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Tuberculosis

vaccine bcg spread mycobacterium

Tuberculosis is a disease caused by the bacterium Mycobacterium tuberculosis. The organism infects the lungs and causes a debilitating condition that historically was known as consumption. In the 1970s, scientists considered tuberculosis as largely defeated following the widespread use of antibiotics. Today, multi-drug resistant Mycobacterium tuberculosis has developed, and tuberculosis has reemerged as a worldwide public health problem.

Tuberculosis is not a new disease. Indeed, examinations of Egyptian mummies that are over 4,000 years old have shown symptoms of tuberculosis. Hippocrates, the father of medicine, described a malady in 460 B.C. that he termed pthisis. His description makes it clear that he was describing tuberculosis.

The term consumption reflected the progression of tuberculosis. Patients became lethargic, weak, and seemed to waste away. The role of bacteria in tuberculosis became clear in 1882, when Robert Koch discovered a staining technique that allowed bacteria to be visible using a light microscope. In Koch's time, and even into the middle of the twentieth century, the main treatment for tuberculosis was the isolation of patients in facilities called sanitoriums. Here, patients spent much of their time exposed to the dry, fresh outdoor air, which lessened the spread of the bacteria.

Tuberculosis is infectious, and is spread from person to person via inhaling contaminated droplets in the air. Often, someone can be infected with Mycobacterium tuberculosis yet not feel ill. This is also called latent tuberculosis. The infected person can spread the germ to others, however, by coughing or breathing. An active infection can appear at a later time.

In the twentieth century, specific chemical treatments for tuberculosis were developed. French bacteriologists Leon Calmette and Camille Guérin found a way to grow Mycobacterium tuberculosis so that its ability to cause disease was weakened. This weakened, or attenuated, microbe eventually formed the basis of a vaccine. The bacille Calmette-Guérin (BCG) vaccine, which was first given to people in 1921, is still in use today.

Unfortunately, the potential of BCG has not been realized because the vaccine is protective against the form of tuberculosis that occurs in children rather than in adults. Also, because samples of the original vaccine were kept, the development of numerous formulations of BCG have made it difficult to establish which of the many variations of the vaccine is effective.

One variant of BCG, called Evans BCG, was withdrawn from use in July 2002 because of concerns that it was not protective against infection. Every vaccine, particularly those that use attenuated microorganisms, carries some risk. In the case of Evans BCG, the risks of its use were deemed to be greater than any benefit resulting from its use.

Beginning in the 1940s, antibiotics were discovered and chemically synthesized. An antibiotic called streptomycin was an immediate success against the tuberculosis bacteria. Unfortunately, resistance to the antibiotic soon developed. A succession of antibiotics was able to keep tuberculosis at bay for some decades. However, beginning in the 1980s, the number of cases of tuberculosis once again began to rise.

Some 30 million people around the world died of tuberculosis in the 1990s. The U.S. Department of Health and Human Services predicts tuberculosis, the "forgotten plague," will spread further by the year 2005. In 1990 there were 7,537,000 TB cases worldwide. That number is expected to rise by almost 60%, to 11,875,000 cases by 2005.

Part of this increase has paralleled the emergence and spread of Acquired Immunodeficiency Syndrome (AIDS). AIDS devastates the immune system, which gives other infections, including tuberculosis, a better chance to flourish. Another factor contributing to the spread of tuberculosis is the emergence of strains of Mycobacterium tuberculosis that are resistant to many antibiotics.

See also Epidemiology.


Resources

Books

Reichman, L.B., and J.H. Tanne. Time Bomb: The Global Epidemic of Multi-Drug Resistant Tuberculosis. New York: McGraw-Hill, 2001.

Periodicals

Starke, J.R., et al. "The Role of BCG Vaccine in the Prevention and Control of Tuberculosis in the United States: A Joint Statement by the Advisory Council for the Elimination of Tuberculosis and the Advisory Committee on Immunization Practices." Morbidity and Mortality Weekly Report 45 (April 1996): 1–18.


Organizations

Centers for Disease Control and Prevention. Division of Tuberculosis Elimination. 1600 Clifton Road, NE Mailstop E-10, Atlanta, GA 30333. (404) 639–8135. <http://www.cdc.gov/nchstp/tb/>.

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