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Tuberculosis:
The Persistent Plague
Tuberculosis
(abbreviated TB) is a highly infectious, sometimes fatal disease
that is caused by the bacteria Mycobacterium tuberculosis. It is
characterized by the formation of hard nodules (tubercles) on lung
or bone tissue. Although it is possible for any organ of the body
to be affected by TB, infection of the lungs is by far the most
common. The disease is contracted by inhalation of respiratory droplets
that have been discharged into the air by an infected person or
animal. However, it is not possible to contract TB by physical contact
such as handshakes, use of toilet seats, or the use of shared dishes
or utensils.
Most
people who become infected with TB do not exhibit any initial symptoms
of the disease. However, the bacteria can lie dormant in the body
for several years, and may become active if the person's immune
system is weakened. Symptoms of active TB disease are cough, sputum,
bleeding from the lungs, night sweats, loss of appetite, weight
loss, and a low-grade fever. If left untreated, the infection can
eventually destroy large areas of the lungs or spread to other areas
of the body such as the kidneys, brain, or spine. Miliary tuberculosis
is an especially dangerous form of TB in which large numbers of
bacteria enter the bloodstream, causing many tiny tubercular lesions
to form, leading to severe anemia and a gradual wasting of the body.
It is almost always fatal unless it is promptly treated.
An
initial diagnosis of TB can be made by administering a tuberculin
skin test. If the test is positive, doctors will usually perform
a chest X-ray and an examination of sputum (phlegm that is coughed
up from the lungs). These will definitively confirm the presence
or absence of TB. If a skin test is negative, a second skin test
may be administered several weeks later. If this is also negative,
the possibility of TB can be effectively ruled out in the vast majority
of cases.
When
a person is diagnosed with TB, the most effective treatment consists
of a four-drug regimen of isoniazid (INH), rifampin, pyrazinamide,
and ethambutol. These medicines must be taken regularly (usually
about 2-3 times per week) for 6 to 12 months, depending on the severity
of the infection, for the treatment to be completely effective.
It is very important that these medications are taken consistently
for the full length of the prescribed time period. When patients
are very inconsistent in taking these medications, or if they stop
taking them once they begin to feel better and do not complete the
full treatment cycle, drug-resistant strains of TB may develop.
These resistant strains are much more difficult to treat, and the
side effects of the additional drugs required for such treatment
are usually much greater than those for the standard treatment.
The fatality rate for drug-resistant TB strains is also much higher.
The
standard antibiotic treatment for TB can also be used as a preventive
measure for people who test positive for latent TB but have not
yet developed the active disease. Thus it is important for people
who believe that they may have been exposed to TB or who are at
a high risk for contracting TB to receive testing. Other preventive
measures include the use of strict standards for ventilation, air
filtration, and isolation methods in hospitals, dental offices,
nursing homes, prisons, or other buildings where TB patients may
be present. There is a vaccine for TB called Bacilli Calmette-Guerin,
or BCG, but it is only effective in about 50% of people who are
vaccinated. This vaccine is very seldom used in the United States
because of its perceived unreliability, but it is frequently administered
to children in other parts of the world where TB is more common.
In the United States, it is hoped that the discovery of the complete
DNA of Mycobacterium tuberculosis in 1998 will lead to the development
of a much more effective vaccine in the near future.
Tuberculosis
has been one of the most common and persistent diseases throughout
human history. Evidence of TB has been found in mummies and skeletons
dating from as early as 2400 BC. The ancient Greeks called TB phthisis,
or "consumption", a term that was commonly used until
the middle of the 20th century. In medieval times, TB was known
as the "white plague" and was widely feared. It was sometimes
confused with leprosy, and for this reason, people who were infected
with TB were often shunned and isolated by most medieval societies.
By the 17th and 18th centuries, many physicians and scientists began
to seriously study TB, and some of them began to conjecture that
the disease might be caused by some type of "minute living
creature".
In
the 1850's, the development of the sanatorium represented the first
major step in controlling the spread of TB. This allowed TB patients
to receive good supportive care under proper sanitary conditions.
Finally, in 1882, Robert Koch managed to develop a staining technique
that enabled people to actually see the Mycobacterium tuberculosis
specimen. This put to rest the persistent myth that "consumption"
could arise spontaneously within an individual person.
Once
the actual bacteria had been identified, the real search for an
effective cure could begin. The first success came in 1943 when
doctors developed an antibiotic called streptomycin. Other important
antibiotics such as isoniazid, ethambutol, and rifampin were developed
in the 1950's and 1960's, and during this period, the incidence
of TB declined rapidly, leading many people to believe that TB had
been effectively eradicated. However, in the mid-1980's, approximately
coinciding with the discovery of the AIDS virus, TB began to resurface.
In the 1990's, renewed efforts aimed at preventing the spread of
both TB and AIDS brought the disease under control again for the
most part, although TB is still a significant problem in many underdeveloped
countries. Today, most of the research in the area of TB treatment
is focused on developing methods of battling persistent drug-resistant
strains of TB.
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