Tuberculosis also known as TB is a very infectious disease that affects the overall lungs. Tuberculosis bacteria spread very rapidly into the lungs as well as from person to person through literally tiny droplets released into the air by coughs and even sneezes. Many tuberculosis (TB) strains are resistant to the drugs most commonly used to treat the disease. People with active TB must take a variety of medications for months in order to clear the infection and avoid antibiotic resistance. Active tuberculosis symptoms include:

  • Coughing for three or more weeks
  • Coughing up blood or mucus
  • Chest pain, or pain with breathing or coughing
  • Unintentional weight loss
  • Fatigue
  • Fever
  • Night sweats
  • Chills
  • Loss of appetite

Tuberculosis can also affect other organs, such as the kidneys, spine, or brain. When TB occurs outside of your lungs, the signs and symptoms differ depending on the organs involved. For example, tuberculosis of the spine may cause back pain, while tuberculosis of the kidneys may result in blood in your urine.


Tuberculosis is caused by bacteria that spread from person to person via microscopic droplets in the air. When someone with untreated, active tuberculosis coughs, speaks, sneezes, spits, laughs or sings, this can happen. Tuberculosis is contagious. You are much more likely to contract tuberculosis from someone with whom you live or work than from a stranger. Most people with active tuberculosis who have received adequate drug treatment for at least two weeks are no longer contagious.


Tuberculosis can be fatal if not treated. The untreated active disease usually affects your lungs, but it can also affect other parts of your body. Complications of tuberculosis include:

  • Back pain. Back pain and stiffness are common tuberculosis complications.
  • Damage to the joints. Tuberculous arthritis (arthritis caused by tuberculosis) typically affects the hips and knees.
  • The membranes that cover your brain swell (meningitis). This can result in a persistent or intermittent headache that lasts for weeks, as well as mental changes.
  • Problems with the liver or kidneys. Your liver and kidneys aid in the removal of waste and impurities from your bloodstream. Tuberculosis can impair the function of these organs.
  • Heart problems in rare cases, tuberculosis can infect the tissues surrounding your heart, causing inflammation and fluid accumulation that can impair your heart's ability to pump affectively.


TB infection occurs in four stages, with tuberculosis affecting the lungs in each stage. The stages are the initial macrophage response, growth, immune control, and lung cavitation. These four stages take about a month to complete.

Stage One

The first stage occurs within the first week of inhaling the TB bacillus. After the bacillus enters the lung's alveoli, it is picked up by immune system cells known as macrophages. These macrophages are normally found within the alveolar tissue; their job is to swallow and inactivate any foreign object that enters the alveolar space macrophages swallow the TB bacillus The events that follow are largely determined by the number of TB bacilli present and the strength of the macrophage. The bacilli can reproduce in macrophages if the amount of TB bacilli is too large or if the macrophage is not strong enough to resist them. This eventually leads to the macrophage's destruction and the infection of new, nearby macrophages that try to swallow emerging TB bacilli.

Stage Two

If the macrophage is unable to contain the TB bacillus, the infection progresses to the second stage after about a week. The TB bacilli begin to reproduce exponentially, which means that for every original bacillus, two new ones emerge. These two then produce two more, and so on. This causes the initial TB bacillus to rapidly multiply, and the macrophages are unable to stop the spread. This stage lasts until the third week following infection.

Stage Three

After the third week, the bacilli no longer grow exponentially, and the infection enters its third stage, where bacilli growth and destruction by macrophages appear to be balanced. The body sends more immune cells to the site to help stabilize it, and the infection is under control. At least nine out of ten Mycobacterium tuberculosis patients die at stage 3 and show no symptoms or physical signs of active disease. The TB bacilli and macrophages that swallowed them form a round complex in their lungs, with TB bacilli and infected macrophages in the center and healthy macrophages surrounding them. This is known as a Ghon focus, after the Austrian pathologist who described it first. TB bacilli frequently infect the surrounding lymph nodes. The primary complex is made up of a complex in the lung tissue and an infected local lymph node.

The TB bacilli are protected from the lung tissue, but they can survive in macrophages for years. Patients in this stage are not contagious because the TB bacilli cannot enter the airways and cannot be coughed up or exhaled. If the immune system is strong, the primary complex heals and leaves only a small cavity and a scar in the tissue. This scar, which can later be seen on X-rays, indicates that the person was infected with Mycobacterium tuberculosis.

Stage Four

The primary complex does not heal in about half of the cases, and the TB bacilli reactivate 12 to 24 months after the initial infection: this is stage 4 of the infection. The reactivated tuberculosis bacilli multiply rapidly and form a cavity in the tissue where the immune system cannot reach them. The TB bacilli quickly spread through the tissue from this cavity, and the person develops active TB symptoms such as coughing. The person is highly contagious at this stage because his or her sputum contains active tuberculosis bacteria. Reactivation is more likely when the immune system is compromised, as in HIV infection or malnutrition.

In summary, the body responds to Mycobacterium tuberculosis infection in three ways:

  • If the body's immune system is strong, lymphocytes can contain the bacteria and prevent the infection from spreading.
  • If the immune system is weakened, the lymphocytes are unable to contain the TB bacteria, and it spreads rapidly. The infected person becomes ill and develops symptoms.
  • If the immune system is initially strong and contains the TB bacteria, but then weakens and can no longer control it, the bacteria first go dormant but then become reactivated and spread aggressively. It can also be triggered by a new infection with TB bacteria, which causes the initial infection to reactivate.


Tuberculosis (TB) is a bacterial infection of the lungs that can cause a variety of symptoms such as chest pain, shortness of breath, and severe coughing. If a person does not receive treatment for pulmonary tuberculosis, it can be fatal. Bacteria can be spread through the air by tuberculosis. However, in order to become infected, a person must be in close contact for an extended period of time.