Malaria is still a big killer across the globe, especially in more tropical climes. Now signs of resistance are beginning to show. From Scientific American:

The malaria parasite is a wily organism, shifting its life stages as it flits from human to mosquito and back again. It still kills some 600,000 people each year and has outwitted eradication efforts, having developed resistance to previously popular drugs and, thus far, eluded vaccine-induced immunity.

The arrival of a powerful drug in the late-20th century gave researchers new hope. Called artemisinin and based on a traditional Chinese herbal remedy, it cleared the parasite faster and more thoroughly than any other current antimalarial. Researchers are still somewhat uncertain about exactly how it works, but they know that it targets the parasite as it infects red blood cells.

But the hope that artemisinin would serve as a final, exterminanting blow against malaria has begun to fade. Since 2008 patients in Southeast Asia have been slower to lose the malaria parasite Plasmodium falciparum than they once were. And this precursor to resistance seems to be spreading, despite efforts to carefully use artemisinin (by giving it in combination with other drugs) to avoid the emergence of resistance.

Science magazine has a report on the development of drug-resistant malaria on its website.