Worlds of David Darling
Encyclopedia of Science
   
Home > Encyclopedia of Science

tuberculosis





A group of infectious diseases caused by the bacillus Mycobacterium tuberculosis. Tuberculosis (TB) was once common worldwide: in 1906 it killed 1 in every 500 persons in the US. Its incidence has fallen greatly and continues to fall in developed countries, although it remains a major problem in poorer nations.

TB may invade any organ but most commonly affects the respiratory system where it has been called consumption or phthisis. The disease is spread in three ways: inoculation via cuts, etc.; inhalation of infected sputum, and ingestion of infected food. In pulmonary TB there are two stages of infection. In primary infection there are usually no significant symptoms: dormant small hard masses called tubercles are formed by the body's defenses. In postprimary infection the dormant bacteria are reactivated due to weakening of the body's defenses and clinical symptoms become evident. These include fatigue, weight loss, persistent cough with green or yellow sputum and possibly blood.


Treatment

Modern drugs are highly effective against TB, although at least two different antibiotic drugs must be taken to avoid bacterial resistance to the drugs. A common treatment is three or four drugs daily for two months, followed by two drugs (usually isoniazid and rifampicin) for a further four to seven months. Complete recovery usually takes about two years.


Tuberculin tests

The tuberculin skin tests can show whether a person has some immunity to the disease, though the detection of the disease in its early stages, when it is readily curable, is difficult. Tberculin tests are carried out before BCG vaccination. A small amount of tuberculin purified protein from the bacteria) is injected into the skin. A few days later, the skin reaction, if any, is noted. A reaction indicates previous exposure, by infection or vaccination.


Prevention and control

Tuberculosis can be prevented by BCG vaccination, which is offered routinely at 10-14 years, or at birth for babies at high risk. Contacts of infected person are traced and, if necessary, are treated early to reduce the risk of the infection spreading.

Control of the disease is by preventive measures such as X-ray screening, BCG vaccination, isolation of infectious people, and sterilization.


Related category

   • HEALTH AND DISEASE