SÃO PAULO, BRAZILIn the Facebook video posted on March 30, a man turns over a small plastic bag he’s holding, filled with tree bark shavings. He shows his followers that it’s labeled “quina tea” and explains how to prepare the drink he says will “immunize your body and fight COVID-19.”

The demand for the tea will be high, he says, and he urges everyone watching to buy theirs now. He’s not the only one who thinks this way—and that may be a big problem.

As scientists the world over search for a way to prevent and treat COVID-19, some Brazilians have turned to nature for a remedy. They’ve stumbled upon a family of plants known locally as quina, used often in the Amazon and