The novelty of this strain of virus means that there are so many uncertainties surrounding its behaviour, therefore it is too early to determine whether herbal plants or compounds could in fact contribute to society as prophylactic agents or as suitable substances in anti-coronavirus drugs against Covid-19. However, due to Covid-19’s high similarity with the previously reported SARS-CoV and MERS-CoV viruses, previous published research on herbal compounds, which have been proven to exert anti-coronavirus effects, may be a valuable guide to finding anti-coronavirus herbal plants, which may be active against the SARS-CoV-2 virus.

After the breakout of SARS-CoV, first reported in early 2003[iii], scientists have been vigorously trying to exploit several antiviral compounds against SARS-CoV. This had led a group of experts in China to screen more than 200 Chinese medicinal herb extracts for antiviral activities against this coronavirus strain.

Amongst these, four extracts exhibited moderate to potent inhibition effects against SARS-CoV – Lycoris radiata (Red Spider Lily), Pyrrosia lingua (a fern), Artemisia annua (Sweet wormwood) and Lindera aggregate (an aromatic evergreen shrub member of the laurel family). The antiviral effects of these were dose dependant and ranged from low concentrations of the extract to high, varying for each herbal extract. In particular Lycoris radiata exhibited the most potent anti-viral activity against the virus strain.[iv]

This result was consistent with that of two other research groups, which suggested that an active constituent contained in Licorice roots, Glycyrrhizin, has been proven to have an anti-SARS-CoV activity by inhibiting its replication.[v] [vi]  In another study, Glycyrrhizin also exhibited antiviral activity when tested for its in vitro antiviral effects on 10 different clinical isolates of SARS coronavirus. Baicalin – a constituent of the plant Scuttelaria baicalensis (Skullcap) – has also been tested in this study under the same conditions and has also shown antiviral action against the SARS coronavirus.[vii] Baicalin has also been shown to inhibit the replication of the HIV-1 virus in vitro in previous studies.[viii] [ix] However it should be noted that in vitro findings may not correlate with in vivo clinical efficacy. This is because the oral dose of these agents in humans may not achieve a blood serum concentration similar to that tested in vitro.

Lycorine has also demonstrated potent antiviral action against SARS-CoV.3 Several previous reports suggest that Lycorine seems to have broad antiviral activities and has been reported to have demonstrated an inhibitory action on the Herpes Simplex virus (type I)[x] and the Poliomyelitis virus also.[xi]

“Other herbs which have been reported to have shown antiviral activity against SARS-CoV are Lonicera japonica (Japanese Honeysuckle) and the commonly-known Eucalyptus plant, and Panax ginseng (a root) through its active component Ginsenoside-Rb1.”[xii]

Evidence from the above-mentioned studies and several other worldwide studies report that many medicinal herbal constituents have exhibited antiviral activities against coronaviruses[xiii] [xiv] and their main mechanism of action seems to be through the inhibition of viral replication.[xv] China has extensively used traditional Chinese medicinal herbs for the treatment of SARS effectively in many cases.[xvi] However there is no substantial evidence yet on the clinical effectiveness of these for Covid-19 infected patients.

Could such herb extracts be potential candidates for the development of new antiviral medicines for the prevention or treatment of SARS?

Maria-Dolores Christofi, Bsc(hons) Health Sciences: Herbal medicine, UK

DISCLAMER: This article has been written for informational purposes only and it is not intended to substitute professional medical advice, diagnosis or treatment. If you think you may have symptoms related to those of Covid-19 or any other disease, call your doctor immediately.

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[i] Zhou, P., Yang, X., Wang, X. et al., 2020. A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature 579, 270–273 (2020). https://doi.org/10.1038/s41586-020-2012-7

[ii] Andersen, K.G., Rambaut, A., Lipkin, W.I., Holmes, E.C. and Garry, R.F., 2020. The proximal origin of SARS-CoV-2. Nature Medicine, pp.1-3.

[iii] CDC SARS Response timeline. Available at https://www.cdc.gov/about/history/sars/timeline.htm. Accessed

on 18/03/2020.

