8.1 - mycobacterium tuberculosis Flashcards
mycobacterium tuberculosis
acid fast bacterium
major pathogenic species within mycobacterium
tuberculosis strains
§ MDR-TB - multi drug resistant TB
§ XDR-TB - extensively drug resistant TB
TB acquired by
§ Disease of overcrowding and poor social conditions
§ Usually acquired by inhalation from another person with active pulmonary TB
§ Bacteria may persist in the air in the room for some time
TB aerosol particles
□ Aerosol particles
□ 0.5 to 5 micrometres
□ Size gives these particles the ability to be inspired directly to the level of the alveoli without being filtered out at higher levels of the airways
§ Infection may be acquired by inhaling as few as ten tubercle bacilli
bodily spreads of TB
§ In the alveoli mycobacteria are ingested by alveolar macrophages
□ They able to survive and multiply within macrophages
□ Innate immune system, cannot control the infection, but adaptive immune system can control but not eradicate the infection in the lung
infectivity of TB
§ Majority of people who become infected with M tuberculosis remain asymptomatic
§ About 20% of people with develop symptoms, 10% within 2 years (1° TB) and 10% some years later (2° TB) as a result of reactivation of latent TB
location of TB
§ TB is typically a pulmonary disease but 10-25% of cases are extrapulmonary
§ Ghon focus
□ Granulomatous inflammation
® 1-1.5cm in diameter
® Mid lung, unilateral
® Becomes fibrosed and walled off, later calcifies
® Majority of infected patients remain asymptomatic with viable bacteria walled off in fibrotic tubercles in lung or other tissues
hon focus may develop into
ghon complex
Ghon complex
when ghon focus progresses to involve peribronchial and hilar lymph nodes
primary TB
◊ In 10% of infected people the Ghon complex will progress and the infection disseminates through the lungs
} Tuberculosis pneumonia
} Patchy or dense consolidation
} Cavitation
◊ Primary TB usually seen in infants and children
if the goon complex progresses and disseminates through the lungs this is
primary TB
second degree TB happens when
◊ If cell mediated immunity diminishes then lesions may reactivate and patient becomes symptomatic
second degree TB happens in which people
} Old age } Steroids } Diabetes } Immunosuppressive drugs } HIV infection
why do many people remain asymptomatic
Majority of infected patients remain asymptomatic with viable bacteria walled off
clinical features of TB
□ Gradual, non-specific onset □ Fever □ Night sweats □ Tiredness □ Weight loss □ Persistent cough with possible blood stained sputum
in untreated TB
□ Progressive involvement of the lungs may occur , resulting in cavity formation and scarring usually involving the upper lobes
□ Untreated pulmonary tuberculosis is highly infectious, particularly where there is a cavitating lesion opening into an airway
4 methods of detecting TB
Mantoux
interferon gamma release assay
chest X ray
sputum testing
Mantoux involves
□ Mantoux (tuberculin) skin test
® This involves the intradermal injection of a bleb purified preparation of M tuberculosis antigen (PPD - purified protein derivative)
positive Mantoux test
® People who have been infected with MTB will develop a local skin reaction which is measured after 48 hours
problem with Mantoux test
◊ A positive test does not differentiate between latent infection and active infection
□ Interferon gamma release assay
® This test detects interferon gamma release from the patient’s T lymphocytes after being incubated, in vitro, with M tuberculosis synthetic peptides
positive IFN gamma release assay
® T lymphocytes previously exposed to the organism will release high levels of interferon gamma
problem with IFN gamma release assay
® A positive test dies not differentiate between latent infection and active infection
