Isolation and evaluation of antiviral plant compounds against respiratory disease-causing viruses: a review

Influenza viruses are major concern worldwide due to their fast ability to spread, and causing the respiratory illness of varying severity. The rate of travel, urbanization and socializing among the people are the major factors for the spread. The coronaviruses causing the contagious respiratory illness are similar to influenza viruses. The ongoing COVID-19 pandemic serves as an example on how a single influenza virus can greatly disrupt the economy and social activity worldwide on unprecedented scale. The emergence of the new variants also presents threat for the development of drugs and/or vaccines for the treatment of viral infection. Hence, researchers worldwide have been focusing into plant compounds to identify effective bioactive compound which could be developed into therapeutic antiviral drugs against influenza viruses and coronaviruses. The aim of this paper is to summarize the bioactive compounds isolated from plants that exhibit potential against influenza viruses and coronaviruses. This paper also investigates the techniques used in isolation, characterisation and elucidation of antiviral activity of plant compounds in the evaluation and application of such compounds for therapeutic purpose.