Modern-day pirates are raiding the world's rain forests .

The so-called bio-pirates are scientists who hope to make a fortune by finding herbs with medical properties, and selling the patents to drug companies.

But the native people - whose knowledge they steal - get nothing.

To stop this exploitation, the Brazilian Government is considering legislation to prosecute the bio-pirates.

A team of scientists, on a biological mission in the name of science also try to track the bio-pirates.

The researchers from Acre State University, northern Brazil, check whether foreign bio-pirates are at work.

Their beat is a vast swathe of the Amazon jungle that boasts thousands of rare, often unique, plant and animal species.

Hunting for strangers

Tomas Ludewigs, from the university, says: "We have a wonderful forest full of bio-diversity and people use these wonderful trees for getting their resources.

Forest dwellers know the medicinal secrets of the plants

"But nowadays we have another problem - the bio-pirates are coming in and using those materials."

His team make contact with people living in the forest, in sparsely scattered huts, to find out if any strangers have been seen.

Mr Ludewigs said: "We ask about people coming into the forest, and what they bring in or take out."

A century ago the rubber tree became a classic victim of bio-piracy.

The tree grew only in the Amazon jungle until a British scientist stole the seeds and shipped them out to start vast rubber plantations in the far east.

Some say Brazil still has not learned the lesson.

Medicinal properties

Those living in the forest have a back garden like no other.

Acre University studies the forest in the name of science

Generations before them have gathered the sprigs and leaves that keep them healthy in a place where once outside help was unknown and is still a world away.

They have their own remedies for every ailment.

A few Amazonians, like Paolo the medicine man, seem to know the medicinal properties of every plant in the jungle. Mr Ludewigs' scientists listen attentively.

But they fear a more exploitative interest. "One plant can be used to treat snake bites. That is the kind of product that can be useful for drug companies - for making and developing commercial uses for it," says Mr Ludewigs.

Science vs cash

At Acre University, researchers experiment with the rainforest's bio-diversity in the cause of science. But for laboratories across the developed world the cause is cash.

Scientists at Acre work on a snake

Professor Laembert dos Santos, of the Campinas University, is just one ecologist who claims Brazil is not trying to protect its flora and fauna.

He said: "I think the battle will be lost because the Brazilian government is not interested in indigenous peoples and the protection of knowledge, and, I would say, not even the whole issue of bio-diversity.

"The Brazilian government is interested in how to best sell the genetic resource."

Taking steps to stop pirates

Acre state is taking steps of its own to stop bio-piracy.

Acre has launched the first ever legal case against an Austrian scientist who, it says, catalogued seeds and tree bark used in Indian cures and sold them abroad.

The charge is stealing knowledge from indigenous people.

The state is also trying to push a tough new bio-diversity law through Brazil's national parliament.

But it is paddling against the tide. For the bio-technology industry, the tropics of the world are a source of immensely profitable materials.

And along the banks of the Amazon basin the bio-pirates can hunt their modern-day treasure with little fear of being tracked.

So far the government of Brazil has taken no real measures to deter them. For now the drug and biotechnology giants of the developed world can only expect richer pickings.