Tuberculosis - causes, symptoms, diagnosis, treatment, pathology

Tuberculosis (TB), caused by mycobacterium tuberculosis, infects approximately two billion people globally. Despite this staggering number, 90-95% of infected individuals remain asymptomatic due to the immune system's ability to contain the bacteria in a latent state. This dormant phase prevents symptoms and transmission but can reactivate if the immune system weakens due to factors like aging or illnesses such as AIDS.

Mycobacteria are strict aerobes, requiring oxygen to survive. They possess a distinctive waxy cell wall due to mycolic acid production, making them "acid-fast" and resistant to alcohol-based decolorization during staining processes like Ziehl–Neelsen stain. This unique structure not only gives them their bright red color in stains but also makes them highly resilient against weak disinfectants.

Mycobacterium tuberculosis is primarily transmitted through inhalation, reaching the lungs. While most bacteria are trapped and cleared by mucus in upper airways, TB bypasses these defenses to reach deep alveoli where macrophages attempt to destroy it. Normally, macrophages engulf foreign cells into a phagosome that fuses with lysosomes containing enzymes for breakdown. However, TB produces a protein preventing this fusion inside the macrophage, enabling its survival.

Tuberculosis begins with the bacteria proliferating, causing a localized infection known as primary tuberculosis. Most individuals remain asymptomatic or experience mild flu-like symptoms initially. After about three weeks, cell-mediated immunity activates, forming granulomas to contain the bacteria; this process leads to caseous necrosis within these structures called Ghon foci. The infection may spread to hilar lymph nodes creating a characteristic "Ghon complex," which can calcify into visible scar tissue on x-rays (Ranke complex). While some infections resolve completely, others leave dormant mycobacteria that can reactivate under immune-compromised conditions.

Miliary tuberculosis can spread beyond the lungs, affecting various organs and causing severe complications. When it reaches the kidneys, it leads to sterile pyuria with elevated white blood cells in urine. Invasion into brain meninges results in meningitis; lumbar vertebrae involvement causes Pott disease; adrenal gland infection triggers Addison’s disease; and liver damage manifests as hepatitis.

Tuberculosis (TB) testing begins with the purified protein derivative (PPD) skin test, where tuberculin is injected into the dermis. A positive reaction indicates prior exposure to TB but does not distinguish between active and latent infections. Alternatively, interferon gamma release assays (IGRAs), a blood test more specific to TB proteins, avoid false positives from BCG vaccination and do not require follow-up visits like PPD tests. For individuals with positive results or symptoms such as fever, night sweats, weight loss, or hemoptysis (coughing up blood), further diagnostics include chest X-rays and sample collection via sputum analysis or bronchoalveolar lavage. These samples undergo lab procedures including staining, culture growths, and PCR testing to confirm evidence of active disease.

Latent TB infection is treated with a single drug, commonly Isoniazid, over nine months. Active TB disease requires combinations of antibiotics like isoniazid, rifampin, ethambutol, and pyrazinamide to render patients non-infectious within weeks. During the infectious period—primarily in adults with reactivated TB—patients are isolated in negative pressure rooms while visitors wear N-95 masks for protection against aerosols. Even after becoming non-contagious, prolonged multi-drug therapy continues under directly observed therapy (DOT) to ensure complete bacterial eradication.

The emergence of drug-resistant tuberculosis (TB) strains, such as MDR-TB and XDR-TB, poses a significant global health challenge due to their resistance to standard antibiotics. Effective treatment requires tailored medications targeting specific TB strains, using multiple drugs simultaneously to prevent further resistance and ensuring the full course is completed for eradication. A breakthrough therapy combining pretomanid with bedaquiline and linezolid has shown nearly 90% effectiveness against XDR-TB in recent studies. This oral combination offers an accessible solution while maintaining high efficacy.

Understanding Tuberculosis and Its Progression Tuberculosis (TB) is an infection caused by Mycobacterium tuberculosis, primarily affecting the lungs. The immune system forms granulomas to contain the infection, leading to caseous necrosis in areas like Ghon focus and nearby lymph nodes—together forming a Ghon complex. If immunity weakens due to factors like AIDS or aging, TB can reactivate, spreading within the lungs as cavities or disseminating through blood vessels causing systemic miliary TB.

Diagnosis and Treatment of Active Tuberculosis Diagnosing TB involves PPD skin tests or IGRA blood tests alongside chest X-rays for active disease signs. Symptoms such as fever, night sweats, weight loss, and hemoptysis prompt sputum analysis via staining or PCR for bacterial identification. Treatment requires prolonged antibiotic regimens tailored specifically for drug-resistant strains like MDR-TB and XDR-TB.