Medicinal Plants in the Treatment of Influenza Virus A Infections: Role of Secondary Metabolites, Clinical and Preclinical Studies, and Future Perspectives

In the current period, respiratory diseases that evolved from influenza A infection have become a burning issue to the communities throughout the world due to the unavailability of potential medicines or suitable vaccines for the management of diseases caused by influenza A virus. Out of the three types of influenza viruses, i.e., influenza A, influenza B, and influenza C, influenza A causes severe respiratory distress to human beings. Influenza virus is a single-stranded, negative-sense RNA virus belonging to the Orthomyxoviridae family. Influenza A virus has a tendency to show a high rate of mutation in genetic materials and the presence of eight discrete segments which is responsible for reassorting and producing new variant subtype viruses. This virus has the capability to cause antigenic shift resulting from the transmission of viruses easily between the various species of mammals and from bird to human. There are four components present in influenza A virus: hemagglutinin, neuraminidase, M2 ion channel, and ribonucleoprotein (RNP). Anti-influenza A drugs available in the market are neuraminidase inhibitors, e.g., oseltamivir and zanamivir, and M2 ion channel inhibitors, e.g., amantadine, rimantadine, somantadine, etc.; however, viruses are becoming resistant to these drugs due to the modification of cell structure of the virus. The researchers are driven to discover a new treatment regimen derived from plant sources that will be beneficial for the treatment of infections caused by influenza A virus. Scientific evidences are available that the whole plant extract or the extract of a specific part of a plant or a combination of medicinal plants exhibited potential anti-influenza A activity. The aim of this chapter is to highlight the description of the cell structure of influenza A virus; replication of the virus; reason for resistance to pharmaceutical drugs; the role of secondary metabolites, i.e., herbal medicines, used for the treatment of infections caused by influenza A; the chemistry of secondary metabolites or phytochemicals responsible to show anti-influenza A activity with clinical and preclinical studies; and future perspectives.