CDC Logo Tuberculosis Information CD-ROM   Image of people
jump over main navigation bar to content area
TB Guidelines
Surveillance Reports
Slide Sets
TB-Related MMWRs and Reports
Education/Training Materials
Ordering Information


U.S. Department of Health and Human Services


Education Materials > Publications > Self-Study Modules on TB > Module 1 > Background

Self-Study Modules on Tuberculosis

This is an archived document. The links are no longer being updated.


Module 1: Transmission and Pathogenesis


In this module, you will learn about the history of tuberculosis (TB). You will also learn how TB is spread from person to person (transmission) and how TB disease develops in the body (pathogenesis). Our understanding of the transmission and pathogenesis of TB has guided us in developing strategies for controlling the spread of TB and for treating TB infection and disease. As a public health worker, you should understand these concepts so that you can educate the patients you serve.


After working through this module, you will be able to:

  1. Briefly describe the history of TB.
  2. Explain how TB is spread (transmission).
  3. Explain the difference between TB infection and TB disease.
  4. Explain how TB infection and TB disease develop (pathogenesis).
  5. List risk factors for the development of TB disease.
  6. Describe how human immunodeficiency virus (HIV) infection affects the pathogenesis of TB.
  7. Describe the classification system for TB.

New Terms

Look for the following new terms in this module and in the glossary.

AIDS acquired immunodeficiency syndrome, a disease in which the immune system is weakened and therefore less able to fight certain infections and diseases; AIDS is caused by infection with the human immunodeficiency virus (HIV)

alveoli the small air sacs of the lung that are at the end of the airway; when droplet nuclei reach these air sacs, TB infection begins

corticosteroid a type of steroid, either natural or man-made, often used to treat arthritis or certain allergies

diabetes mellitus a disease in which the body's ability to use sugar is weakened

droplet nuclei very small droplets (1 to 5 microns in diameter) that may be expelled when a person who has infectious TB coughs or sneezes; they can remain suspended in the air for several hours, depending on the environment

drug injection using a needle and syringe to inject drugs into the body

extrapulmonary TB TB disease that occurs in places other than the lungs, such as the lymph nodes, the pleura, the brain, the kidneys, or the bones; most types of extrapulmonary TB are not infectious

HIV human immunodeficiency virus, the virus that causes AIDS

immune system cells and tissues in the body that protect the body from foreign substances

immunosuppressive therapy therapy that suppresses, or weakens, the immune system

infectious capable of spreading infection; a person who has infectious TB disease expels droplets containing M. tuberculosis into the air when he or she coughs or sneezes

miliary TB TB disease that occurs when tubercle bacilli enter the bloodstream and are carried to all parts of the body, where they grow and cause disease in multiple sites; the chest x-ray of patients with miliary TB often looks like millet seeds scattered throughout the lung

mycobacteria a kind of bacteria; mycobacteria can cause a variety of diseases

Mycobacterium africanum a type of tuberculous mycobacteria, closely related to M. tuberculosis, that can cause a disease similar to TB in humans; it is very rare in the United States

Mycobacterium avium complex a common type of nontuberculous mycobacteria that can cause disease in humans

Mycobacterium bovis a type of tuberculous mycobacteria that can cause a disease similar to TB in cows. Before the pasteurization of milk became common practice, these mycobacteria were often spread to humans through contaminated milk; in the United States today, M. bovis rarely affects humans

Mycobacterium tuberculosis the organism that causes TB in humans and is sometimes called the tubercle bacillus; belongs to a group of bacteria called mycobacteria

nontuberculous mycobacteria mycobacteria that do not cause TB disease and are not usually spread from person to person; one example is M. avium complex

pathogenesis how an infection or disease develops in the body

pulmonary TB TB disease that occurs in the lungs (about 85% of all U.S. cases), typically causing a cough and an abnormal chest x-ray; pulmonary TB is usually infectious if untreated

silicosis a lung disease caused by inhaling silica dust, which is used in the production of glass and ceramics; occurs most often in mining and foundry workers

transmission the spread of an organism, such as M. tuberculosis, from one person to another; depends on the contagiousness of the patient, the type of environment, and the length of exposure

tubercle bacilli another name for Mycobacterium tuberculosis organisms, which cause TB disease

tuberculin skin test a test used to detect TB infection (see Mantoux tuberculin skin test or multiple-puncture test in glossary)

tuberculous mycobacteria mycobacteria that can cause TB disease or other diseases very similar to TB; the tuberculous mycobacteria are M. tuberculosis, M. bovis, and M. africanum


Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
Division of Tuberculosis Elimination -

Please send comments/suggestions/requests to:, or to
CDC/Division of Tuberculosis Elimination
Communications, Education, and Behavioral Studies Branch
1600 Clifton Rd., NE - Mailstop E-10, Atlanta, GA 30333