As we witnessed during the COVID-19 pandemic, mass viral outbreaks can cause an immense strain on health and wider society. Not wanting history to repeat itself, researchers have been scrambling to find a new antiviral medication and it appears they may have found it in a somewhat unsuspecting place – willow bark.

Looking to nature

The phrase “drug discovery” often conjures up images of high-tech labs and synthetic compounds, but researchers often find inspiration in the natural world. Just over 40 percent of drugs approved between January 1981 and September 2019 stemmed from natural products. 

Willow bark is perhaps one of the most well-known natural medicinal products; it’s been used for centuries to treat pain and inflammation. Its anti-inflammatory properties are thought to be down to the compound salicin, which aided in the development of aspirin. 

Researchers had previously found that extract of the bark was highly effective against enteroviruses – which is a significant discovery considering there are currently no clinically approved drugs that directly target this group of viruses. However, in a new study, scientists have demonstrated that willow bark extract could be used against a wider range of viruses with different structures.

Backing it up with science

The team created an extract from commercially grown willow, by grinding up the bark, putting it in hot water, and sieving it. The solution was then added to cells infected with either Coxsackievirus A or B, both of which are enteroviruses, a seasonal coronavirus, or SARS-CoV-2. The researchers timed how long the extract took to act on the infected cells and how well it managed to inhibit viral activity.

The results showed that willow extract had an efficient antiviral effect on all of the viruses tested, appearing to act on their surface to inhibit infection. The extract’s exact mechanism of action, however, appeared to be quite varied depending on the structure of the virus. 

Some viruses, such as coronaviruses, have an envelope that protects their genetic material during transmission. The researchers found that the coronaviruses appeared to have been broken down by the action of the extract, whereas the non-enveloped viruses were “locked down”, prevented from reproducing.

“The extracts acted through distinct mechanisms against different viruses,” said Varpu Marjomäki, senior author of the study, in a statement. “But the extracts were equally effective in inhibiting the enveloped as well as non-enveloped viruses.”

More research required

The study also involved an analysis of the extract’s chemical composition to try and understand which of the compounds in it may be responsible for the bark’s antiviral properties – this is an important part of drug development. Whilst there were no clear answers in this case, it provides the foundation for future work, according to Marjomäki.

“We are presently continuing fractionations and bioactive molecule identification from willow bark extracts,” said Marjomäki. “This will give us a number of identified pure molecules which we can study in further detail. Also, we will study a larger number of viruses with purified components. Purified components will give us better opportunities to study their mechanisms of action.”

The current study and future work will likely be a core element in how we attempt to combat future viral outbreaks. “We need broadly acting and efficient tools to combat the virus load in our everyday life,” said Marjomäki. “Vaccinations are important, but they cannot deal with many of the newly emerging serotypes early enough to be effective on their own.”

Let’s hope that the humble willow tree can come to our rescue.

The study is published in Frontiers in Microbiology.