Antiviral activity of plant juices and green tea against SARS-CoV-2 and influenza virus in vitro

Discussion

We examined and compared the virucidal activities of four natural beverages on a surrogate and three respiratory viruses and found that chokeberry juice, green tea and pomegranate juice reduced infectious titers of enveloped viruses with chokeberry juice being most efficient. The tested food products showed the highest antiviral efficacy against IAV, with ≥ 4 log10, which corresponds to the effectiveness of typical disinfectants. The high susceptibility of IAV (H1N1), which is also a representative of influenza B and other influenza strains with regard to chemical stability, indicates low resilience of this virus family. SARS-CoV-2 behaved similar to the European model virus for enveloped viruses, MVA, and proved to be more resilient. Nevertheless, chokeberry juice inactivated >96% infectivity and pomegranate juice and green tea reduced titers, however, to a lesser extent. Notably, activity against MVA is prerequisite for validation of general disinfectant property of chemicals according to the European Chemicals Agency [11] and suggestive of broad activity against all enveloped viruses. As expected, the non-enveloped adenovirus, was less susceptible to the tested products, however, was also affected by the very potent chokeberry juice. Generally, differences in contact times did not have a strong influence on the efficiency of inactivation suggesting a rapid acting antiviral effect.

The antiviral activities of the plant products can be based on an acidic pH that may directly inactivate virus particles or by (poly-)phenols such as catechins, tannins or flavonoids that can act on viral and cellular proteins [12,13]. For example, pomegranate polyphenols were shown to inhibit influenza viruses by acting on virion surface glycoproteins and causing structural damage to the virion [14]. Similarly, green tea catechins have been shown to destroy the virion structure and epigallocatechin gallate aggregates virus particles to prevent their interaction with target cells [15]. Catechins not only act on the virus particles but have additionally been shown to prevent fusion by interfering with endosome acidification and viral enzymes. For theaflavin-3,3′-digallat computer modelling suggested that it might prevent SARS-CoV-2 infection by interacting with its cellular receptor angiotensin converting enzyme 2 (ACE2) [13,15]. Of note, the composition of natural food products may vary between batches, which might affect their antiviral efficiency. Nevertheless, the composition of various antivirally active components, acting by different mechanisms, represents a potent mix interfering with virus infection.

Since viral replication, symptoms and transmission occur in the naso- and oropharyngeal area, reducing viral titers as early as possible might represent a proactive strategy to prevent infection, dissemination, disease, and spread. The herbal products are common and available food preparations that could be applied as convenient “oral rinses”. Antiseptic oral rinses containing membrane-damaging agents (i.e. ethanol, chlorhexidine, cetylpyridinium chloride, hydrogen peroxide and povidone-iodine) are used in various private or clinical situations for prophylactic and therapeutic purposes and have further been applied in the context of viral infections [4,5]. In contrast to these chemical preparations, green tea and herbal juices can be applied more frequently and may be simply swallowed. Gargling tea, tea extracts or plant juice followed by drinking has already been shown to lower the incidence of influenza virus infections, viral loads and symptoms [8,9]. Similarly, antivirally active plant products such as chokeberry [7] or pomegranate [6] juice might be translated into “clinical” use against influenza viruses and SARS-CoV-2.

In the case of SARS-CoV-2, the virus may be passed before symptom onset, which is particularly treacherous. Oral rinsing and gargling with the tested juices and tea are largely unproblematic in long-term use and might be a suitable pre- and postexposure prophylaxis against SARS-CoV-2 during the current COVID-19 pandemic for any individual but especially those with high risk of infection or severe disease including healthcare workers, elderly, or immunocompromised. Additionally, the possibility of swallowing the “oral rinse” is practical in many situations such as during a flight, train or car ride, in day-care centres or schools and can even be part of a healthy diet. Furthermore, it would be helpful to reduce the risk of transmission in school classes and children by using nutritionally valuable and healthy food products instead of aggressive disinfectants or obstructive measures.

Thus, the administration of chokeberry juice, pomegranate juice or green tea may offer a possibility to minimize the spread of enveloped respiratory viruses, ease symptoms and potentially contribute to disease prevention and clinical investigation of their benefits is warranted.