Page 15

lenge as it was a technical challenge led to there being a tuberculosis control program at the World Health Organization that in 1989 had a budget of approximately $2.5 million and a staff of only two professionals. The World Health Organization attitude and neglect fostered a similar neglect in developing countries.

The price of the neglect in the United States and abroad was a resurgence in the number of cases of tuberculosis in this country as well as in many other parts of the world and the development of multidrug-resistant tuberculosis. The resurgence of tuberculosis resulted in turn in a resurgence of interest in the elimination of and resources directed toward the elimination of tuberculosis that resulted in resumption in the decline of tuberculosis in the United States. This process was described as the “U-shaped curve of concern” (Reichman, 1991). The question yet to be answered is whether the renewed opportunity that now presents itself to move toward elimination of tuberculosis will be seized or whether tuberculosis will be subject to another period of neglect until the next resurgence.

TRANSMISSION AND PATHOGENESIS OF TUBERCULOSIS

Tuberculosis is spread from person to person through the air. When an individual with active tuberculosis of the respiratory tract, coughs, sneezes, yells, or sings, droplets that contain M. tuberculosis are expelled into the air. The largest of these particles quickly settle out of the air, but the smaller particles remain suspended, often for several hours. When inhaled, the larger particles are filtered in the upper airways or are deposited on the lining of the airways and are removed. However, droplets of approximately 1 to 5 µm in diameter can reach the alveoli, leading to infection. Macrophages in the lung usually engulf the bacilli in the alveoli, but unless specific immunity is present, the bacilli are often able to resist the attempts of the macrophage to kill them. The bacilli in macrophages begin to multiply and are transported to regional lymph nodes, enter the bloodstream, and can establish sites of infection throughout the body. The most common site where the tubercle bacilli establish an infection is the upper portions of the lungs, but the lymph nodes, kidneys, brain, and bones may also be affected. Within 2 to 10 weeks of the original infection a specific cell-mediated immunity usually develops. This immunity activates the macrophages and other immune cells, preventing further multiplication and spread of the bacilli. Individuals who have a successful immune response usually will have a positive tuberculin skin test but still harbor live tubercle bacilli in the parts of the body seeded by the early dissemination of the organism, so-called latent tuberculosis infection.

In latent tuberculosis infection the organisms are presumably capable



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement