Tuberculosis (TB) is an infectious disease that is caused by a bacterium (bac’te’ri’um) called Mycobacterium (my’co’bac’te’ri’um) tuberculosis. TB mostly affects the lungs, but it can also affect organs in the central nervous system, lymphatic system, and circulatory system among others. The disease was called "consumption" in the past because of the way it would consume from within anyone who became infected.
When a person is infected with TB, the bacteria in the lungs multiply and along cause Pneumonia with chest pain, coughing up blood, and is always coughing. Also, lymph nodes near the heart and lungs become big. As the TB tries to spread to other parts of the body, it is often broken up by the body's immune system. The immune system forms scar tissue (fibrosis) around the TB bacteria, and this helps fight the infection and prevents the disease from spreading all over the body and to other people. If the body's immune system is not to fight TB or if the bacteria breaks through the scar tissue, the disease returns to an active state with pneumonia and damage to kidneys, bones, and the meningitis that line the spinal cord and brain.
TB is generally classified as being either inactive or active. Inactive TB occurs when the bacteria are present in the body, but this state is not active and shows no symptoms. Inactive TB is also not contagious. Active TB is contagious and is the condition that can make you sick with symptoms.
TB is a major cause of illness and death worldwide, especially in Africa and Asia. Each year the disease kills almost 2 million people. The disease is also common among people with HIV/AIDS.