Scientists Go to the Bush to Find TB Cures

Walter H. Lewis admits he’s surprised himself at the astonishing discovery he and his colleagues made in the Upper Amazon region of the Peruvian rain forest.

For a couple of decades, Lewis has studied Indians who inhabit that lush region because of their legendary use of local plants to fight off diseases.

In recent years Lewis, a professor of biology at Washington University in St. Louis, has focused his research more and more on tuberculosis, which kills about 2 million people a year around the world and has become increasingly resistant to pharmaceutical drugs.

And as one who has developed a profound respect for the medicinal cures of the Aguaruna Indians, Lewis began to wonder if those folks might have a cure for TB.

At first blush, that doesn’t make much sense. Except for rare occurrences, the relatively isolated Indians of the Upper Amazon don’t have a significant problem with TB, so they have no need to find plants that would fight a disease they rarely see. Virtually all of their tribal cures are targeted for specific diseases.

But still, Lewis couldn’t help but wonder. These were the people, after all, who are believed to have been the first to find that quinine bark could help fight off the ravages of malaria. And the poison darts they used for hunting yielded a drug that proved extremely valuable as a muscle relaxant.

Today, “it is probably used in every major surgery,” Lewis says.

Memory Elvin-Lewis, his wife and partner, who is also a professor of biology at Washington University, was equally impressed by the accomplishments of the Aguaruna. Years earlier, while she was a professor in the university’s dental school, she became fascinated by the fact that the Indians had black teeth.

During their many trips to the Upper Amazon, Elvin-Lewis learned why. The Indians chewed on leaves and the fruit of a plant that turned their teeth black. But it also did something else. It sealed the enamel of their teeth and prevented decay, and it coated their teeth with fluoride centuries before modern toothpaste brought that preventive medicine to the rest of us.

So four years ago the couple returned to the rain forest to see if the magical cures used by the Indians could also help curb a frightening rise in tuberculosis.

“It was just an intuitive guess at that time,” Lewis says.

Long, Laborious Task

They returned home with extracts from about 1,250 plants used as medicine by the Aguaruna. Then they began the long, laborious task of determining which might be too toxic to be of any value, and which might contain some compound that would be helpful in the fight against TB. It’s not surprising that none of them have proved particularly toxic, because the Indians would not have been using them if they had made them ill. But laboratory tests showed that some extracts from the sample inhibited the growth of Mycobacterium tuberculosis, the bacterium that causes TB.

“That was surprising,” Lewis says.

And it wasn’t just a few. A whopping 46 percent of the extracts contained something that inhibited the growth of the TB cells, possibly pointing the way to new drugs that could help control an epidemic that kills more people every year than any other infectious disease.

Lewis and his collaborators, including Scott Franzblau at the Federal Hansen Laboratory at Louisiana State University, are now trying to narrow down which specific compound, or combination of compounds, in the extracts is doing the job.

The process involves discarding compounds that seem to be irrelevant, then dividing those that work into smaller units, and running the tests again, narrowing the field down with each step. So far, the researchers have found three compounds that block the formation of the bacteria’s cell wall, causing it to die.

“We have three wonderful hits,” Lewis says.

But why would these plants of the Upper Amazon contain a compound that destroys tuberculosis cells when TB is not much of a problem in that isolated area?

Lewis has a hypothesis.

“These trees and plants are growing in a rain forest and are subjected to a huge amount of stress all the time,” he says. “They have to constantly protect themselves against being infected by microorganisms and eaten by insects. That’s morning, noon and night, 12 months out of the year.”

Lewis found his most important clue in the soils around the plants. The soils are rich with bacteria “that are extremely close, in the same bacterial family,” as the one that causes TB.

These microorganisms, he says, won’t cause TB in humans, but their presence forces the plants and trees to produce compounds that can fight off the bacteria.

So it may well be that plants in the Peruvian forest are producing compounds for their own protection that could, in the end, save millions of lives.

It will be years before we really know that, of course. There is much more research to be done, and then lengthy clinical trials will have to show that the compounds work, and are safe, before pharmaceutical drugs can be marketed.

“We just don’t know, at this stage, but it’s intriguing,” says Lewis.

If it all pans out, the younger natives of the Upper Amazon, who were drifting away from their tribal cures, will have one more reason to believe in the wisdom of their elders.

It is, after all, the old folks that the “strange people” like him have come so far to see, Lewis says. They are the ones who have passed on this knowledge from generation to generation. They have known what works, for hundreds of years.

Maybe they can help us again.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.