Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis. It spreads through the air when an infected person coughs, sneezes, or speaks, releasing tiny droplet nuclei. TB remains a leading infectious cause of death worldwide, despite being both preventable and curable. The infection can lie dormant for years in a state known as latent TB. Active disease occurs when the immune system fails to contain the multiplying bacteria.
Effects on the Respiratory System
Active tuberculosis most commonly targets the lungs, known as pulmonary TB, which makes the disease contagious. The bacteria proliferate within the lung tissue, causing an inflammatory response that forms characteristic lesions called granulomas. As the disease advances, it destroys the functional air sacs and surrounding tissue, leading to a breakdown of the lung structure.
Tissue damage physically manifests as a persistent, chronic cough lasting three weeks or longer. This cough may produce sputum, sometimes streaked with blood (hemoptysis), indicating damage to pulmonary blood vessels. Patients frequently experience chest pain or discomfort, especially when breathing deeply, due to inflammation of the lung lining or the formation of cavities.
Systemic symptoms accompany the localized respiratory distress as the body responds to the bacterial infection. Common indicators of active disease include a low-grade fever, unexplained weight loss, and loss of appetite. Drenching night sweats, persistent fatigue, and chills contribute to a general feeling of malaise. Without effective treatment, progressive destruction of lung architecture can lead to acute respiratory distress and respiratory failure.
Effects Beyond the Lungs
While the lungs are the primary site of infection, Mycobacterium tuberculosis can spread via the bloodstream or lymphatic system to virtually any other organ, resulting in extrapulmonary TB (EPTB). EPTB is generally not contagious, but its effects are diverse and depend on the site of infection. The lymphatic system is a frequent target, causing tubercular lymphadenitis, which manifests as enlarged, painless, firm lymph nodes, most commonly in the neck (scrofula).
Infections of the skeletal system, known as Pott’s disease or spinal TB, are destructive, attacking the vertebrae and intervertebral discs. This erosion leads to severe back pain, spinal deformity, and potential neurological complications if the infection compresses the spinal cord. When the bacteria reach the central nervous system, they cause tuberculous meningitis, an inflammation of the membranes surrounding the brain and spinal cord. This neurological involvement is severe, often causing headaches, confusion, and life-threatening complications.
The bacteria can also affect the genitourinary system, primarily the kidneys and bladder. Infection here causes flank pain, blood in the urine, and frequent, painful urination. Over time, this chronic infection causes scarring and obstruction, potentially leading to irreversible kidney damage and chronic renal failure. In rare cases, a disseminated infection known as miliary TB occurs, involving multiple organs like the liver, spleen, and adrenal glands, leading to widespread organ dysfunction.
Long-Term Health Consequences
Even after successfully completing the multi-drug treatment regimen for active TB, patients experience lasting health impairments, known as sequelae. The damage from the acute infection often results in permanent alterations to the lungs’ structure, termed post-TB lung disease (PTLD). Up to 50% of survivors may be left with chronic pulmonary dysfunction, severely impacting their quality of life.
This residual damage includes extensive lung scarring and fibrosis, which permanently restrict lung capacity and impair oxygen exchange. These chronic structural changes can accelerate the development of conditions like Chronic Obstructive Pulmonary Disease (COPD) or bronchiectasis. This leads to persistent symptoms such as shortness of breath and a chronic cough, significantly affecting a survivor’s ability to work and participate in daily life.
Extrapulmonary infections also cause chronic organ dysfunction long after the bacteria are cleared. For example, prior urogenital TB can result in chronic kidney disease, while adrenal gland involvement may lead to adrenal insufficiency (Addison’s disease). Treated TB patients face a higher long-term risk of all-cause mortality compared to the general population, suggesting a reduced life expectancy. Physical disability combined with psychological distress, such as anxiety and depression, underscores the chronic burden of surviving the disease.