TB is an infectious disease usually caused by Mycobacterium tuberculosis (MTB) bacteria. It generally affects the lungs, but can also affect other parts of the body.
Most infections do not have symptoms = latent tuberculosis.
It was historically called “consumption” due to the weight loss.
Infection of other organs can cause a wide range of symptoms.
Spread through the air via cough, spit, speak, or sneeze
Active infection occurs more often in smokers and people with HIV/AIDS
Diagnosis requires chest X-rays, microscopic examination and culture of body fluids
One-quarter of the world’s population is thought to be infected with TB
Classic clinical features associated with active pulmonary TB:
Chest pain (can also result from tuberculous acute pericarditis)
Symptoms of tuberculous meningitis may include:
Headache that has been either intermittent or persistent for 2-3 weeks
Subtle mental status changes that may progress to coma over a period of days to weeks
Low-grade or absent fever
Mycobacteria reach the alveolar air sacs and invade and replicate within endosomes of alveolar macrophages.
Macrophages identify the bacterium as foreign and attempt to eliminate it by phagocytosis.
The bacterium is enveloped by the macrophage and stored temporarily in a membrane-bound vesicle called a phagosome.
The phagosome then combines with a lysosome to create a phagolysosome.
In the phagolysosome, the cell attempts to use reactive oxygen species and acid to kill the bacterium.
However, M. tuberculosis has a thick, waxy mycolic acid capsule that protects it from these toxic substances.
M. tuberculosis is able to reproduce inside the macrophage and will eventually kill the immune cell.
MDR-TB is defined as resistance to isoniazid and rifampin, which are the 2 most effective first-line drugs for TB. In 2006, an international survey found that 20% of M tuberculosis isolates were MDR.
The cure rate in persons with MDR-TB is 50-60%, compared with 95-97% for persons with drug-susceptible TB.
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