Tuberculosis Flashcards
Is the disease burden from TB increasing or decreasing?
It is falling globally
How bad is the TB epidemic?
- TB is the number 1 killer of communicable diseases.
- TB kills more than HIV and Malaria together.
What are the vulnerable groups in the UK for TB?
- Those from high prevalence countries.
- Homeless, alcoholics, IDU’s, those with mental health problems and in prison.
- HIV positive, Immunosuppressed.
- Elderly, neonates, diabetics.
Which mycobacteria can cause TB?
- M. tuberculosis, M. africanum, M. bovis.
- They are non-motile bacillus, very slow growing and aerobic.
- Uniquely has a very thick fatty cell wall.
- HOWEVER, not all acid and alcohol fast bacilli (AAFBs) are TB.
How is TB transmitted?
- Airborne (pulmonary & Laryngeal TB spreads, the others not)
- Usually requires prolonged close contact.
- Outdoors mycobacteria is eliminated by UV radiation and dilution.
What is the exception to the rule about hoe TB is spread?
- Exception is Mycobacterium bovis, which can be spread by consumption of unpasteurized infected cows’ milk (very uncommon in the U.K.)
Immunopathology (immune responses) for TB
Activated macrophages > Epithelioid cells > Langhan’s giant cells
Accumulation of macrophages, epithelioid & Langhan’s cells > GRANULOMA
Central caseating necrosis (may later calcify)
How is the Th1 cell mediated immunological response like a two edged sword?
- It eliminates/ reduces number of invading mycobacteria.
- Tissue destruction is a consequence of activation of macrophages.
Features of primary infection of TB
- No preceding exposure or immunity.
- Mycobacteria spread via lymphatics to draining hilar lymph nodes.
- Usually no symtoms, can be fever, malaise.
What does the primary infection progress to (in a small number 1%)?
It progresses to Tuberculous bronchopneumonia.
- Primary focus continues to enlarge - cavitation
- Enlarged hilar lymph compress bronchi, lobar collapse
- Enlarged lymph node discharges into bronchus
What does the primary infection progress to (in a small number 1-3%)?
- Miliary TB (looked like millet seeds on autopsy) develops, with hematogenous spread of bacteria to multiple organs
- Fine mottling on X-ray, widespread small granulomata
- CNS TB in 10-30%
What does the primary infection progress to (in the majority >85%)?
- Initial lesion + local lymph node (Primary complex)
- Heals with or without scar. May calcify (Ghon focus + complex)
- Associated with development of immunity to tuberculoprotein
What are the two main hypothesis’ of post primary disease?
- TB bacteria entering a dormant stage with low or no replication over prolonged periods of time.
- Balanced state of replication and destruction by immune mechanisms.
What are the clinical presentations of TB?
- Cough
- Fever
- Sweats (mainly at night)
- Weight loss
- All three symptoms
- CRP normal in 15%, ESR normal in 21%.
What may be absent in the clinical presentations of TB?
- Fever absent in 37%
- Sweats absent in 39%
- Weight loss absent in 38%
- All three absent in 25%
