced activities against the wild-type vi-ruses than the NA inhibitor-resistant strains. Variations in the antiviral potential of the extracts collected from different parts of the same plant were also evidenced in the in vitro micro-inhibi-tion assays. Even though all plant extracts affected NA activity of all viruses, only two extracts demonstrated hemagglutination inhibitory (HI) activities against Type A pandemic H1N1 and Typ