Tuberculosis (TB) Facts (cont.)

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What is tuberculosis?

Tuberculosis (TB) is a multisystemic infectious disease caused by Mycobacterium tuberculosis, a rod-shaped bacterium. TB is the most common cause of infectious disease-related mortality worldwide (about 1.1 million to 1.7 million people die from it each year worldwide). TB symptoms can be so diffuse that TB is termed the "great imitator" by many who study infectious diseases because TB symptoms can mimic many different diseases. Additional terms are used to describe TB. The terms include consumption, Pott's disease, active, latent, pulmonary, cutaneous, and others (see the following section), and they appear in both medical and nonmedical publications. In most instances, the different terms refer to a specific type of TB with some unique symptoms or findings. The most common site (about 85%) for TB to develop is in the pulmonary tract. Humans are the only known hosts for Mycobacterium tuberculosis (although animals can get infected).

TB has likely been infecting humans for many centuries; evidence of TB infections has been found in cadavers that date back to about 8000 BC, so the disease has a long history of infecting humans. The Greeks termed it as a wasting away disease (phthisis). For many European countries, TB caused death in about 25% of adults and was the leading cause of death in the U.S. until the early 1900s. Robert Koch discovered TB's cause, Mycobacterium tuberculosis, in 1882. With increased understanding of TB, public-health initiatives, treatment methods like isolation (quarantine), and the development of drugs to treat TB, the incidence of the disease, especially in developed countries, has been markedly reduced.

There is a vast amount of detailed information available in the medical literature on all aspects of this potentially debilitating and lethal disease. The goal of this article is to introduce the reader to TB and help them to obtain a general knowledge about TB's cause, transmission, diagnostic tests, treatments, and prevention methods.

Are there different types of tuberculosis (TB)?

There are many types of tuberculosis, but the main two types are termed either active or latent TB. Active TB is when the disease is actively producing symptoms and can be transmitted to other people; latent disease is when the person is infected with Mycobacterium tuberculosis bacteria, but the bacteria are not producing symptoms (usually due to the body's immune system suppressing the bacterial growth and spread). People with latent TB usually cannot transfer Mycobacterium tuberculosis bacteria to others unless the immune system fails; the failure causes reactivation (bacterial growth is no longer suppressed) that results in active TB so the person becomes contagious.

Many other types of TB exist in either the active or latent form. These types are named for the signs and for the body systems Mycobacterium tuberculosis preferentially infect, and these infection types vary from person to person. Consequently, pulmonary TB mainly infects the pulmonary system, cutaneous TB has skin symptoms, while miliary TB describes widespread small infected sites (lesions or granulomas about 1 mm-5 mm) found throughout body organs. It is not uncommon for some people to develop more than one type of active TB. More types will be listed in the symptoms and signs section below.

Medically Reviewed by a Doctor on 12/8/2014

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