What is tuberculosis (TB)?
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.
