Drug-resistant malaria superbugs have taken hold in parts of Thailand, Laos and Cambodia, threatening to undermine progress against the disease, scientists say.
The superbugs - malaria parasites that can beat off the best current treatments, artemisinin and piperaquine - have spread throughout Cambodia, with even fitter multi-drug resistant parasites spreading in southern Laos and north-eastern Thailand.
"We are losing a dangerous race to eliminate artemisinin resistant ... malaria before widespread resistance to the partner antimalarials makes that impossible," said research co-leader professor Nicholas White.
"The consequences of resistance spreading further into India and Africa could be grave if drug resistance is not tackled from a global public health emergency perspective."
More than half the world's people are at risk of malaria infection. Most victims are children under five living in the poorest parts of sub-Saharan Africa.
Recent progress against the mosquito-borne disease has been dramatic and numbers falling ill have been significantly reduced, but it still kills more than 420,000 people each year, the World Health Organisation says.
Malaria specialists worldwide say emerging drug resistance in Asia is now one of the most serious threats to that progress.
"We now see this very successful resistant parasite lineage emerging, outcompeting its peers, and spreading over a wide area," research co-leader Arjen Dondorp from the Mahidol Oxford Tropical Medicine Research Unit said.
Efforts to control malaria in Asia must be stepped up urgently "before it becomes close to untreatable".
In their study in the Lancet Infectious Diseases journal, the scientists said that after examining blood samples from malaria patients in Cambodia, Laos, Thailand and Myanmar, they found that a mutation of the disease had spread across countries and replaced other strains.
They explained that while the C580Y mutation does not necessarily make the parasite more drug-resistant, it does have other qualities that make it more risky - notably it appears to be fitter, more transmissible and able to spread more widely.
