Mycobacterium tuberculosis (MTB) causes tuberculosis (TB) when inhaled bacteria reach the alveoli in the lungs and initiate an infection.
Here's a more detailed breakdown:
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Transmission: TB is primarily spread through the air when a person with active pulmonary TB coughs, sneezes, speaks, or sings. This releases microscopic droplets containing MTB.
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Inhalation: If another person inhales these droplets, the MTB bacteria can reach the small air sacs in the lungs called alveoli.
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Initial Infection: Once in the alveoli, MTB is ingested by alveolar macrophages, which are immune cells that normally engulf and destroy foreign particles. However, MTB has mechanisms to survive and even replicate within these macrophages.
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Immune Response: The body mounts an immune response, recruiting other immune cells to the site of infection. This leads to the formation of granulomas, which are collections of immune cells that attempt to wall off the infection.
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Latent TB Infection (LTBI): In many cases, the immune system is able to control the infection, preventing it from spreading and causing active disease. This results in latent TB infection (LTBI). People with LTBI have TB bacteria in their body, but they don't have symptoms and are not contagious. The bacteria are essentially dormant within the granulomas.
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Active TB Disease: If the immune system is weakened (e.g., due to HIV infection, malnutrition, diabetes, or certain medications), MTB can escape from the granulomas and multiply, leading to active TB disease. Active TB disease typically affects the lungs (pulmonary TB) but can also spread to other parts of the body (extrapulmonary TB).
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Damage and Symptoms: The active multiplication of MTB and the resulting inflammatory response cause tissue damage in the lungs and other organs. This damage leads to the symptoms of TB, such as coughing, fever, weight loss, and night sweats.
In summary, MTB causes TB by establishing an infection in the lungs following inhalation, subverting the immune system, and potentially progressing from a latent state to active disease characterized by bacterial replication and tissue damage.
