Green tea, chokeberry juice, and pomegranate juice killed flu and SARS-CoV-2 viruses when incubated with the viruses in vitro. Thus, oral rinsing using these might be effective in preventing COVID-19.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus causing the global pandemic COVID-19, affects the respiratory tract. It has high transmissibility even before symptoms are seen, making for extremely rapid spread.
The virus initially infects the upper respiratory tract, entering the body mainly via the nose and throat, causing respiratory symptoms such as sore throat and coughing. A few recent studies have reported gargling with commercial mouthwashes may reduce infection and virus spread.
Many natural products have also been purported to have antiviral activity. For example, pomegranate and black chokeberry extracts have been reported to have in vitro activity against the flu virus, and gargling with green tea lowered flu infections. Thus, it would be useful to investigate broad-spectrum antiviral activity of natural products that could curb the spread of respiratory viruses and are inexpensive and easy to adopt.
Virucidal activity of natural products against MVA, IAV, SARS-CoV-2, and AdV5. MVA, IAV (A/H1N1/Brisbane/59/2007), SARS-CoV-2 (BetaCoV/France/IDF0372/2020), or AdV5 (adenoid 75) were incubated with the plant-derived products for indicated contact times before serial titration and inoculation of target cells. Viral titers were determined by monitoring the cytopathic effect and calculated as tissue culture infectious dose 50 (TCID50) according to Spearman-Kaerber. The lower limit of quantification (LLOQ) is defined by the limit of titration (dotted line) or the cytotoxicity of the compound (#). Error bars indicate standard deviation and italics above corresponding bars the decrease of titers compared to control.
Natural products effective at inhibiting SARS-CoV-2
Researchers from the Institute of Molecular Virology, Ulm University Medical Center, Technische Universitaet Dresden and CogniVerde GmbH report the effect of green tea and black chokeberry, pomegranate, and elderberry juices on preventing viral infections in cells. For their study, published on the preprint server bioRxiv*, the authors used Vero E6 cells to test vaccinia virus, influenza A virus, adenovirus type 5, and SARS-CoV-2.
The team mixed the herbal substances with the viruses, incubated them at room temperature, and determined infectivity using tissue culture infectious dose 50 (TCID50) endpoint titration.
After a 5-minute incubation with the herbal substances, they found that chokeberry juice decreased infectivity almost 3,000 times compared to a control with only a buffer. The elderberry juice, pomegranate juice, and green tea decreased infectivity by about ten times. An increase in incubation time to 20 min increased the activity only marginally, indicating the antiviral activity is rapid. This suggests that the herbal extracts are generally active against enveloped viruses.
When the researchers tested the swine flu virus (IAV) and SARS-CoV-2, they found the four herbal substances inactivated more than 99% of IAV after 5 minutes.
Chokeberry juice inactivated about 97% of SARS-CoV-2 after 5 min, while green tea and pomegranate juice inactivated about 80% of the virus. Elderberry juice had no effect on SARS-CoV-2. The naked AdV 5, used as a control, was resistant to all except chokeberry juice.
IAV was the most susceptible to the food products, which showed virucidal activity similar to those of typical disinfectants, indicating the low resistance of this virus family, which is also representative of other influenza strains.
SARS-CoV-2 was more resistant, although chokeberry juice was quite effective, with pomegranate juice and green tea also reducing virus amounts.
Oral rinsing using tea and juices
The activity of herbal products could be because of their acidic pH, which can directly inactivate viruses, or because of the presence of polyphenols such as catechins, tannins, and flavonoids, which can affect viral proteins.
For example, polyphenols in pomegranates have been shown to inhibit flu virus by affecting the surface glycoproteins and damaging the structural proteins. Catechins, which are found in green tea, can affect both the virus particles and their binding to host cells. Computer simulations have suggested theaflavins might prevent SARS-CoV-2 infection by binding to the angiotensin-converting enzyme 2 (ACE2), the receptor that binds to SARS-CoV-2.
For respiratory viruses, since the infection and transmission occurs via the nose and throat, reducing viral loads early may be an effective strategy for reducing and preventing spread.
For example, herbal products, like the ones discussed, are commonly available and are used as foods. They could be used as “oral rinses.” In contrast to antiseptic oral rinses that have agents that damage membranes, these juices and tea can be used more frequently without any adverse effect and can be simply swallowed.
Studies have shown that gargling with tea, tea extracts, or plant juices can lower flu infections and viral symptoms. Similarly, chokeberry or pomegranate juices could be used against SARS-CoV-2, in addition to teas.
Continued gargling and rinsing the mouth with juices and teas followed by swallowing could be an effective preventive strategy for SARS-CoV-2, write the authors, particularly for people at high risk of infection healthcare workers and the elderly. Swallowing the “oral rinse” is also practical in situations like on planes, trains, and schools, apart from being healthy in general.
Although the amounts of the different antiviral compounds in natural products may vary with different produce batches, natural products with their mix of compounds may be a powerful method of curbing viral infections and there is a need for further clinical investigations.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.