The malaria parasites in Southeast Asia are becoming resistant to a key drug, a study warns.
Resistance to artemisinin, the main drug to treat malaria, is now widespread among the Plasmodium falciparum parasites that cause the disease and is likely caused by a genetic mutation in the parasites.
Previous studies suggest that P. falciparum parasites with a mutant version of a gene called K13-propeller are resistant to artemisinin.
In the new study, researchers found that the geographic distribution of these mutant parasites in western Cambodia corresponded with the recent spread of drug resistance among malaria patients in that region.
Although artemisinin continued to effectively clear malaria infections among patients in this region, the parasites with the genetic mutation were eliminated more slowly.
Slow-clearing infections strongly associated with this genetic mutation were found in additional areas, validating this marker of resistance outside of Cambodia.
"Artemisinin resistance is now firmly established in areas of Cambodia, Myanmar, Thailand and Vietnam," authors noted.
However, a six-day course of artemisinin-based combination therapy - as opposed to a standard three-day course - has proved effective in treating drug-resistant malaria cases.
"To contain the further spread of artemisinin resistance, continued geographical monitoring is needed as well as a re-examination of standard malaria treatment regimens and the development of new therapy options," authors wrote.
The findings were published in the New England Journal of Medicine.
