Wellcome researchers reporting in The Lancet found a strain of the malaria type called Plasmodium falciparum that is resistant to the most effective treatment drugs. This has spread widely through parts of Thailand, Laos and Cambodia.
Further spread, to India and Africa, would result in a global public health emergency warns the research team.
The study was led by researchers at the Mahidol-Oxford Tropical Medicine Research Unit (MORU), the Mahidol University in Bangkok, Thailand, and Oxford University, UK.
Professor Sir Nicholas White, of Mahidol and Oxford universities, says: "The spread and emergence of drug-resistant malaria parasites across Asia into Africa has occurred before. Last time it killed millions. We need to work with our policy, research and funding partners to respond to this threat in Asia urgently to avoid history repeating itself."
The mutant malaria parasites were identified through examination of blood spot samples from patients with falciparum malaria from sites in Cambodia, Laos, Thailand and Myanmar.
The team found one strain of resistant parasite – PfKelch13 C580Y – which appears fitter, more transmissible and is spreading more widely than other mutant malaria strains.
The study was funded by Wellcome and the Bill & Melinda Gates Foundation.
Data to help track resistance to drugs, like this study, is vital for improving treatment, diagnosis and prevention of drug-resistant infections.
Prof White played a key role in the global recommendation of artemisinin-based combination therapy as the most effective treatment for malaria caused by the Plasmodium falciparum parasite. This has led to a major reduction in deaths and illness from the disease.