What is tuberculosis?

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• Tuberculosis is caused by mycobacterium, usually Mycobacterium tuberculosis. The bacteria is transmitted from an infected host to a new host through respiratory mist. When a person with an active infection coughs, sneezes or spits, tiny droplets of moisture carrying the bacteria are released into the air, where they can be inhaled by another person. Inhaling even one mycobacterium tuberculosis bacterium can cause an infection.

Pathogenesis

• Once inhaled, the mycobacteria enter the lungs. When they reach the aveoli, they encounter macrophages, which are white blood cells that surround and digest pathogens. Sometimes, the immune system can destroy the mycobacteria, but if not, the mycobacteria begin multiplying within the macrophages. The macrophages are then used as transportation to nearby lymph nodes. Once in the lymph nodes, the mycobacteria can spread throughout the body.
  Because mycobacterium tuberculosis is a slow-growing bacteria, the immune system, if not able to destroy it, may be able to keep it from spreading enough to cause symptoms. This is called a latent tuberculosis infection, and it accounts for 90 percent of TB infections. While the organism might be present in the body for years, there is only a 10 percent chance that it will ever progress to an active infection. People with latent infections cannot spread TB to others.

Symptoms

• If tuberculosis progresses to an active infection, a productive cough, fever, fatigue and weight loss are likely first symptoms. If not treated, the infection may move to other parts of the body and cause painful lesions in the lungs, lymph nodes, brain, kidneys and bones. Once TB moves out of the lungs, it is referred to as extrapulmonary tuberculosis, and may affect the lympatic, skeletal, gastrointestinal, genitourinary or central nervous systems.Tuberculosis causes the death of healthy cells, and will result in the death of the patient if not treated with the appropriate antibiotics.