TURNING THE TIDE

Some ages are defined by their epidemics. In 1347 rats and fleas stirred up by Tatar traders cutting caravan routes through Central Asia brought bubonic plague to Sicily. In the space of four years, the Black Death killed up to 30 million people. In 1520, Cortes' army carried smallpox to Mexico, wiping out half the native population. In 1918 a particularly virulent strain of flu swept through troops in the trenches of France. By the time it had worked its way through the civilian population, 21 million men, women and children around the world had perished--more than were killed in World...