The story

Many people think of tuberculosis as being a disease from the past. The truth is far from it: Tuberculosis is mutating into dangerous new strains for which there is no known cure.

One of the most frightening strains is XDR-TB, which stands for extensively drug-resistant TB.

Unlike less virulent strains, XDR-TB does not respond to the antibiotics that are usually used to treat TB. The disease is virtually incurable and threatens to become a pandemic.

About 40,000 new cases of XDR-TB emerge every year, the World Health Organization estimates.

Award-winning photojournalist James Nachtwey, who has chronicled the death and devastation the disease is bringing to many countries around the world, describes XDR-TB as "a merciless, man-eating predator lurking in the shadows." Read full article »

Vital Signs
Each month CNN's Dr. Sanjay Gupta brings viewers health stories from around the world.

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