Antiviral Herbal Approaches

 Posted: March 2020
Author: Phil Rasmussen |  M.Pharm., M.P.S., Dip. Herb. Med.; M.N.I.M.H.(UK),  F.N.Z.A.M.H. 

The outbreak of a new human form of coronavirus (COVID-19) in December 2019 in Wuhan in China, is having a huge impact on many millions of people, initially in China, but increasingly around the world.  While infection with COVID-19 seems less likely to cause death than the SARS virus, it is also highly infectious, with more than 120,000 cases and more than 4,500 deaths from it to date. Most COVID-19-infected patients initially present with fever or cough at the onset of symptoms, and around a third of patients with dyspnoea (shortness of breath). Myalgia (muscle pain) or fatigue also seem to be common symptoms. The main cause of death is from pneumonia and acute respiratory distress syndrome ^{(1, 2)}, with older people and those with pre-existing health conditions such as asthma, cardiovascular disease or diabetes, being most at risk.

While enhancing immunity to help protect against infection is probably the best approach at present⁽³⁾, a brief review of other herbal management options is useful.

Antiviral Herbs

Just as it is challenging for drug developers to make drugs such as oseltamivir, zanamivir and ribavirin with clinically significant antiviral actions, so it is to identify herbal remedies with such properties. While in vitro antiviral actions have been shown against a range of viruses by various phytochemicals, more relevant to medical herbalists is evidence of whole plant preparations which exhibit antiviral activity in vivo.

There are many herbs worth considering for their potential antiviral effects, from either a traditional use perspective, or from studies showing relevant antiviral actions in animal studies.

Some that are worthy of further investigation include Cordyceps militaris, Forsythia suspensa, Zingiber officinale, Lonicera japonica, Scutellaria baicalensis, Sambucus nigra and Nigella sativa.

Cordyceps (Cordyceps militaris) is a traditional medicinal mushroom, and studies in mice have shown it to reduce the severity of acute lung injury, used as a model of acute respiratory distress in humans⁽⁴⁾. Cordycepin, a key nucleoside constituent, also exhibits antiviral activity against several viruses, including influenza, human insufficiency virus, Epstein Barr, Hepatitis C, and murine leukaemia virus^(4-6).

Blackseed (Nigella sativa) is a highly revered traditional remedy used by many ethnic groups to enhance immunity and for a wide range of health issues, including diarrhoea and various types of infections⁽⁷⁾. Protection against murine cytomegalovirus has been reported for blackseed oil, and an Egyptian study found Nigella administration to significantly reduce viral load in patients with Hepatitis C⁽⁸⁾. A combination of Nigella with Echinacea also reduced dexamethasone-induced stress in chickens vaccinated against the H9N2 avian influenza virus⁽⁹⁾.

Elderberry (Sambucus nigra) has traditionally been used to treat influenza and colds, and extracts have exhibited antiviral effects in vitro and on human influenza A-infected mice^(10-12). Inhibitory effects on influenza viral replication have been reported, although relatively large doses seem to be required⁽¹³⁾.

Baical skullcap (Scutellaria baicalensis) is used traditionally for the treatment of colds, fever and influenza, and a key flavonoid constituent baicalin has reported in vitro activity against SARS coronavirus⁽¹⁴⁾. Baicalin and other key flavonoids baicalein and wogonin, also have neuraminidase inhibitory activity, the mechanism of action of antiviral drugs such as oseltamivir⁽¹⁵⁾. A flavonoid enriched extract also reduced acute lung injury induced by influenza A virus in mice⁽¹⁶⁾. Wogonin also has anti-influenza properties via modulation of AMPK pathways⁽¹⁷⁾.

Immune enhancement and modulation, and anti-inflammatory effects are principal actions of Echinacea, and numerous studies have reported immunological changes associated with Echinacea root usage. Suppressive effects have been reported for Echinacea purpurea against spontaneously occurring leukaemia caused by a murine leukaemia virus, an effect related to enhancement of immune systems⁽¹⁸⁾.

Viral infections can also express bacterial adhesion receptors, and invoke an inflammatory response that can disturb the integrity of the respiratory tract’s physical barrier to bacteria. Evidence suggesting Echinacea may prevent virus-induced bacterial adhesion to cell membranes, and moderate an excessive inflammatory response (cytokine storm) which can be a feature of pandemic viruses^{(3, 19,20)}, may therefore contribute to improved host resistance against pathogenic viral infections.

Respiratory Herbs

There are many herbs that may help improve symptoms of or shorten the duration of coughs due to respiratory tract infections, including Kumerahou, Elecampane, Thyme, Bupleurum, Hyssop, Marshmallow, Garlic and Horseradish. These or other herbs traditionally used for congestion or infection of the lungs, may provide relief to some patients, and help lessen the risk of secondary bacterial infections and need for drug-based products.
 

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