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Title: Tuberculosis
Description: These are notes on tuberculosis taught in a clinical microbiology module in the third year of a biomedical science degree course. The notes cover the pathogenesis, clinical features, diagnosis, treatment, and prevention of tuberculosis.
Description: These are notes on tuberculosis taught in a clinical microbiology module in the third year of a biomedical science degree course. The notes cover the pathogenesis, clinical features, diagnosis, treatment, and prevention of tuberculosis.
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Tuberculosis
Tuberculosis is one of the most serious infectious diseases of the resource-poor world
...
TB affects the apparently healthy as well as being a serious disease of the
immunocompromised and is one of the AIDS-defining illnesses
...
infection is acquired by inhalation of M
...
Airborne
transmission of TB is efficient because infected people cough up enormous numbers of TB
mycobacteria, projecting them into the environment, where their waxy outer coat allows them
to withstand drying and therefore survive for long periods of time in air and house dust
...
Non-resident macrophages are attracted to the site, ingest the
mycobacteria and carry them via the lymphatics to the local hilar lymph nodes
...
Some M
...
Sensitized T cells release lymphokines that
activate macrophages and increase their ability to destroy the mycobacteria
...
The lung lesion plus the enlarged lymph nodes is called the
Ghon or primary complex
...
The tubercles may heal spontaneously, become
fibrotic or calcified, and persist as such for a lifetime in people who are otherwise healthy
...
Secondary TB is
due to reactivation of dormant mycobacteria and is usually a consequence of impaiered
immune function resulting from some other cause such as malnutrition, infection eg
...
TB illustrates the dual role of the immune response in infectious
disease
...
However, all the pathology and disease is a consequence of the
immune response, as M
...
Reactivation occurs most commonly in the apex of the lungs, as this site is more highly
oxygenated than other sites, thus allowing the mycobacteria to multiply more rapidly to
produce caseous necrotic lesions, which infect other sites in the lung, from where organisms
can spread to more distant sites in the body
...
Primary TB is usually mild and asymptomatic, with the majority
of cases failing to proceed further
...
Mycobacteria have the ability to colonize almost any site in the body
...
Lung infection characteristically causes a chronic productive cough and the sputum may be
blood stained as a result of tissue destruction
...
The organism may disseminate via the
lymphatics and bloodstream to other parts of the body, in this way chronic foci are
established, which may proceed to necrosis and destruction in, for example, the kidney
...
Diagnosis
The cell mediated, T-cell response can be detected by the tuberculin skin test, also called
the Mantoux test, 4-6 weeks after infection by injecting a small amount of purified protein
derivative of M
...
A positive result is shown by local induration and erythema, 48-72 hours
later
...
A strong skin test reaction would lead to referral to a
respiratory clinic for further assessment and treatment
...
A diagnosis of TB is suggested by the clinical signs
and symptoms, supported by characteristic changes on chest radiography and positive skin
test reactivity in the tuberculin test
...
tuberculosis
...
This
result can be obtained within 1 hour of receipt of the specimen in the laboratory
...
tuberculosis can take up to 6 weeks to grow in culture, although
radiometric methods may reduce the time required for detection, and therefore confirmation
of the diagnosis is necessarily delayed
...
tuberculosis are
PCR and the automated Xpert MTB-RIF molecular test that detects TB and rifampicin
resistance
...
Treatment
Mycobacteria are innately resistant to most antibacterial antigens, and specific
anti-tuberculosis drugs have to be used
...
Treatment also includes prolonged therapy, for a minimum
of 6 months, which is necessary to eradicate these slow growing intracellular organisms
...
Other factors include variable
quality of the drugs and poor prescribing practices
...
Multidrug-resistant TB occurs when there is
little response to the first line drugs, isoniazid and rifampicin
...
Prevention
Improvement in social conditions and in the prevention of TB
...
Immunization with a live attenuated bacille calmette-Guerin vaccine has been
used effectively in situations where TB is prevalent
...
In areas where there is a low prevalence of disease,
immunization has been largely replaced by chemoprophylaxis
...
Title: Tuberculosis
Description: These are notes on tuberculosis taught in a clinical microbiology module in the third year of a biomedical science degree course. The notes cover the pathogenesis, clinical features, diagnosis, treatment, and prevention of tuberculosis.
Description: These are notes on tuberculosis taught in a clinical microbiology module in the third year of a biomedical science degree course. The notes cover the pathogenesis, clinical features, diagnosis, treatment, and prevention of tuberculosis.