When a microorganism infects a person's body, he or she usually becomes sick within one to two weeks, but not with tuberculosis. Except for very young children, people can have live bacteria "sleeping" inside their bodies for many years. The body's defense mechanisms prevented the bacteria from developing into full-scale tuberculosis, but have not killed the bacteria. These sleeping bacteria cannot be spread to other people.
In the vast majority of people, the bacteria never cause problems. In five to 10 percent, however, the bacteria start to multiply and develop tuberculosis, usually within the first two years after infection. Although what causes the bacteria to become active is not known, it can happen because of an immune system weakened by advanced age, the use of corticosteroids or AIDS.
In this phase, an infected person feels sick and can spread the disease to other people. The bacteria that cause tuberculosis can live only in people. It cannot be carried by animals, insects, soil or nonliving objects. The bacteria spread only through the air when a person coughs, sneezes or speaks. The bacteria can stay in the air for several hours, making it possible for many other people to become infected with tuberculosis.
The signs of tuberculosis may not appear to be serious at first. They include:
- Coughing, which produces a small amount of green or yellow sputum in the morning. As the disease gets worse, the sputum may be streaked with small amounts of blood.
- Cold night sweats, which are heavy enough to wake a sleeper up and require a change of nightclothes or bed sheets
- Not feeling well in general
- A loss of energy and appetite
- Weight loss over time
- Sudden shortness of breath along with chest pain may be a sign that air or fluid has entered the space between the lungs and the chest wall (pneumothorax). For many people this is the first sign that leads them to seek a diagnosis.
When a tuberculosis infection first occurs, the bacteria may travel from the lungs to the lymph nodes that drain the lungs. If the body is able to bring the infection under control at this stage, the bacteria become dormant.
A dangerous complication for young children, whose immune systems are weaker and bodies are smaller, is that the lymph nodes can swell large enough to press on the bronchial tubes, causing a cough and possibly a collapsed lung. Sometimes, the bacteria spread up the lymph system to the lymph nodes in the neck, in which case, the infection may break through the skin and let loose pus.
In people with a fully functioning immune system, active tuberculosis is usually limited to the lungs (pulmonary tuberculosis). Tuberculosis that affects other parts of the body (extrapulmonary tuberculosis) comes from pulmonary tuberculosis that has spread through the blood. As in the lungs, the infection may not cause disease, but the bacteria may remain dormant in a very small scar. Latent organisms in these scars can reactivate later in life, leading to symptoms in the organs involved. In pregnant women, the tuberculosis bacteria may spread to the fetus and cause disease; however, such congenital tuberculosis is uncommon. If the tuberculosis infection occurs outside the lungs, it usually affects the kidneys and the lymph nodes. Symptoms of a tuberculosis infection elsewhere than the lungs tend to be vague and include:
- Poor appetite
- Fevers that come and go
- Weight loss in some cases
Other types of tuberculosis include:
- Tuberculosis meningitis, which affects the tissues that cover the brain. This is life threatening. Symptoms include fever, a headache that does not go away, stiffness in the neck, nausea and sleepiness that can develop into a coma.
- Tuberculoma, which affects the brain itself and forms a mass that causes headaches, seizures or muscle weakness
- Tuberculous pericarditis, which affects the membrane that covers the heart (pericardium). This type of tuberculosis causes the pericardium to thicken. Sometimeswhich affects the membrane that covers the heart (pericardium). This type of tuberculosis causes the pericardium to thicken. Sometimes fluid will leak from the layers of the pericardium into the space between the pericardium and the heart, making it harder for the heart to pump. It can cause swollen veins in the neck and difficulty breathing.
- Intestinal tuberculosis, which may not cause any symptoms but does create an abnormal mass of tissue that can be mistaken for cancer
- Miliary tuberculosis, which is a life-threatening type of tuberculosis that occurs when a large number of bacteria are spread throughout the body in the bloodstream. It gets its name from the millions of tiny lesions formed, which are the size of millet, a tiny round seed. If it gets into the bone marrow, it can cause severe anemia and blood conditions that seem like leukemia.
Causes and Risk Factors
In the United States and other developed countries, tuberculosis is more likely to affect older people. In poorer countries, it is a disease of young adults. People of European ancestry are somewhat less likely to get tuberculosis because the bacterium for it has existed a long time in Europe. People from other parts of the world, where tuberculosis is a newer disease, are at greater risk of developing it. In the United States, tuberculosis is more common among African Americans, Native Americans and immigrants from non-European countries.
Poverty, poor nutrition, crowded living conditions, exposure to tuberculosis and lack of access to medical care all increase the risk of developing tuberculosis.