Tuberculosis (TB) is an infectious or contagious disease. It is caused due to bacteria known as Mycobacterium tuberculosis that spread from person to person through airborne particles i.e. when people infected with the bacilli cough, sneeze, talk or spit, they propel TB germs known as TB bacilli into the air. When the bacilli are inhaled by a healthy person, he or she gets infected. Inhaling a small number of the bacilli can cause infection.
Everyone, who gets infected with TB bacilli, will not become sick. Some people have a strong immune system that fights the TB bacilli and kills it. In others, the immune system “walls off" the germ where it can lie dormant (inactive) for years. These people have latent TB infection i.e., they carry the bacteria, but do not have any symptoms. If the immune system fails to kill or contain the germ, infection with TB bacilli leads to an active disease. In these people, the TB bacilli multiply and cause damage in the body and therefore, cause them to become sick and contagious (transmit the disease).
TB is a major cause of death in the developing countries, especially, in Africa and Asia. According to studies, at least one person in the world is newly infected with TB bacilli every second and about 5% to 10% of people infected with TB become actively sick. According to current estimates, about one third of the world's population is currently infected with TB.
In a person infected with TB, the bacilli grow and multiply in the lung. It causes pneumonia and symptoms such as chest pain, coughing up blood and a prolonged cough. In some cases, the infection may spread to the lymph nodes near the heart and lungs, which become enlarged. Some people with the infection do not develop disease in the lungs. The TB germ may spread to other parts of the body and damage the kidneys, bones and brain (meninges that line the spinal cord and brain).
TB can be cured in most people with treatment. Treatment of TB, however, is for a prolonged duration (may be months or years). The risk of TB increases in people with a weak immune system such as HIV/AIDS. They tend to have much severe form of the disease, which may be difficult to treat.
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