What causes tb in lungs

What Causes TB in the Lungs?

Tuberculosis (TB) is an infectious disease that most often affects the lungs. It is caused by a specific type of bacteria known as Mycobacterium tuberculosis. While TB can affect other parts of the body, pulmonary TB, affecting the lungs, is the most common and the primary source of transmission.

The Culprit: Mycobacterium tuberculosis

Mycobacterium tuberculosis is a slow-growing bacterium that thrives in areas of the body with a rich blood supply and high oxygen content, making the lungs an ideal environment. These bacteria are microscopic and can only be seen with a microscope. They are resistant to drying out and can survive for some time outside the body, although they are sensitive to ultraviolet light and heat.

How TB Spreads: An Airborne Threat

The primary mode of transmission for TB is through the air. When an individual who has active pulmonary TB coughs, sneezes, speaks, laughs, or sings, they release tiny droplets containing the Mycobacterium tuberculosis bacteria into the air. These droplets can remain suspended in the air for several hours. Other people can become infected if they inhale these airborne droplets.

It is important to understand that not everyone infected with TB bacteria will develop active TB disease. The infection typically occurs in two stages:

1. Latent TB Infection (LTBI)

In most cases (about 90% of infected people), the body's immune system successfully fights off the bacteria. The immune system forms a barrier around the bacteria, preventing them from multiplying and causing illness. This state is known as latent TB infection (LTBI). People with LTBI do not feel sick, do not have symptoms, and cannot spread the bacteria to others. However, the bacteria remain alive in the body and could become active later.

2. Active TB Disease

In a smaller percentage of people (about 10% of infected people), the immune system cannot keep the bacteria under control, and the infection progresses to active TB disease. This usually happens within weeks or months of infection, but it can also occur years later, especially if the person's immune system weakens. When TB becomes active in the lungs, the bacteria multiply, and the person develops symptoms and can spread the disease to others.

Factors Influencing TB Transmission and Development

Several factors influence whether a person becomes infected after exposure to TB bacteria and whether that infection progresses to active disease:

• Type and Duration of Exposure: Close, prolonged contact with someone who has active pulmonary TB increases the risk of infection. Brief exposure, such as walking past someone in a hallway, is less likely to result in infection.
• Infectiousness of the Source Case: The number of bacteria present in the sputum (phlegm) of the person with active TB plays a significant role. Individuals with a high bacterial load are more contagious.
• Environmental Factors: Poorly ventilated indoor spaces can allow airborne droplets to concentrate, increasing the risk of transmission.
• Host Immune Status: The strength of an individual's immune system is crucial. People with weakened immune systems are at a higher risk of developing active TB disease if infected. Conditions that weaken the immune system include:
  • HIV infection
  • Diabetes
  • Cancer
  • Malnutrition
  • Certain medications (e.g., corticosteroids, chemotherapy)
  • Organ transplantation

Symptoms of Active Pulmonary TB

When TB bacteria become active in the lungs, they damage lung tissue and can cause symptoms such as:

• A persistent cough, sometimes with phlegm or blood
• Chest pain
• Fever
• Night sweats
• Unexplained weight loss
• Fatigue
• Loss of appetite

Prevention and Treatment

Preventing the spread of TB involves early diagnosis and treatment of individuals with active TB disease. Public health measures, such as contact tracing and ensuring access to healthcare, are vital. For those exposed, preventive treatment may be recommended to prevent latent infection from becoming active disease. Treatment for active TB involves a course of specific antibiotics, typically lasting several months.

In summary, TB in the lungs is caused by the bacterium Mycobacterium tuberculosis, which spreads through the air from person to person. While infection doesn't always lead to disease, factors like immune status and exposure intensity influence the risk of developing active TB.