For decades, doctors have been unable to answer the most basic question about Kawasaki disease: what causes it — a virus, a chemical, a fungus? Whatever it is, it provokes mysterious swelling and rashes in infants. Doctors now think they have finally figured out what causes Kawasaki — thanks to an analysis of the wind.
Kawasaki disease is most common in Japan, but it occasionally crosses the Pacific to sicken babies on the west coast of the United States. Infants are beset with a strange combination of symptoms including swollen arms and legs, rashes, irritated eyes and a characteristic strawberry tongue. One in 100 will die.
Several years ago, with Kawasaki research at an impasse, Xavier Rodó began plugging the incidence of the disease into climate models, checking against temperature, precipitation and humidity. Then he hit upon something: wind patterns. When strong winds blew across central Asia to Japan, Kawasaki broke out. When those same winds blew thousands of miles across the Pacific, the disease broke out in the US too.
In a new paper this week, published in the journal PNAS, Rodó's presents even more evidence of how Kawasaki spreads across Japan's cities during these winds.
Aerial view of Tokyo during a sampling flight. Image courtesy of Roger Curcoll.
These correlations are fine and all, but what is actually in the wind? On a March day four years ago, a small plane flew above Tokyo into the winds blowing from central Asia. The plane carried fine filters to capture tiny particles in the air. Researchers found these particles to be full of fungal spores, half of them from a fungus called Candida. Candida is known to cause infections in humans, but it's never been found so high up in the air before.
Fungal spores are hardy little things — known to tough out subzero temperatures and ultraviolet radiation. Valley fever is a fungal disease spread by wind in the American southwest. The evidence so far doesn't conclusively finger Candida as the cause of Kawasaki disease, but it's the best candidate out there.
You may be familar with John Snow, who mapped 19th century London streets to trace a cholera outbreak to a single water pump on Broad Street. His work proved that cholera was caused by contaminated water, rather than some general miasma in the air. This sort of mapping is still a basic tool for epidemiologists today. Kawasaki may be the first disease solved by looking at wind patterns. [PNAS via National Geographic]
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