TB is caused by Mycobacterium tuberculosis, a small, aerobic, non-motile bacillus. TB is widespread, deadly and causes the highest number of deaths worldwide. One third of the global population has latent TB infection. Bacteria usually attack lungs. But, TB bacteria can attack any part of the body such as the spine, brain and kidney. Symptoms for TB infection vary according to the organs involved, tuberculosis in kidneys causes blood in urine while, tuberculosis of spine may cause back pain.
Latent TB: This condition of TB infection, in which the bacteria remain in an inactive state and cause no symptoms. It is also called inactive TB or TB infection, isn't contagious, but can turn into active TB, so treatment is mandatory for the person with latent TB and to help limit the spread of TB.
Active TB: Active TB is highly contagious and can spread to others. It may occur in the first few weeks after infection with the bacteria or it might occur years later.
The M. tuberculosis complex includes four other TB-causing mycobacterial species:
• M. bovis: It was once a common cause of tuberculosis, but the awakening of pasteurized milk has almost completely eradicated as a public health issue in developed countries.
• M. africanum: It is not widespread, but it is a significant cause of tuberculosis in parts of A africa.
• M. canetti: It is rare and seems to be limited to the Horn of Africa, although a couple of cases have been seen in African emigrants.
• M. microti. It is also rare and is seen only in immunodeficient people, although its utility may be significantly underestimated.
• M. pinnipedii: is also called as the seal bacillus for causing TB in fish-eating sea animal and on very rare occasions these pathogens were found to cause TB in humans.
Other known pathogenic mycobacteria include M. leprae, M. kansasii., M. avium. and M. pinnipedii. The latter two species are classified as "Non-tuberculous Mycobacteria". NTM neither causes leprosy nor TB, but cause a pulmonary disease that resembles TB.