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Tuberculosis: Causes, Symptoms, Diagnosis & Treatment: Fast Facts

Tuberculosis: Causes, Symptoms, Diagnosis & Treatment: Fast Facts

  • June 4, 2024
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Tuberculosis Pathophysiology

Tuberculosis (TB) is a complex infectious disease caused by the bacterium Mycobacterium tuberculosis. The pathophysiology of TB involves a series of intricate interactions between the pathogen and the host’s immune system. This article provides a detailed examination of the mechanisms underlying the development, progression, and pathology of tuberculosis.

Entry and Initial Infection

TB is primarily transmitted through airborne droplets. When an individual with active pulmonary TB coughs or sneezes, droplets containing M. tuberculosis are expelled into the air and can be inhaled by another person. Upon inhalation, the bacteria reach the alveoli of the lungs, where the infection process begins .

Primary Infection and Immune Response

In the alveoli, M. tuberculosis is phagocytosed by alveolar macrophages. However, the bacteria possess several mechanisms to evade destruction:

  • Inhibition of Phagosome-Lysosome Fusion: M. tuberculosis can prevent the fusion of phagosomes containing the bacteria with lysosomes, thereby avoiding degradation by lysosomal enzymes .
  • Survival in Macrophages: The bacteria can persist and replicate within macrophages, which serve as a protected niche .

The initial immune response involves the recruitment of more immune cells to the site of infection. Infected macrophages release cytokines and chemokines that attract other immune cells, including neutrophils, monocytes, and lymphocytes. This leads to the formation of a granuloma, a hallmark of TB infection.

Granuloma Formation

Granulomas are organized structures formed to contain the infection. They consist of infected macrophages surrounded by a ring of lymphocytes and other immune cells. The center of the granuloma may undergo necrosis, forming a caseous (cheese-like) necrotic core. Granulomas serve two main purposes:

  • Containment of Bacteria: They physically contain the bacteria, preventing their spread.
  • Localized Immune Response: They create a microenvironment for a sustained immune response .

Latent TB Infection

In most healthy individuals, the immune system successfully contains the bacteria within granulomas, leading to a latent TB infection. In this state, the bacteria are alive but dormant and the individual is asymptomatic and not contagious. However, latent TB can reactivate if the immune system becomes compromised, leading to active TB disease .

Active TB Disease

If the immune system fails to contain the infection, or if the latent bacteria reactivate, active TB disease develops. The bacteria proliferate, causing extensive tissue damage. In the lungs, this results in cavitation, where large cavities form due to the destruction of lung tissue. Active TB is characterized by the following:

  • Persistent Cough: Often producing sputum, which may be bloody.
  • Fever and Night Sweats: Due to the systemic inflammatory response.
  • Weight Loss and Fatigue: Resulting from chronic inflammation and catabolic processes .

Extrapulmonary TB

While TB primarily affects the lungs, it can spread to other parts of the body through the bloodstream or lymphatic system, leading to extrapulmonary TB. Common sites include:

  • Lymph Nodes: Leading to lymphadenitis.
  • Pleura: Causing pleuritis or pleural effusion.
  • Bones and Joints: Resulting in osteomyelitis or arthritis.
  • Central Nervous System: Leading to meningitis.
  • Genitourinary System: Affecting the kidneys and reproductive organs .

Immune Evasion and Persistence

M. tuberculosis has evolved several strategies to evade the host immune system and persist within the host:

  • Cell Wall Components: The lipid-rich cell wall of M. tuberculosis provides resistance to desiccation and chemical damage.
  • Secretion Systems: The bacteria use specialized secretion systems to manipulate host cell processes and inhibit immune responses .

Tuberculosis (TB) remains a significant global health concern, affecting millions of people worldwide. Despite advances in medical science, TB continues to challenge public health systems, particularly in developing countries. This article delves into the causes, symptoms, diagnosis, and treatment of tuberculosis, providing a comprehensive overview of this persistent disease.

Causes of Tuberculosis

Tuberculosis is caused by the bacterium Mycobacterium tuberculosis. The bacteria primarily attack the lungs, but they can also affect other parts of the body, including the kidneys, spine, and brain. TB spreads through the air when a person with active TB of the lungs or throat coughs, speaks, or sneezes, releasing tiny droplets that contain the bacteria .

