What is tuberculosis?
Tuberculosis (TB) is a contagious, wasting disease caused by any of several mycobacteria. The most common form of the disease is tuberculosis of the lungs (pulmonary consumption, or phthisis), but the intestines, bones and joints, the skin, and the genitourinary, lymphatic, and nervous systems may also be affected. Tuberculosis is an infectious disease caused
by the microorganism Mycobacterium tuberculosis. It can affect several organs of the human body, including the brain, the kidneys and the bones; but most commonly it affects the lungs (Pulmonary Tuberculosis).
Tuberculosis is an infection, with or without disease, caused by the bacterium Mycobacterium tuberculosis. Humans usually acquire infection by breathing in infectious droplets, which have been expelled from the respiratory tract of infected persons. Tuberculosis disease mainly affects and damages the lungs, but the bacterium may spread to any other organ system. The disease is slowly progressive and chronic if untreated and death may result. Treatment with antibiotics is available, but must be administered over many months to achieve remission. TB primarily infects the lungs, but it may attack almost any tissue or organ of the body. TB generally has a long latency period, and only about 10% of infected people with normal immunity ever experience active TB. For people with immune deficiencies, active TB is much more common. TB is transmitted in close quarters when a person with active TB coughs the microbe into the air.
There are three major types of tubercle bacilli that affect humans. The human type (Mycobacterium tuberculosis), first identified in 1882 by Robert Koch, is spread by people themselves. It is the most common one. The bovine type (M. bovis) is spread by infected cattle but is no longer a threat in areas where pasteurization of milk and the health of cattle are strictly supervised. The avian type (M. avis) is carried by infected birds but can occur in humans. The tubercle bacillus can live for a considerable period of time in air or dust. The most common means of acquiring the disease is by inhalation of respiratory droplets.
The first stage of the infection usually lasts for several months. During this period, the body's natural defenses (immune system) resist the disease, and most or all of the bacteria are walled in by a fibrous capsule that develops around the area. Before the initial attack is over, a few bacteria may escape into the bloodstream and be carried elsewhere in the body, where they are again walled in. In many cases, the disease never develops beyond this stage - and is referred to as TB infection. If the immune system fails to stop the infection and it is left untreated, the disease progresses to the second stage, active disease. There, the germ multiplies rapidly and destroys the tissues of the lungs (or the other affected organ). In some cases, the disease, although halted at first, flares up after a latent period. Sometimes, the latent period is many years, and the bacteria become active when the opportunity presents itself, especially when immunity is low. The second stage of the disease is manifested by destruction or "consumption" of the tissues of the affected organ. When the lung is affected, it results in diminished respiratory capacity, associated with other symptoms; when other organs are affected, even if treated adequately, it may leave permanent, disabling scar tissue.
TB spreads through airborne droplets when a person with the infection coughs, talks or sneezes. In general, you need prolonged exposure to an infected person before becoming infected yourself. Even then, you may not develop symptoms of the disease. Although your body harbors the TB bacteria, your immune system often can prevent you from becoming sick. For that reason, doctors make a distinction between being infected with TB, which causes no symptoms and isn't contagious, and having active TB, which makes you sick and can spread to others.
Tuberculosis of the lungs usually results in no or minimal symptoms in its early stages. In most persons the primary infection is contained by the body's immune system, and the lesion, called a tubercle, becomes calcified. In many the infection is permanently arrested. In others the disease may break out again and become active years later, usually when the body's immune defenses are low. Untreated, the infection can progress until large areas of the lung and other organs are destroyed. Symptoms of the disease include cough, sputum, bleeding from the lungs, fever, night sweats, loss of weight, and weakness.
Many people infected with tuberculosis have no symptoms because it is dormant. Once active, tuberculosis may cause damage to the lungs and other organs. Active tuberculosis is also contagious and is spread through inhalation. Treatment of tuberculosis involves taking antibiotics and vitamins for at least 6 months. |
