Tuberculosis (TB) is an infectious air-borne disease caused primarily by rod-shaped bacteria called Mycobacterium tuberculosis. Additionally, there are four very closely related mycobacterial species (M. bovis, M. africanum, M. microti, and M. canetti) that together they comprise what is known as the M. tuberculosis complex---this can also cause tuberculosis disease. The bacteria can attack any part of your body, including the kidneys, spine, or even the brain, but they usually attack the lungs. If not treated properly, TB disease can be fatal.
Tuberculosis has two general states: latent TB infection and active TB disease. Only those who develop active TB can transmit the disease.