The World Health Organization is warning people not to use only one drug to treat malaria . That drug is artemisinin. W.H.O. officials say people should take it only in combination with other malaria drugs. The fear is that artemisinin could lose its effectiveness if it is misused.

Arata Kochi is the new director of the malaria department at the W.H.O., the United Nations health agency. He says: "If we lose artemisinin, we will no longer have an effective cure for malaria." And if that happens, he says, it might take at least ten years before a new one could be discovered.

Drug combinations are also used to treat diseases like AIDS and tuberculosis. Experts say combination treatments are not only more successful than single-drug, or monotherapy. They also slow the development of resistance to medicines. The organisms that cause malaria have already developed resistance to many other drugs.

The W.H.O. has called on eighteen drug manufacturers to immediately halt the sale of artemisinin by itself. The companies are in China, India, Vietnam and other countries.

The health agency cannot force them to obey. But there are steps it could take to pressure companies that continue to sell artemisinin as a monotherapy. For example, the W.H.O. could urge the World Bank, the Global Fund and other agencies not to buy drugs from those companies.

Artemisinin comes from a plant called the sweet wormwood. Chinese researchers discovered it more than thirty years ago. The W.H.O. says artemisinin is more than ninety-five percent effective in curing malaria when used correctly with other anti-malarial drugs.

Doctor Kochi says there have been no documented cases yet where treatment failed because of resistance to artemisinin. But he says there is concern about decreased reaction to the drug in Southeast Asia. That area is traditionally where resistance to anti-malaria drugs has first appeared.

Malaria produces high body temperatures and a dangerous loss of fluids. The W.H.O. estimates there are more than three hundred million cases of malaria in the world each year. At least one million people die. Nine out of ten deaths happen in African countries south of the Sahara Desert. Most of the victims are young children.

This VOA Special English Development Report was written by Jill Moss. Read and listen to our reports at voaspecialenglish.com. This is Shep O'Neal.