Tuberculosis spreads through the air when a person with untreated pulmonary TB coughs or sneezes. Once in the body, the tuberculosis bacilli has about 5 stages in its life cycle: Stage 1: Onset Bacteria is inhaled through the air and typically engulfed by alveolar macrophages. At this instant, disease progression depends on the virulence of the inhaled strain and the anti mycobacterial capabilities of the macrophage in question. In some cases, the bacteria are able to reproduce and initiate the infection. Tuberculosis begins when the inhaled mycobacterial nuclei reach aveolar machrophages Stage 2: Symbiosis If the initial macrophage does not succeed in killing the bacteria, the bacteria will replicate until the macrophage bursts. The bacteria are now engulfed by other alveolar macrophages and non activated macrophages. The macrophages that arrive from the bloodstream engulf the exposed bacteria in a symbiotic manner—neither the host nor the bacteria is harmed
8. Contd Stage 3: Initial Caseous Necrosis The next stage of disease development begins when bacterial reproduction slows. Growth slows because as the bacteria reproduce, they kill all the surrounding non activated macrophages and run out of cells to divide within. In addition, the increased number of bacteria produces anoxic conditions and reduces the local pH The bacteria can no longer reproduce in this tubercule, but can remain alive for long periods of time at this state. The host kills its own tissues to prevent the spread of the bacteria. Also at this stage, the host will test positive for tuberculin. Stage 4: Interplay of Tissue-Damaging and Macrophage Activating Immune Response Macrohpages surround the tubercule, some of which may be inactivate. M. tuberculosis uses the inactive macrophages to reproduce, causing the tubercule to grow. The tubercule may break off or spread into the bronchus, and then other parts of the lung. If the tubercules reach the blood stream, the patient can develop tuberculosis outside of the lungs, which is known as milliary tuberculosis. Secondary lesion can develop almost anywhere within the body, but are commonly found in the bones, joints, lymph nodes, and genitourinary system. Stage 5: Liquefaction and Cavity Formation At some point the centres of the tubercles may liquefy, which produces a very conducive environment for the bacteria and rapid spread of the disease. Only a very small % of infected individuals will progress to this stage