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BACKGROUND REPORT MARCH 19, 2009
Tuberculosis
Tuberculosis is a chronic bacterial
infection that spreads through the air and primarily affects the lungs.
If not treated properly, tuberculosis can affect other organs and lead
to death.
Tuberculosis, or TB, has been
infecting humans for thousand of years; evidence of tuberculosis has
been found in the spines of Egyptian mummies, and it was present in
ancient Greece and Rome. Despite advances in treatment, it remains a
major cause of illness and death worldwide.
More than 2 billion people
-- a third of the world's population -- are infected with TB bacilli,
the microbes that cause the disease. An estimated 1.7 million people
died from TB in 2006.
The annual incidence rate peaked
in 2003 and 2004, but the total number of deaths and cases continues
to grow as the global population does. Rates of tuberculosis have increased
since the 1980s, fueled by the HIV/AIDS epidemic and the emergence of
drug-resistant strains of TB bacteria that are harder to treat.
In 2006, HIV-related tuberculosis
killed 200,000 people, according to the World Health Organization.
Tuberculosis is caused by a
bacterium, Mycobacterium tuberculosis, which spreads through microscopic
droplets in the air. When a person infected with TB coughs, sneezes
or talks, they can release these droplets into the air.
Breathing the bacteria into the lungs does not always result in an infection,
it can be destroyed by the immune system and cleared from the body,
or the bacteria can cause a latent infection that remains dormant. In
this state, the bacteria won't be passed on to someone else, but the
dormant infection can activate months or years later, especially when
the immune system is weakened.
If the initial infection is
not cleared by the immune system and it does not go dormant, it will
move into the airways of the lungs, forming large cavities of air that
become a breeding ground for the infection.
About one in 10 people who are infected with TB eventually develop active
TB. People with a weakened immune system from HIV infection are much
more likely to get an active TB infection.
Symptoms of active TB include coughing, excessive sweating, fatigue,
fever and coughing up blood. It can also result in difficulty breathing.
TB can largely be prevented.
Proper ventilation plays a big role in keeping it from spreading within
a community. Hospitals and clinics may use ultraviolet light to sterilize
the air while special filters, respirators and masks can help prevent
the disease's spread.
Preventative drug therapy can
keep a latent infection from developing into an active infection, and
stifle transmission from infected to uninfected people.
There is one existing TB vaccination
approved for humans, called the Bacille Calmette-Guérin vaccine, but
it only provides partial protection for children and is no help for
adults. It is most often given to infants in countries where TB infection
is high.
TB can be treated successfully
in many cases with a combination of antibiotics taken for at least six
to nine months. But the increasing prevalence of drug-resistant strains
of the bacteria has made battling the disease more complicated. For
every major TB medication available there is now a TB strain that is
resistant to it. Multidrug-resistant TB, or MDR TB, can't be treated
with the two most-powerful TB antibiotics, isoniazid and rifampin. MDR
TB can be treated but requires expensive new drugs and can take up to
two years to treat.
Extensively drug-resistant
TB, or XDR TB, can't be treated with the best first- or second-line
drugs, including those used to treat MDR TB. Patients are left with
treatment options that are less effective and often do not have successful
outcomes.
Sources: Mayo Clinic, National
Institute of Allergy and Infectious Disease, WHO, NIH and CDC
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