Antiviral activity and molecular targets of plant natural products against avian influenza virus

Background: Avian influenza, commonly known as bird flu, is caused by viruses adapted to birds; however, some of the avian viruses are highly pathogenic to the human population. Though vaccines have been developed for the prevention of avian influenza, the emerging resistant strains greatly limit the effectiveness of these mainstay prophylactic drugs. Thus, novel anti-avian influenza agents are sought for the dissemination of such resistance crisis. Plants in great biological diversities stand as infinite resources for the development of novel anti-influenza agents. Objective & Method: In this article, a comprehensive review of the discovered anti-avian influenza agents from plant origins up to December of 2015 is provided. After introducing the epidemics of avian influenza and the current preventive measures and treatments, a brief summary of the influenza A virus replication cycle is illustrated, in which the major processes of viral infection are discussed. The ethnopharmacology of anti-avian influenza plant-based natural products is reported. These botanical anti-avian influenza agents are further presented according to their modes of action and molecular targets. The actions of plant-based natural products typically range from interfering with the viral entry, replication, transcription and translation, nuclear export of viral materials, viral assembly, packing, budding to enhancing the host response against the viral infections. Moreover, the chemical structures and challenges in the discovery of some typical anti-viral compounds are explained in detail. According to this review, hundreds of botanical anti-avian influenza agents have been discovered. Conclusion: Collectively, the discovery of anti-avian influenza agents derived from plants largely involves multidisciplinary approaches of botanical, phytochemical and biological techniques, which are also heavily applied to the development of synthetic compounds for other therapeutic uses.