New York, Feb 11 (IANS): Two common wild plants contain extracts that inhibit the ability of the virus that causes Covid-19 to infect living cells, a US study has discovered.

In laboratory dish tests, extracts from the flowers of tall goldenrod (Solidago altissima) and the rhizomes of the eagle fern (Pteridium aquilinum) each blocked SARS-CoV-2 from entering human cells.

The active compounds are only present in miniscule quantities in the plants.

It would be ineffective, and potentially dangerous, for people to attempt to treat themselves with them, the researchers from Emory University in the state of Georgia stressed. In fact, the eagle fern is known to be toxic, they warned.

"It's very early in the process, but we're working to identify, isolate and scale up the molecules from the extracts that showed activity against the virus," said Cassandra Quave, senior author and associate professor in Emory School of Medicine's Department of Dermatology and the Centre for the Study of Human Health.

"Once we have isolated the active ingredients, we plan to further test for their safety and for their long-range potential as medicines against Covid-19," Quave said in the study published in Scientific Reports journal.

Given that Covid-19 is a newly emerged disease, the researchers took a broader approach. They devised a method to rapidly test more than 1,800 extracts and 18 compounds from the Quave Natural Product Library for activity against SARS-CoV-2.

"We've shown that our natural products library is a powerful tool to help search for potential therapeutics for an emerging disease," said Caitlin Risener, a PhD candidate in Emory's Molecular and Systems Pharmacology graduate programme.

Additional experiments showed that the protective power of the plant extracts worked across four variants of SARS-CoV-2: Alpha, theta, delta and gamma.

"Our results set the stage for the future use of natural product libraries to find new tools or therapies against infectious diseases," Quave said.