Drug-resistant malaria parasites have moved from Cambodia to Laos, Thailand and Vietnam, where half of patients are not being cured by first-choice drugs, researchers from the UK and Thailand say.
Researchers say the findings raise the “terrifying prospect” drug-resistance could spread to Africa.
However, experts said the implications may not be as severe as first thought.
Malaria is treated with a combination of two drugs – artemisinin and piperaquine.
The drug combo was introduced in Cambodia in 2008.
However, by 2013, the first cases of the parasite mutating and developing resistance to both drugs were detected, in western parts of the country.
The latest study, published in the Lancet Infectious Diseases, analyzed blood samples from patients across South East Asia.
Inspecting the parasite’s DNA showed resistance had spread across Cambodia and was also in Laos, Thailand and Vietnam.
The parasite had also picked up further mutations, making it even more problematic.
In some regions, 80% of malaria parasites were drug resistant.
However, it doesn’t mean the disease is becoming untreatable.
A second study, published in the Lancet, showed half of patients were not being cured with standard therapy.
However, there are alternative drugs that can be used instead.
That could include using different drugs alongside artemisinin or using a combination of three drugs to overcome resistance.
Huge progress has been made towards eliminating malaria. However, the development of drug resistance threatens that progress.
The other issue is if the resistance spreads further and reaches Africa, where more than nine in 10 cases of the disease are.
The findings will not change much in people’s day-to-day life in the Greater Mekong Subregion, in South East Asia.
Tackling malaria is about more than just picking the right treatment after an infection.
All the efforts around controlling the mosquitoes that spread the disease will not change.
However, the researchers say the drugs people are given after an infection should change.
The studies also show genetic analysis of malaria parasites can help doctors keep one step ahead of emerging drug-resistance in order to give patients the right treatment.
The spread of resistance is set against the backdrop of falling cases in the region.
In Cambodia there were 262,000 cases of malaria in 2008 and 36,900 in 2018.
There are about 219 million cases of malaria around the world each year.
Symptoms include cycles of feeling cold and shivering followed by a high temperature with severe sweating.
Without treatment, the parasite can lead to breathing problems and organ failure.
Malaria kills about 435,000 people every year – most of them are children under the age of five.