TUBERCULOSIS

Tuberculosis is a widespread and in many cases fatal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis.Tuberculosis typically attacks the lungs, but can also affect other parts of the body. It is spread through the air when people who have an active TB infection cough, sneeze, or otherwise transmit respiratory fluids through the air.Most infections do not have symptoms, known as latent tuberculosis. About one in ten latent infections eventually progresses to active disease which, if left untreated, kills more than 50% of those so infected.

Signs and Symptoms

Extrapulmonary TB occurs when tuberculosis develops outside of the lungs, although extrapulmonary TB may coexist with pulmonary TB, as well.

General signs and symptoms include fever, chills, night sweats, loss of appetite, weight loss, and fatigue.Significant nail clubbing may also occur.

CAUSES

The main cause of TB is Mycobacterium tuberculosis, a small, aerobic, nonmotile bacillus.The high lipid content of this pathogen accounts for many of its unique clinical characteristics.It divides every 16 to 20 hours, which is an extremely slow rate compared with other bacteria, which usually divide in less than an hour. Mycobacteria have an outer membrane lipid bilayer.If a Gram stain is performed, MTB either stains very weakly Gram positive or does not retain dye as a result of the high lipid and mycolic acid content of its cell wall.MTB can withstand weak disinfectants and survive in a dry state for weeks. In nature, the bacterium can grow only within the cells of a host organism, but M. tuberculosis can be cultured in the laboratory.

TRANSMISSION

When people with active pulmonary TB cough, sneeze, speak, sing, or spit, they expel infectious aerosol droplets 0.5 to 5.0 µm in diameter. A single sneeze can release up to 40,000 droplets.Each one of these droplets may transmit the disease, since the infectious dose of tuberculosis is very small (the inhalation of fewer than 10 bacteria may cause an infection.

PREVENTION

Tuberculosis prevention and control efforts primarily rely on the vaccination of infants and the detection and appropriate treatment of active cases.The World Health Organization has achieved some success with improved treatment regimens, and a small decrease in case numbers.

VACCINES

The only available vaccine as of 2011 is bacillus Calmette-Guérin.In children it decreases the risk of getting the infection by 20% and the risk of infection turning into disease by nearly 60%.