[iv] Li, S.Y., Chen, C., Zhang, H.Q., Guo, H.Y., Wang, H., Wang, L., Zhang, X., Hua, S.N., Yu, J., Xiao, P.G. and Li, R.S., 2005. Identification of natural compounds with antiviral activities against SARS-associated coronavirus. Antiviral research, 67(1), pp.18-23.

[v] Cinatl, J., Morgenstem, B. and Bauer, G., 2003. Glycyrrhizin, an active component of licorice roots and replication of SARS-associated coronovirus. Lancet, 361(9374), pp.2045-2046.

[vi] Hoever, G., Baltina, L., Michaelis, M., Kondratenko, R., Baltina, L., Tolstikov, G.A., Doerr, H.W. and Cinatl, J., 2005. Antiviral Activity of Glycyrrhizic Acid Derivatives against SARS− Coronavirus. Journal of medicinal chemistry, 48(4), pp.1256-1259.

[vii] Chen, F., Chan, K.H., Jiang, Y., Kao, R.Y.T., Lu, H.T., Fan, K.W., Cheng, V.C.C., Tsui, W.H.W., Hung, I.F.N., Lee, T.S.W. and Guan, Y., 2004. In vitro susceptibility of 10 clinical isolates of SARS coronavirus to selected antiviral compounds. Journal of Clinical Virology, 31(1), pp.69-75.

[viii] Kitamura, K., Honda, M., Yoshizaki, H., Yamamoto, S., Nakane, H., Fukushima, M., Ono, K. and Tokunaga, T., 1998. Baicalin, an inhibitor of HIV-1 production in vitro. Antiviral research, 37(2), pp.131-140.

[ix] Li, B.Q., Fu, T., Dongyan, Y., Mikovits, J.A., Ruscetti, F.W. and Wang, J.M., 2000. Flavonoid baicalin inhibits HIV-1 infection at the level of viral entry. Biochemical and biophysical research communications, 276(2), pp.534-538.

[x] Renard-Nozaki, J., Kim, T., Imakura, Y., Kihara, M. and Kobayashi, S., 1989. Effect of alkaloids isolated from Amaryllidaceae on herpes simplex virus. Research in virology, 140, pp.115-128.

[xi] Ieven, M., Vlietinick, A.J., Berghe, D.V., Totte, J., Dommisse, R., Esmans, E. and Alderweireldt, F., 1982. Plant antiviral agents. III. Isolation of alkaloids from Clivia miniata Regel (Amaryl-lidaceae). Journal of Natural Products, 45(5), pp.564-573.

[xii] Wu, C.Y., Jan, J.T., Ma, S.H., Kuo, C.J., Juan, H.F., Cheng, Y.S.E., Hsu, H.H., Huang, H.C., Wu, D., Brik, A. and Liang, F.S., 2004. Small molecules targeting severe acute respiratory syndrome human coronavirus. Proceedings of the National Academy of Sciences, 101(27), pp.10012-10017.

[xiii] Wen, C.C., Kuo, Y.H., Jan, J.T., Liang, P.H., Wang, S.Y., Liu, H.G., Lee, C.K., Chang, S.T., Kuo, C.J., Lee, S.S. and Hou, C.C., 2007. Specific plant terpenoids and lignoids possess potent antiviral activities against severe acute respiratory syndrome coronavirus. Journal of medicinal chemistry, 50(17), pp.4087-4095.

[xiv] McCutcheon, A.R., Roberts, T.E., Gibbons, E., Ellis, S.M., Babiuk, L.A., Hancock, R.E.W. and Towers, G.H.N., 1995. Antiviral screening of British Columbian medicinal plants. Journal of Ethnopharmacology, 49(2), pp.101-110.

[xv] Jassim, S.A.A. and Naji, M.A., 2003. Novel antiviral agents: a medicinal plant perspective. Journal of applied microbiology, 95(3), pp.412-427.

[xvi] Luo, H., Tang, Q.L., Shang, Y.X., Liang, S.B., Yang, M., Robinson, N. and Liu, J.P., 2020. Can Chinese medicine be used for prevention of corona virus disease 2019 (COVID-19)? A review of historical classics, research evidence and current prevention programs. Chinese Journal of Integrative Medicine, pp.1-8.