Know Your Enemy

The threat of tuberculosis is not a new one. Traces of the disease have been found in ancient mummies, and in the mid-1800s the ailment—then known as consumption—accounted for up to a quarter of the deaths in London, New York, and Paris.

A turning point in people's relationship to consumption occurred in 1882 when the microbiology pioneer Robert Koch showed that the rod-shaped bacterium Mycobacterium tuberculosis was behind the scourge. It was the first time that a particular microbe was linked to a disease.

More than a century later, aspects of the ailment now most commonly called TB remain unexplained. Some people infected by the microbe soon show symptoms such as fever, wasting, and cough, but others don't. Unlike many bacteria, M. tuberculosis can linger in a body for decades after the initial infection without producing symptoms.

It can surge into action at any time, sometimes with deadly force. About 10 percent of people with l