Pathophysiology of Pulmonary Tuberculosis
Introduction
Tuberculosis (TB) is a chronic infectious disease caused by the bacterium Mycobacterium tuberculosis. It primarily affects the lungs, but it can also spread to other parts of the body. The disease is spread through the air when a person with active TB coughs, sneezes, or speaks.
Pathophysiology
The pathogenesis of TB is complex and involves a complex interplay between the host immune system and the bacterium.
1. Infection:
- Inhaled Mycobacterium tuberculosis: The bacteria are inhaled into the lungs, usually as small droplets of saliva or mucus.
- Initial infection: The bacteria are engulfed by macrophages, immune cells that normally fight infection.
- Intracellular survival: Mycobacterium tuberculosis is resistant to macrophage killing mechanisms, allowing it to survive and even multiply within these cells.
2. Immune Response:
- Cell-mediated immunity: The body mounts a cell-mediated immune response, involving CD4+ T lymphocytes (helper T cells) and CD8+ T lymphocytes (cytotoxic T cells).
- Granuloma formation: These immune cells form a granuloma, a localized inflammatory response, around the infected macrophages. Granulomas are the hallmark of TB infection.
- Caseous necrosis: In the center of the granuloma, an area of caseous necrosis (cheese-like material) develops, consisting of dead cells and bacteria.
3. Latent TB:
- In most cases: The immune response is successful in containing the infection.
- Latent TB: The bacteria remain dormant within the granulomas, and the person does not experience any symptoms.
4. Active TB:
- Reactivation: The bacteria can reactivate if the immune system weakens due to factors such as HIV infection, malnutrition, or certain medications.
- Symptoms of active TB: Symptoms include cough, fever, weight loss, night sweats, and chest pain.
- Cavitation: If active TB progresses, the granulomas can rupture and form cavities in the lungs, allowing bacteria to spread to other parts of the body.
Transmission
- Airborne droplets: The bacteria are spread through the air when a person with active TB coughs, sneezes, or speaks.
- Close contact: People who are in close contact with someone with active TB are at increased risk of infection.
- Susceptibility: People with weakened immune systems are more susceptible to TB infection.
Treatment
- Antibiotics: Anti-TB medications are used to kill the bacteria and prevent the disease from progressing.
- Duration: Treatment for active TB typically lasts for six to nine months.
- Multidrug therapy: Multiple medications are used to reduce the risk of drug resistance.
Prevention
- Vaccination: The BCG vaccine is available to protect against TB, but its effectiveness varies.
- Avoiding contact: People with active TB should avoid close contact with others to prevent spreading the infection.
- Early diagnosis and treatment: Early diagnosis and treatment of active TB can prevent the disease from spreading and prevent serious complications.
