Pathophysiology of TB
Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis. The pathophysiology of TB involves several steps:
1. Transmission: TB is primarily transmitted through the air when an infected individual coughs, sneezes, or talks, and releases respiratory droplets containing the bacteria. When a person inhales these droplets, the bacteria can reach the lungs and establish an infection.
2. Inhalation and deposition: Once inhaled, the M. tuberculosis bacteria enter the airways and are deposited primarily in the alveoli, the tiny air sacs within the lungs. The bacteria are then taken up by alveolar macrophages, which are the immune cells responsible for engulfing and destroying invading pathogens.
3. Initial immune response: Upon infection, the body's immune response is initiated. Alveolar macrophages release various inflammatory molecules, such as cytokines, to attract other immune cells to the site of infection.
4. Granuloma formation: Granulomas are organized collections of immune cells that form in response to the infection. These structures help contain the bacteria and prevent its spread. Within the granuloma, macrophages surround and try to kill the bacteria by releasing toxic molecules, such as reactive oxygen species and nitric oxide.
5. Latent infection: In some cases, the immune system is able to control the infection, resulting in a latent TB infection. Latent TB is characterized by the presence of M. tuberculosis bacteria within granulomas, but without active disease. People with latent infection do not have symptoms and are not infectious, but they are at risk of developing active TB in the future.
6. Active infection: If the immune system is unable to control the initial infection, the bacteria can multiply and spread within the lungs, leading to active TB disease. The bacteria can also spread to other parts of the body, such as the lymph nodes, bones, and central nervous system.
7. Tuberculous pneumonia: In active TB disease, the bacteria can cause inflammation and damage to lung tissue, leading to the development of tuberculous pneumonia. This can result in symptoms such as cough, sputum production, chest pain, and shortness of breath.
8. Disseminated TB: In severe cases, the bacteria can spread through the bloodstream to other organs, causing disseminated or miliary TB. This can affect multiple organs, including the brain, kidneys, liver, and bones, and can be life-threatening if left untreated.
Overall, the pathophysiology of TB involves a dynamic interplay between the bacteria and the host immune response. The ability of the immune system to control the infection determines whether an individual develops latent infection or progresses to active disease.