Now the internal temperature begins to rise as the body attempts to cook away the invaders. Shivering sets in—muscle vibrations generate warmth. This is followed by severe fever, then drenching sweat. Cold, hot, wet; the symptoms are a hallmark of the disease. But the parasites' exponential growth continues, and after a few more cycles there are billions of them tumbling about the blood.

By this point, the fever has reached maximum intensity. The body is practically boiling itself to death—anything to halt the attack—but to no avail. The parasites can even commandeer blood cells to help aid their survival. In some cases of falciparum, infected cells sprout Velcro-like knobs on their surfaces, and as these cells pass through the capillaries of the brain, they latch to the sides. The adhesion keeps them from washing into the spleen, which cleans the blood by shredding damaged cells. Somehow—no one is quite sure how—the adhesion also causes the brain to swell. The infection has turned into cerebral malaria, the most feared manifestation of the disease.

This is when the body starts to break down. The parasites have destroyed so many oxygen-carrying red cells that too few are left to sustain vital functions. The lungs fight for breath, and the heart struggles to pump. The blood acidifies. Brain cells die. The child struggles and convulses and finally falls into a coma.

Malaria is a confounding disease—often, it seems, contradictory to logic. Curing almost all malaria cases can be worse than curing none. Destroying fragile wetlands, in the world of malaria, is a noble act. Rachel Carson, the environmental icon, is a villain; her three-letter devil, DDT, is a savior. Carrying a gene for an excruciating and often fatal blood disorder, sickle-cell anemia, is a blessing, for it confers partial resistance to falciparum. Leading researchers at a hundred medical centers are working on antimalarial medicines, but a medicinal plant described 1,700 years ago may be the best remedy available. "In its ability to adapt and survive," says Robert Gwadz, who has studied malaria at the National Institutes of Health, near Washington, D.C., for almost 35 years, "the malaria parasite is a genius. It's smarter than we are."

The disease has been with humans since before we were human. Our hominin ancestors almost certainly suffered from malaria. The parasite and the mosquito are both ancient creatures—the dinosaurs might have had malaria—and this longevity has allowed the disease ample time to exploit the vulnerabilities of an immune system. And not just ours. Mice, birds, porcupines, lemurs, monkeys, and apes catch their own forms of malaria. Bats and snakes and flying squirrels have malaria.