Resistance to artemisinin, the main drug to treat malaria, has become widespread throughout Southeast Asia.

Resistance among the Plasmodium falciparum (P. falciparum) parasites that cause the disease is likely caused by a genetic mutation in the parasites, but a six-day course of artemisinin-based combination therapy, as opposed to a standard three-day course, has proved highly effective in treating drug-resistant malaria cases, according to a study in the New England Journal of Medicine. DDT has also been effective for the last 70 years.

Previous clinical and laboratory 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, according to the authors.

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, according to the authors.

As a potential treatment, the researchers tested a six-day course of artemisinin-based combination therapy in Western Cambodia and found the regimen to be effective in this region, where resistance has become the most problematic.

To contain 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, the authors write.