Tuberculosis is a disease caused by Mycobacterium tuberculosis which requires a high degree of oxygenated tissue in which to grow. This means that once the bacterium enters the body it usually chooses to grow in the upper lobes of the lungs, liver, kidney and brain.
Individuals can catch tuberculosis by breathing droplets in the air that contain the bacteria. These droplets are usually spread when someone with tuberculosis coughs, sneezes, or laughs. Although its spread through the air, many people need to be exposed to a person for a period of time before catching it. This means that the people who most commonly catch tuberculosis catch it from people they will live with or work with.
The one instance where this may not be true is in individuals who have immune mediated illnesses or diseases which compromised or immune system. Because their immune systems are compromised, such as in AIDS or severe diabetes, their bodies are more at risk for developing the disease more quickly.
The very young and the very old are also at greater risk for developing tuberculosis. Those who are malnourished or who smoke or drink excessively will also have a greater risk. Individuals who plan to travel to countries where tuberculosis is at a higher incidence should be aware that this increases their risk of developing the disease.
Once an individual breathes in an a tiny droplet of saliva or mucus that carries the bacteria the bacteria will travel to the alveoli. These are small sack like structures in the air spaces of the lungs. There another cell called the macrophage will swallow up the tuberculosis bacteria.
At this point the bacteria can grow within the lungs and also be transmitted to the lymphatic system and bloodstream where it can spread to other organs. When the bacteria has grown enough in numbers to cause clinically detectable disease and individual is said to have tuberculosis.
People who have inhaled the tuberculosis bacteria but who have no evidence of active disease are said to have latent tuberculosis. The immune system may have walled off the organism in an inflammatory locus known as a granuloma. These individuals will frequently have a positive TB skin test but will not be able to transmit the disease to others.
Tuberculosis is not as highly contagious when compared to some other infectious diseases. Only about one in three people who are in close contact with a patient who has active tuberculosis will become infected. Unlike other infections, tuberculosis is not passed through contact with clothing, bed linens, dishes are cooking utensils but rather only through droplets which carry the active disease and are inhales by another individual..
Since the 1980s the number of individuals who have been diagnosed with tuberculosis has increased dramatically because of the spread of HIV. Tuberculosis and HIV have a deadly relationship because each drives the progress of the other. Infections with HIV will suppress the immune system and make it more difficult for individuals to control tuberculosis bacteria. As a result, individuals who suffer from AIDS and HIV are many times more likely to get tuberculosis than those who don’t.
Another reason that tuberculosis remains a major killer both in the United States and outside the United States, is the increase in drug resistant strains of the bacteria. The bacteria has developed the ability to survive the antibiotics and the ability to pass that ability to the next generation of bacteria. The surviving bacteria become resistant to drugs which is the major reason that for antibiotics are used in the initial two month treatment of the disease.