Tuberculosis is a contagious, airborne, bacterially transmitted disease. If untreated, it is invariably fatal. It has been known since ancient times, but effective treatments have only been available since the early 20th century.
Tuberculosis is caused by mycobacteria, mainly the species Mycobacterium tuberculosis, which were first isolated by Robert Koch in the late 19th century. The bacteria is transmitted when a carrier or an infected patient coughs or sneezes, carrying small droplets of the bacteria which are then inhaled by others. In most people, the immune system can fight off the bacteria quite quickly and they never become seriously infected. However, in some people, the bacteria becomes established in the lungs and spreads from there to the rest of the body.
Although the immune system attempts to fight off tuberculosis, the disease has the ability to go into a period of dormancy where the disease hides in parts of the lung that are not accessible to the bloodstream and immune system. This characteristic of the disease also makes antibiotic therapy difficult, as during the dormant period the disease is also inaccessible to the effect of antibiotics.
In addition, tuberculosis mutates quite frequently in the body and can quickly become resistant to the antibodies the immune system sends to fight it, as well as becoming resistant to any single type of antibiotic. As a result, modern therapy requires the use of three different antibiotics over a six month period in order to insure that the bacteria is treated while it is active in the bloodstream.
Tuberculosis is very contagious and historically patients had to be treated in special hospitals in order to isolate them from other hospital patients, who would certainly become infected if they had any contact with the disease. However, patients with active tuberculosis can now be treated in isolation in general hospitals without fear of contagion to other patients.
Many forms of tuberculosis have become resistant to multiple antibiotics and are difficult or impossible to treat. Resistant strains types include 'Multi Drug Resistant Tuberculosis' (MDR-TB) and 'Extensively Drug Resistant Tuberculosis' (XDR-TB). Patients with these strains must be isolated to prevent the disease from spreading.
Tuberculosis is very rare in the Americas and Europe due to dedicated health care programs to isolate and properly treat the disease. Most new cases come from areas of the world where the disease is endemic. However, new immigrants and AIDS patients are particularly susceptible to tuberculosis and suffer from it at a rate far in excess of the general population.
Tuberculosis is quite common in the developing world and the combination of antibiotics needed to treat it are generally too expensive for a patient to receive proper treatment.