Certain factors increase the risk of developing TB, including:

  • Close Contact: Spending time with someone who has active TB.
  • Weakened Immune System: Conditions like HIV/AIDS, diabetes, or certain medications that suppress the immune system.
  • Travel or Living in Areas with High TB Prevalence: Especially parts of Africa, Asia, and Latin America.
  • Substance Abuse: Prolonged alcohol or drug use can weaken the immune system.
  • Living Conditions: Crowded or unsanitary living conditions facilitate the spread of TB .

Symptoms of Tuberculosis

TB infection can be latent or active. Latent TB means the bacteria are in the body but inactive, causing no symptoms and not contagious. However, it can turn into active TB.

Active TB symptoms can vary depending on the organs involved, but common symptoms include:

  • Persistent Cough: Lasting more than three weeks, sometimes with blood in the sputum.
  • Chest Pain: Pain during breathing or coughing.
  • Fatigue: Persistent feeling of tiredness.
  • Fever and Chills: Often with night sweats.
  • Weight Loss: Unintentional loss of weight.
  • Loss of Appetite .

Diagnosis of Tuberculosis

Diagnosing TB involves several methods:

  • Tuberculin Skin Test (TST): Also known as the Mantoux test, where a small amount of tuberculin is injected under the skin. A positive reaction often indicates TB infection, but further tests are needed to confirm if it’s active TB.
  • Blood Tests: Interferon-Gamma Release Assays (IGRAs) measure the immune response to TB bacteria.
  • Imaging Tests: Chest X-rays can reveal changes in the lungs indicative of TB.
  • Sputum Tests: Microscopic examination and culture of sputum samples can detect TB bacteria. Molecular tests like the GeneXpert MTB/RIF test also identify TB and its resistance to rifampicin, a key TB drug .

Treatment of Tuberculosis

Treatment of TB requires a long-term course of antibiotics. The standard regimen for active TB involves:

  • First-line Antibiotics: Usually a combination of isoniazid, rifampicin, ethambutol, and pyrazinamide for two months, followed by isoniazid and rifampicin for another four months.
  • Directly Observed Therapy (DOT): Ensures patients adhere to their medication regimen by having healthcare workers observe and record each dose taken.

Treatment for latent TB typically involves a shorter course of fewer antibiotics to prevent the development of active TB .

Challenges and Future Directions

Drug-Resistant TB: One of the major challenges is multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB), which require longer, more complex treatment with second-line drugs.

Vaccine Development: The BCG vaccine offers limited protection and is not very effective in adults. Research is ongoing to develop more effective vaccines.

Public Health Initiatives: Continued efforts in improving diagnostic methods, treatment regimens, and prevention strategies are crucial. Education and awareness programs play a significant role in reducing the spread of TB .

References

  1. Centers for Disease Control and Prevention (CDC). (2021). Tuberculosis (TB): Transmission and Risk Factors. Retrieved from https://www.cdc.gov/tb/topic/basics/transmission.htm
  2. World Health Organization (WHO). (2020). Tuberculosis. Retrieved from https://www.who.int/news-room/fact-sheets/detail/tuberculosis
  3. Mayo Clinic. (2021). Tuberculosis: Risk Factors. Retrieved from https://www.mayoclinic.org/diseases-conditions/tuberculosis/symptoms-causes/syc-20351250
  4. National Institute of Allergy and Infectious Diseases (NIAID). (2020). Tuberculosis. Retrieved from https://www.niaid.nih.gov/diseases-conditions/tuberculosis
  5. MedlinePlus. (2021). Tuberculosis Symptoms. Retrieved from https://medlineplus.gov/tuberculosis.html
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  11. Tuberculosis Research Centre. (2020). Challenges in TB Treatment. Retrieved from https://www.trc-chennai.org/challenges-tb-treatment
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  22. Kumar, V., Abbas, A. K., & Aster, J. C. (2020). Robbins and Cotran Pathologic Basis of Disease (10th ed.). Elsevier.

By understanding the causes, symptoms, diagnosis, and treatment of tuberculosis, we can better combat this disease and move closer to a TB-free world.

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