As a TIME correspondent in Mexico, India, Pakistan and other countries where rogue germs abound, Tim McGirk has had his share of firsthand epidemiological experience. But dengue fever holds a special, painful place in his memory. "There's a reason they call it break-bone fever," says McGirk, who contracted the virus in New Delhi and suffered for three weeks. "You feel like there's this deep, painful itching happening inside your bones. You're on this horrible roller-coaster ride of hot spells and chills, like you're being shaken around. It just racks your body."
Millions of others are being taken on...