Tuberculosis or TB, is an infectious disease caused by a microorganism called Mycobacterium tuberculosis. It can affect many different parts of the body, although it usually infects the lungs. Tuberculosis in the lungs is called pulmonary tuberculosis. The first stage lasts for several months. The immune system resists TB during this stage. Most of the bacteria are walled in by a fibrous capsule that forms around it. A few will make it to the bloodstream where they will be eventually walled in. Most cases never develop beyond this stage. This is known as TB infection. .
If the immune system is not able to stop the infection and the bacteria not treated, the bacteria begin the second stage. During this stage, the bacteria reproduce quickly and destroy the lung tissues. TB usually results in a much smaller respiratory capacity, which in turn makes physical exercise difficult. This stage usually begins if a person's immune system is low.
During the first stage, the person may have no symptoms at all. They may have a flu-like illness though. The first stage is usually found in the middle or lower lung. There it reproduces and spreads into the lymph nodes. From here it has access to the bloodstream. .
During the second stage, though, it becomes much worse. Symptoms may be a fever, night sweats, weight loss, and fatigue. Pulmonary TB, however, gives a dry, non-mucous cough and is followed by bloodstained sputum when you cough. You also have chest pain and shortness of breath. During this stage, the bacteria are very contagious. .
TB is carried in the air and enters the body through the nose or mouth. A person with second stage pulmonary TB spreads the disease when coughing or sneezing. So, in order to become infected, a person would come in close contact with another person that had second stage TB. You can also get TB from unpasteurized milk and other dairy products from infected cows. The rarest way of getting TB is transmitted by infected urine.