BANGKOK — The world’s best drug for treating malaria, a medicine that is the key to saving millions of lives in Africa and beyond, is losing its efficacy in a much larger swath of territory than was previously known, according to research that was to be released Friday.
The study, in The Lancet Infectious Diseases, a medical journal, raises the troubling prospect that resistance to the drug, artemisinin, might one day severely hamper treatment of a disease that kills hundreds of thousands of people every year.
“This should focus minds,” said Charles Woodrow, one of the authors of the study. “We have to eliminate these very resistant parasites. The fear is that if we don’t, we would reverse all the gains that have been made.”
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Drug resistance appears to be most acute in western Cambodia, where a standard three-day course of drugs is no longer effective for many patients, scientists say. Additional doses are needed to mop up the malarial parasites.
Researchers’ great fear is that resistance to artemisinin will spread to Africa. Ninety percent of the estimated 584,000 annual deaths from malaria occur in Africa, according to the World Health Organization.
A version of this article appears in print on February 20, 2015, on page A6 of the New York edition with the headline: Malaria in Widening Area Resists Drug, Study Finds . Order Reprints| Today’s Paper|Subscribe
