BACKGROUND : Influenza infection remains a major health threat for animals and humans which crucially requires
effective antiviral remedies. The usage of herbal medications as readily available alternatives for their compatibility
with the body and fewer side effects compared to synthetic chemical treatments has become popular globally.
The aim of this study was to investigate and screen in vitro anti-influenza activity of extracts of five South African
medicinal plants, namely Tabernaemontana ventricosa, Cussonia spicata, Rapanea melanophloeos, Pittosporum
viridiflorum and Clerodendrum glabrum, species which are used traditionally for the treatment of several diseases
such as inflammatory and respiratory diseases.
METHODS : Methanol, ethanol (100% and 30%), acetone, hot and cold water extracts of the powdered plants leaves
were obtained by standard methods. The cytotoxicity was determined by the MTT colorimetric assay on MDCK
cells. The concentrations below CC50 values were tested for antiviral activity against influenza A virus (IAV) in
different combination treatments. The effect of extracts on viral surface glycoproteins and viral titer were tested by
HI and HA virological assays, respectively.
RESULTS : Based on the applied methods, the most effective results against IAV were obtained from Rapanea
melanophloeos methanol leaf extract (EC50 = 113.3 μg/ml) and Pittosporum viridiflorum methanol, 100% and 30%
ethanol and acetone leaf extracts (EC50 values = 3.6, 3.4, 19.2, 82.3 μg/ml, respectively) in all types of combined
treatments especially in pre- and post-penetration combined treatments with highly significant effects against viral
titer (P ≤ 0.01).
CONCLUSION : The outcomes offer for the first time a scientific basis for the use of extracts of Rapanea melanophloeos
and Pittosporum viridiflorum against IAV. It is worth focusing on the isolation and identification of effective active
compounds and elucidating the mechanism of action from these species. However, Tabernaemontana ventricosa,
Cussonia spicata and Clerodendrum glabrum leaf extracts were ineffective in vitro in this study.
Additional file 1: Figure S1. Estimated Marginal Means of Log HA titer.
This graph shows the Log HA titer levels analyzed by GLM.
Additional file 2: Figure S2. Estimated Marginal Means of Log HA
decrement. This graph shows the decrement levels in Log HA titers
analyzed by GLM.
Additional file 3: Figure S3. Estimated Marginal Means of cell viability.
This graph shows the ODs of the cell viability test analyzed by GLM.
Additional file 4: Figure S4. Estimated Marginal Means of percentage
of protection. This graph shows the protection of the extracts on the cell
viability analyzed by GLM.