In March 2011, a small research aircraft took off from Japan, and flew into winds blowing in from northeast China. It carried a set of special filters, designed to strain small particles from the air. Among these particles, hopefully, would be the culprit behind Kawasaki disease—an illness whose cause has eluded detection for decades and could, quite literally, be blowing in the wind.

Kawasaki disease was first described by Japanese paediatrician Tomisaku Kawasaki in 1967. It largely affects children under the age of 5. Blood vessels throughout a child’s body become inflamed, leading to a weird constellation of symptoms including swollen hands and feet, red lips, strawberry tongue, irritated eyes, and rashes. If the inflammation affects the arteries of the