New York  - The global fight against malaria was threatened by the emergence of drug-resistant strains on the Thai-Cambodia border, the World Health Organization said Wednesday.

WHO said artemisinin-resistant parasites could infect workers clearing forests along that border and create a form of drug- resistant malaria. Such a development could set back recent successes in controlling the disease.

Artemisinin is an extract of a Chinese herb that is used in the treatment of several diseases, including malaria.

The Geneva-based UN health agency said an estimated 1 million people die annually from malaria, one of the world's major killer diseases. Strong malaria control programmes have helped lower infection and death rates in recent years.

But WHO said drug-resistant parasites could pose a major obstacle to malaria control efforts. It said drug resistance increases with the use of single-drug therapy for malaria, such as monotherapies of artemisinin and its derivatives, and called for removing them from the market.

"We know that malaria can be treated and prevented," said Regina Rabinovich, director of the infectious disease programme at the Bill and Melinda Gates Foundation. "If we lose the key treatment available at this time, it's like living in a house with a half roof."

The foundation has donated tens of millions of dollars to anti- malaria programmes worldwide.

"If we do not put a stop to the drug-resistant malaria situation that has been documented on the Thai-Cambodia border, it could spread rapidly to neighbouring countries and threaten our efforts to control this deadly disease," said Hiroki Nakatani, WHO assistant director- general.

WHO said resistance to anti-malaria drugs at the Thai-Cambodia border began with chloroquine, followed by resistance to sulfadoxine- pyrimethamine and mefloquine, which have been used in malaria control for many years. (dpa)