Tuberculosis Flashcards
How many people are affected by TB worldwide?
2 mil - it’s a global problem.
What disease is TB often linked with?
HIV
If you have HIV more likely to get TB and if you have TB will make your HIV worse.
Why was there a flare up of TB during the war time?
Because of overcrowding, social destruction and poor nutrition.
Where is TB the biggest problem in the UK?
39% cases in UK are in London.
Due to really dense populations.
What kind of organisms is responsible for TB?
Mycobacteria.
What are mycobacteria?
There are numerous species, ubiquitous in soil and water.
Few species responsible for human disease.
Non-motile, v. slowly growing (disease slow = treatment long)
Aerobic (predilection for apices of lung)
What mycobacterium are responsible for tuberculosis?
Mycobacterium tuberculosis
What are the mycobacterium other than tuberculosis causing (MOTT)?
Mycobacterium avium-intracellulare (HIV)
M. kanasii, M. malmoense, M. xenopii
Mycobacterium leprae = leprosy.
What is unique about the cell walls of mycobacterium?
Very thick
Composed of lipids, peptidoglycan, arabinomannans.
What does the special cell wall allow the mycobacterium to be?
Resistant to acids, alkalis and detergents.
Resistant to neutrophil and macrophage destruction.
What stain is used to identify mycobacterium?
They’re acid and alcohol bacilli which are stained by the Ziehl Nelson stain.
What are the sources of M. tuberculosis?
Case of ‘open’ pulmonary TB, coughing, sneezing…
Respiratory droplets evaporate.
Drop nuclei containing mycobacterium (1 cough 3,500 nuclei = 5 min speech).
Remain airborne for v. long periods.
Can M. tuberculosis spread outside?
Outdoors mycobacteria eliminated by UV radiation and infinite dilution.
How does the size of the infected droplet affect clearance by the immune system?
If larger droplet nuclei - impacts on large airway and cleared.
If small droplet nuclei (<5microm), 1-3 organisms impact in alveoli and slowly proliferate.
Where can you find M. bovis?
In milk from infected cows.
Where is M. bovis deposited in the body?
Deposited in cervical and intestinal lymph nodes.
Describe the body’s immune response to M. tuberculosis.
APC endocytoses the bacteria and migrates to local lymph nodes and presents antigen to T helper cells. Some T cells recognise this and proliferate. These T cells get back to the macrophage and M. tuberculosis and macrophage becomes activated and can now kill the TB causing bacteria by producing cytokines and free radicals but this causes damage also to healthy tissue.
What occurs as a result of the pro-inflammatory cytokines, chemokines, immune cells and lipid produced by the destruction of M. tuberculosis?
Central caseating necrosis (which may later calcify).
The Th1 cell mediated immunological response is a two edged sword - what is meant by this statement?
Eliminates/reduces no. of invading mycobacteria
vs
Tissue destruction as a consequence of activation of macrophages.
What is the outcome of infection dependent on?
Infection - i.e. virulence and number.
Susceptibility - i.e. genetics, race, nutrition, age, immunosupression.
What differs between a resistant and susceptible host?
Susceptible host - malnutrition, elderly = lots of tissue destruction, organism proliferates = progressive disease.
Resistant host - healthy diet, >20 years = some tissue destruction, organism contained, some disease.
What is a primary infection with TB and who normally gets it? Where does the infection normally focus?
No preceding exposure or immunity.
Usually children.
80% infected focus in alveolus (lymph nodes, gut)
How can mycobacterium spread?
Via lymphatics draining into hillier lymph nodes.
Haematogenous seeding of mycobacteria to all organs of the body (lungs, bone, genitourinary system).
What are the symptoms and signs of primary infection with TB?
Usually no symptoms, can be fever and malaise
Erythema nudism, rarely chest signs
In the majority (85%) -
Initial lesion and local lymph node (primary complex)
Heals with or without scar (may calcify - Ghon focus and complex).
Primary infection is associated with development of immunity to what protein?
Tuberculoprotein.
What test will determine whether you have immunity from primary infection?
Heaf/Tuberculin tests.
Describe the Heaf/Tuberculin test.
Intradermal administration of tuberculoprotein (PPD) results in lymphocytic and macrophage based area of inflammation/induration after 48 hours.
What are the three outcomes of primary infection?
Progressive disease
Contained latent (dormant 1 or 2 bacteria in lung waiting until immunosuppressed, poor diet, older…)
Cleared and cured.
In what percent of people does the primary infection progress? And what does this entail?
1%
Primary focus continues to enlarge - cavitation
Enlarged hilar lymph compress bronchi, lobar collapse
Enlarged lymph node discharges into bronchus
= tuberculous bronchopneumonia
POOR PROGNOSIS
6-12 months after infection what happens to 1% of people after primary infection?
Miliary TB fine mottling on X-ray, widespread small granulomata
Meningeal TB, severe, CSF high protein, lymphocytes
Tuberculosis pleural effusion