In May 1993, a fit young Navajo man was rushed to a New Mexico hospital complaining of breathing problems. Within hours, he was dead. Soon others became infected and died as well. With a mortality rate of 70 percent, the outbreak was especially terrifying. Eventually, it was identified as a type of hantavirus, an infection carried by rodents--in this case deer mice. This discovery allowed people to take preventative measures by keeping their homes...