Tuberculosis (TB)

Overview

Tuberculosis (TB) is a contagious bacterial infection that primarily affects the lungs, though it can also impact other parts of the body, including the kidneys, spine, and brain. The disease is caused by the bacterium Mycobacterium tuberculosis and spreads through the air when an infected person coughs, sneezes, or talks, releasing infectious droplets into the environment. While TB is preventable and treatable, it remains one of the leading causes of death worldwide, particularly in low- and middle-income countries.

There are two primary forms of TB:

1. Latent Tuberculosis: In this stage, the person has been infected with Mycobacterium tuberculosis, but the bacteria are inactive in the body. Individuals with latent TB do not show symptoms, are not contagious, and may never develop active disease unless their immune system becomes weakened later in life.
2. Active Tuberculosis: This occurs when the bacteria multiply, and the individual begins to show symptoms of the disease. Active TB is contagious and can be transmitted to others through the air.

Pathophysiology

The bacterium Mycobacterium tuberculosis enters the body through the respiratory system and usually infects the lungs. However, the infection can spread to other organs if not contained. Once inside the lungs, the bacteria are engulfed by the body’s immune cells, but they can survive and replicate within these cells, leading to an immune response. Infected individuals may experience inflammation and granuloma formation, which is the body’s attempt to contain the infection. This localized immune response can cause lung damage, which leads to the symptoms of active tuberculosis.

Risk Factors

While TB can affect anyone, several factors increase the risk of contracting the disease:

• Close Contact with Infected Individuals: TB is most often transmitted in crowded or poorly ventilated environments. Household contacts and individuals in healthcare settings are at a higher risk.
• Weakened Immune System: Conditions such as HIV/AIDS, diabetes, and cancer, or medications that suppress the immune system (e.g., chemotherapy, steroids) increase the likelihood of developing active TB.
• Malnutrition: Inadequate nutrition can impair the immune system and increase the susceptibility to infections like TB.
• Age: Very young children and the elderly have weaker immune systems, which increases the risk of contracting TB.
• Drug and Alcohol Use: These substances weaken the immune system and promote risky behaviors, such as close contact with individuals carrying the infection.

Symptoms

The symptoms of active tuberculosis can vary depending on the part of the body affected, but common symptoms include:

• Chronic Cough: A persistent cough lasting more than three weeks is one of the most common symptoms of TB.
• Coughing Up Blood: Hemoptysis, or coughing up blood, is a concerning symptom that may indicate advanced TB.
• Night Sweats: Individuals with TB often experience excessive sweating, particularly at night.
• Fatigue and Weakness: TB can cause a general feeling of tiredness and lack of energy.
• Weight Loss: Unexplained weight loss and loss of appetite are common in individuals with TB.
• Fever: Low-grade fever, especially in the evening, is a hallmark sign of active TB.
• Chest Pain: Pain in the chest may occur due to inflammation and damage to the lungs.
• Shortness of Breath: In more severe cases, the infection may lead to difficulty breathing due to lung damage.

Diagnosis

Diagnosing tuberculosis requires a combination of clinical evaluation, laboratory tests, and imaging studies. Key diagnostic methods include:

• Tuberculin Skin Test (TST): Also known as the Mantoux test, this involves injecting a small amount of purified protein derivative (PPD) under the skin and measuring the reaction 48-72 hours later. A positive result indicates prior exposure to the TB bacteria, though it does not distinguish between latent and active disease.
• Chest X-ray: A chest X-ray is used to look for signs of lung damage caused by TB. It can reveal the presence of lesions, nodules, or cavities in the lungs.
• Sputum Smear Microscopy: This test examines sputum (mucus from the lungs) under a microscope to detect the presence of Mycobacterium tuberculosis. It is a quick and inexpensive way to confirm the diagnosis of active TB.
• Sputum Culture: Culturing sputum samples in a laboratory can take several weeks but is the most reliable way to diagnose TB and identify drug-resistant strains.
• GeneXpert MTB/RIF Test: A rapid molecular test that can detect TB DNA in sputum and also identify resistance to rifampicin, one of the primary drugs used to treat TB.
• CT Scan: In some cases, a high-resolution computed tomography (CT) scan may be used to get a more detailed image of the lungs and surrounding structures.

Treatment

The treatment for tuberculosis involves a combination of antibiotics. It is crucial for individuals with TB to complete the full course of treatment, which typically lasts for 6 to 9 months to prevent the development of drug resistance. The most commonly used drugs for treating TB are:

• Isoniazid
• Rifampicin
• Pyrazinamide
• Ethambutol

For multi-drug-resistant tuberculosis (MDR-TB), which does not respond to the first-line medications, second-line drugs such as fluoroquinolones and injectable agents may be required. Treatment for MDR-TB can take up to 18-24 months and requires close monitoring to ensure adherence and manage potential side effects.

Drug-Resistant Tuberculosis

Drug-resistant TB has become a significant challenge in global TB control. Resistance can develop due to incomplete or inappropriate treatment, as well as inadequate healthcare infrastructure. The most common forms of drug-resistant TB are:

• Multi-Drug Resistant TB (MDR-TB): TB that is resistant to at least isoniazid and rifampicin, the two most powerful first-line anti-TB drugs.
• Extensively Drug-Resistant TB (XDR-TB): A more severe form of MDR-TB that is resistant to second-line drugs as well, leaving limited treatment options.

Prevention

Preventing the spread of TB is essential to control the disease globally. Key prevention strategies include:

• BCG Vaccination: The Bacillus Calmette–Guérin (BCG) vaccine is widely used in many countries, especially where TB is prevalent. It provides partial protection against severe forms of TB, especially in children.
• Hygiene Measures: People with active TB should cover their mouths when coughing and wear a mask when around others to reduce transmission. Good ventilation is also important in crowded or poorly ventilated spaces.
• Prompt Treatment: Early diagnosis and treatment help prevent the spread of TB. Patients who adhere to their prescribed treatment regimen are less likely to transmit TB to others.
• Screening: Screening for TB is critical in high-risk groups such as healthcare workers, close contacts of TB patients, and people with weakened immune systems (e.g., HIV-positive individuals).

Global Impact

According to the World Health Organization (WHO), TB remains one of the deadliest infectious diseases globally. In 2020, an estimated 10 million people fell ill with TB, and 1.5 million people died from the disease. TB is particularly prevalent in Southeast Asia, sub-Saharan Africa, and the Western Pacific regions. The emergence of drug-resistant TB has compounded the challenge, leading to increased mortality and a need for more expensive and complex treatment regimens.

Challenges in TB Control

• Drug Resistance: Multi-drug-resistant (MDR-TB) and extensively drug-resistant (XDR-TB) tuberculosis continue to pose a significant global health threat. Effective control requires access to high-quality medicines, longer treatment regimens, and improved diagnostic methods.
• Co-infection with HIV: HIV and TB often co-occur, as HIV weakens the immune system, making it easier for TB to become active. Addressing both diseases simultaneously requires integrated healthcare services and treatment protocols.
• Social Determinants of Health: Poverty, malnutrition, and poor living conditions contribute to the spread of TB. Addressing these underlying social determinants is crucial for TB control.

Conclusion

Tuberculosis is a preventable and treatable disease, yet it remains a leading cause of death worldwide due to challenges in diagnosis, treatment, and prevention. Early detection, comprehensive treatment regimens, improved healthcare infrastructure, and effective vaccination programs are essential in reducing the burden of TB globally. Addressing the growing problem of drug resistance and co-infection with HIV will be crucial to improving TB control efforts and achieving the goal of ending the TB epidemic.