Parasites resistant to the frontline malaria drug have spread westward from southeast Asia to just short of the Indian border -- a gateway to Africa, researchers warned Friday.
A spread into India "would pose a serious threat to the global control and eradication of malaria," said a statement that accompanied the study published in The Lancet Infectious Diseases.
"If drug resistance spreads from Asia to the African sub-continent, or emerges in Africa independently as we've seen several times before, millions of lives will be at risk."
Since the Plasmodium parasite developed resistance to other drug types, artemisinin is the best and safest medicine to treat the estimated 198 million malaria infections that occurred worldwide in 2013.
There were about 584,000 deaths, according to the UN's World Health Organization (WHO) -- 90 percent of them in Africa.
Artemisinin resistance has not yet been detected in Africa, but is a growing problem in southeast Asian nations like Cambodia, Thailand and Vietnam, and is suspected, though not proven, to have taken hold in South America.
Myanmar, which carries the region's highest malaria burden, is considered the parasite's main route from southeast Asia to India and beyond.
-- International effort needed --
For the study, researchers collected samples from patients at 55 treatment centres across Myanmar and border regions of Thailand and Bangladesh in 2013 and 2014, and examined them for telltale mutations in the K13 or "kelch" gene.
Thirty-nine percent of 940 malaria samples carried a mutation, they found.
The team then used the data to produce a map of estimated regional prevalence, and predicted resistance as far west as Homalin in Myanmar -- 25 kilometres (15.5 miles) from the frontier with India.
"This study highlights that the pace at which artemisinin resistance is spreading or emerging is alarming," said study co-author Philippe Guerin, director of the Worldwide Antimalarial Resistance Network.
"We need a more vigorous international effort to address this issue in border regions."
The malaria parasite is transmitted via the bites of infected mosquitoes.
It multiplies in the human liver and infects red blood cells, and can be deadly if untreated.
There have been two examples in history of malaria drugs becoming less effective due to the emergence of resistance -- costing millions of lives.
From the 1950s to 1970s, chloroquine-resistant parasites spread from Asia to Africa.
Chloroquine was replaced by sulphadoxine-pyrimethamine (SP), resistance to which emerged in western Cambodia and spread to Africa.
SP was then followed by artemisinin, a drug derived by Chinese scientists from a herb called sweet wormwood.
- Thousands at risk -
"The new research shows that history is repeating itself with parasites resistant to artemisinin drugs, the mainstay of modern malaria treatment, now widespread in Myanmar," said Mike Turner of the Wellcome Trust which co-funded the study.
"We are facing the imminent threat of resistance spreading into India, with thousands of lives at risk."
The team stressed there was no evidence that artemisinin resistance has indeed reached India, "however, few data are available".
The WHO has recommended artemisinin-only treatments be withdrawn from the market in favour of combination therapies to protect against the spread of resistance, but they remain available in many countries.