Tuberculosis (TB) is a contagious infectious disease. It can have either active or inactive forms. Although it can affect many organ systems, it mostly affects the lungs.

TB is caused by the bacterium Mycobacterium tuberculosis. When a person with active TB of the lungs coughs or sneezes, people nearby may inhale the bacteria. TB is easily spread in crowded conditions, though it may take several hours of continuous exposure to transmit infection. Brief or casual contact with someone who has TB will usually not lead to infection. TB is most likely to become active when spread among people who are ill or have weakened immune systems.

Pathway to the Lungs
Air pathway breathing
Mycobacterium tuberculosis is inhaled through the mouth and nose and travels down into the lungs causing TB.
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