Tuberculosis
(TB) is an infection caused by a germ called
the tubercle bacillus or Mycobacterium tuberculosis.
Until effective anti-tuberculosis drugs
were introduced about 50 years ago, TB was
one of the main causes of death.
TB is still
a major problem in many countries. It has
been on the increase in the developed world
in recent years, probably because of increased
air travel and movement of people from areas
where it is common.
It can affect
the lungs (pulmonary TB) or other parts
of the body, such as the lymph nodes (tuberculous
adenitis or scrofula), the skin and the
bones. Tubercle bacilli can remain dormant
for years before producing active disease.
In most cases
lung infection is well controlled by the
immune system, and shows no symptoms. Active
lung disease occurs if the immune system
becomes less effective.
A person
may have had an infection with tuberculosis
without being aware. This can be discovered
by a tuberculin skin test, the Mantoux test.
When positive, it indicates that the person
has a degree of natural immunity. People
who test negative do not have this immunity
and are more susceptible to infection by
TB.
Tuberculin-negative
people may benefit from BCG inoculation.
This uses a vaccine made from a modified
version of the TB germ. It stimulates natural
immunity, and reduces the risk of developing
TB by about 70 per cent.
Symptoms
Symptoms
of pulmonary TB include fever, fatigue,
loss of appetite and weight, night sweats
and persistent cough. Phlegm coughed up
may be streaked with blood. Tuberculous
pleurisy (affecting the membranes around
the lungs) leads to an accumulation of fluid
in the pleural cavity (the normally very
small space between the membranes) and partial
collapse of the lung.
Rarely,
the TB in the lung erodes an artery, causing
dangerous bleeding into the lung. TB may
then spread widely throughout the body via
the bloodstream (called miliary tuberculosis).
Meningitis is another dangerous complication.
Causes
Pulmonary
tuberculosis is usually caught from someone
by coughing and sneezing tubercle bacilli.
The TB germ has a thick capsule, and can
survive dry and usually hostile conditions.
Historically, spitting phlegm in public
places was banned once it was realised that
the dust from the dried phlegm from someone
who is TB positive could be kicked up and
carry the TB germ into the air, where it
could be inhaled. General (systemic) tuberculosis
is usually caught from infected and unpasteurised
milk from cows with bovine tuberculosis.
Treatment
Tuberculosis
is treated with antituberculous drugs in
combination, for at least 6 months.
Treatment
normally consists of a combination of antibiotics.
The standard treatment involves Isoniazid
and Rifampicin being given for at least
six months. Pyrazinamide is given for the
first two months of treatment and together
with Ethambutol if it is suspected that
a drug-resistant organism is present. Rifabutin,
Cycloserine, Capreomycin and Streptomycin
can also be used in the treatment of TB.
It is vital
to complete the course of drugs as directed.
If this is not done the bacteria will not
be completely eradicated and drug- resistant
strains may develop. Drug-resistant strains
of the bacteria have become an increasing
problem. The last decade has seen the spread
of drug-resistant strains of the TB bacteria.
Some strains are now resistant to the two
leading drugs, Isoniazid and Rifampicin,
and some are multi-drug resistant (MDR).
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Tuberculosis
