Tuberculosis (TB) is a contagious infectious disease caused primarily by the bacterium Mycobacterium tuberculosis. It most commonly affects the lungs (pulmonary TB), but it can involve nearly any organ system, including the lymph nodes, bones, kidneys, and central nervous system. Transmission occurs through airborne droplets when an infected individual coughs, speaks, or sneezes.
Despite being preventable and treatable, tuberculosis remains one of the leading infectious causes of death worldwide. Its persistence reflects a combination of biological resilience, social determinants of health, and challenges in diagnosis and treatment adherence.
🧬 Causative Agent and Pathophysiology
The pathogen, Mycobacterium tuberculosis, is a slow-growing, rod-shaped bacterium characterized by a waxy cell wall rich in mycolic acids. This structure makes it resistant to many disinfectants and allows it to survive within host immune cells.
After inhalation, bacteria reach the alveoli of the lungs, where they are engulfed by macrophages. Instead of being destroyed, the organisms can persist inside these immune cells. The body responds by forming granulomas—organized clusters of immune cells that attempt to contain the infection.
Two major states may result:
- Latent TB infection (LTBI): Bacteria remain dormant without symptoms; individuals are not contagious.
- Active TB disease: Bacteria multiply, causing symptoms and enabling transmission.
Approximately one-quarter of the global population is estimated to carry latent TB, though only a fraction develop active disease.
🫁 Clinical Manifestations
Pulmonary TB
The most common form presents with:
- Persistent cough (often lasting more than three weeks)
- Hemoptysis (coughing up blood)
- Chest pain
- Fever and night sweats
- Unintentional weight loss
Extrapulmonary TB
TB may affect:
- Lymph nodes (scrofula)
- Spine (Pott’s disease)
- Meninges (tuberculous meningitis)
- Kidneys and genitourinary system
Symptoms vary according to the organ involved.
🔬 Diagnosis
Diagnosis involves a combination of clinical evaluation and laboratory testing:
- Sputum smear microscopy using Ziehl–Neelsen staining
- Culture methods, the diagnostic gold standard
- Molecular tests (e.g., nucleic acid amplification tests)
- Chest radiography
Latent infection is detected using the tuberculin skin test (TST) or interferon-gamma release assays (IGRAs).
💊 Treatment
Tuberculosis is treatable with a multi-drug antibiotic regimen. Standard first-line therapy typically includes:
- Isoniazid
- Rifampin
- Pyrazinamide
- Ethambutol
Treatment generally lasts six months or longer. Strict adherence is essential to prevent relapse and the emergence of drug-resistant strains.
Drug-Resistant TB
Multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) arise when bacteria evolve resistance to standard medications. These forms require longer, more complex treatment regimens and present major public health challenges.
🌍 Epidemiology
TB disproportionately affects low- and middle-income countries. Risk factors include:
- HIV infection
- Malnutrition
- Overcrowding
- Limited access to healthcare
Co-infection with HIV significantly increases the risk of progression from latent to active disease due to immune suppression.
💉 Prevention
Vaccination
The Bacille Calmette-Guérin (BCG) vaccine provides partial protection, particularly against severe forms in children. However, its efficacy against adult pulmonary TB is variable.
Public Health Measures
- Early detection and treatment
- Contact tracing
- Improved ventilation in high-risk settings
- Preventive therapy for high-risk individuals
TB control requires sustained global coordination due to its airborne transmission and long latency.
🧠 Biological and Social Significance
Tuberculosis illustrates the interplay between pathogen biology and social structure. Its slow progression, latency, and airborne transmission make it uniquely persistent. It is both a biomedical challenge and a reflection of inequities in global health infrastructure.
From a microbiological perspective, M. tuberculosis demonstrates sophisticated immune evasion strategies. From a public health standpoint, TB underscores the importance of surveillance, antibiotic stewardship, and vaccination research.
📚 See Also
- Mycobacterium tuberculosis
- Antibiotic resistance
- Bacille Calmette-Guérin vaccine
- HIV/AIDS
- Infectious disease epidemiology
Last Updated on 2 weeks ago by pinc