A form of malaria that is resistant to standard treatment has spread to Vietnam for the first time, researchers warned Friday.
The strain was originally detected in Cambodia in 2007, and experts are calling for action before it reaches other areas such as India or Africa.
"It spread like a wildfire to Vietnam," Professor Arjen Dondorp, head of malaria department at the tropical medicine research unit at Mahidol University in Bangkok, told AFP.
The co-author of an article published on Thursday in the medical journal The Lancet Infectious Diseases added: "It started 10 years ago in western Cambodia. It is very fit and spreads very easily. This resistance is taking over.
"Cambodia already changed to a new drug, likely to last one or two years. Vietnam has to change now."
After its detection in western Cambodia in 2007, the strain then spread to northeastern Thailand, southern Laos and eastern Myanmar, a previous study by Dondorp and colleagues said.
"The fear is that it spreads further, to India and Africa," warned Dondorp.
The standard frontline choice for treating malaria is artemisinin in combination with another drug. The parasite mutation spotted by Dondorp's team notably confers resistance to the drug piperaquine.
According to the World Health Organization (WHO) there were at least 212 million cases of malaria in 2015 and 429,000 deaths. The disease is caused by parasites transmitted to people through the bites of infected female mosquitoes.
For specialists, the emergence of the new strain in Southeast Asia is worrying, even though the number of cases is limited.
Two waves of malaria resistant to standard treatments appeared in the 1950s and 60s in Southeast Asia and spread to India and Africa, where they caused millions of deaths.
Dondorp chairs the steering committee for a large regional malaria grant from the Global Fund, a financing organisation, in Thailand, Cambodia, Vietnam, Laos and Myanmar with a budget of $243 million (203 million euros) over the next three years.
He advocates treatment at an early stage of the disease, which will require community malaria workers in even the most remote areas at risk.