Resistance to new anti-malarial medication appears to be spreading beyond the western Cambodia area where it was first detected, according to a US health official.
The World Health Organization (WHO) warned early last year that parasites resistant to the drug artemisinin had emerged along the border between Cambodia and Thailand.
Artemisinin-based medication has been largely credited in recent years with increasing recovery rates from the mosquito-transmitted disease that kills nearly one million people a year worldwide.
Timothy Ziemer, the US government's global coordinator against malaria, said that after first being spotted in western Cambodia in 2007, "there are now indications of artemisinin resistance in other parts of the region".
Signs of resistance to artemisinin had been found in southern Myanmar and possibly on the Chinese-Myanmar border, and in southern Vietnam near Cambodia, the retired rear admiral told a regional conference that ended Friday.
The WHO warned last year that emergence of the resistance could "seriously undermine" efforts to bring malaria under control.
Artemisinin-based medication was regarded as a replacement for older drugs that were fast becoming useless in several areas of the world as the malaria parasite developed resistance to them.
Ziemer said the number of malaria cases had still fallen. In Vietnam, for example, they were down from about 190,000 in 1991 to 15,000 by 2008, he said.
"But it is essential that national governments remain focused to contain and eventually eliminate these multi-drug resistant strains," he told the conference on international cooperation against infectious diseases.
Important to that strategy is the elimination of fake and substandard medicines, which increase resistance, he said in a speech Thursday.