Nowhere on Earth is malaria more threatening than in northwestern Thailand. Here, the deadliest form of the parasite, Plasmodium falciparum, has been toughened by decades of exposure to antimalarial drugs—conditions that promote the survival of drug-resistant strains. In this caldron, says researcher Nicholas White of Bangkok's Mahidol University, a "nightmare scenario" is brewing: Local parasites are becoming resistant to every cheap drug that works. The old standby, chloroquine, "is gone, just about everywhere," agrees Pierro Olliaro of the World Health Organization (WHO), and resistance to newer drugs is emerging.
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