Tuberculosis Flashcards
Name the species of TB responsible for causing infection in humans
- mycobacterium tuberculosis
- mhycobacterium bovis
Describe the features of mycobacterium
- non-motile bacillus
- slow growing
- aerobic (hence likes lung apices)
- very thick cell wall
- AAFB
- resistant to neutophil and macrophage destruction
How is mycobacterium tuberculosis transmitted
- source = open case of TB
- coughing and sneezing, droplets into air
- remain airborne for long periods
- small droplets reach alveoli and proliferate
- occurs indoors; UV radiation eradicated the bacteria
How is mycobacterium bovis transmitted
- consumption of infected cow’s milk
- deposited in cervial and intestinal lymph nodes
Describe the body’s immune response to infection with TB
- pathogen recognised
- engulfed by antigen presenting cells
- clonal proliferation of Th1 cells
- activate macrophages to engulf the pathogen
- activated macrophages cause tissue damage
- granuloma form from gatherings of macrophages and giant cells
- causes central caseating necrosis (gatherings of dead TB cells)
Describe the features of a primary infection of TB
- no preceding exposure or immunity
- usually children
- spread to hilar lymph nodes, then to all organs
- usually no systemic symptoms
- often malaise, fever, erythema nodosum
- majority heals with a scar and may later calcify
Describe the basis of the Heaf/Mantoux tuberculin tests
- tuberculoprotein administered under the skin
- inflammation indicates positive result
- indicates previous exposure to TB
What are the three outcomes of a primary infection if TB
- progressive disease (1%)
- contained latent infection (switch to susceptible host)
- cleared and cured infection (majority)
Explain the process of progressive disease after primary infection with TB
- primary focus continues to enlarge
- cavitation may occur
- enlarged hilar nodes compress and collapse bronchi/lobe
- node discharges into bronchus giving tuberculous bronchopneumonia
What is miliary TB
- a form of TB that occurs months after a primary infection
- fine mottling on CXR
- widespread, small granuloma
What is meningeal TB
- a form of TB that occurs months after a primary infection
- severe
- high protein in CSF
- high levels of lymphocytes
Describe how post primary disease of TB arises
- reactivation of bacteria from primary latent infection
- spreads in blood all over the body
or - new re-infection from outside the body
- can spread to any other tissue in the body
- different host response expected due to previous sensitisation
What are the main clinical symptoms of post primary infection of TB
- cough
- sputum
- haemoptysis
- pleuritic pain
- dyspnoea
- malaise
- fever
- night sweats
- weight loss
What aspects of the clinical history may indicate infection with TB
- diabetes
- immunosuppression (drugs/HIV etc)
- alcohol abuse (poor nutrition)
- IVDA
- poor social circumstances
- immigrants from high incidence areas
What tests can be performed in sputum to help diagnose TB
- culture (may take up to 8 weeks)
- PCR
- smear (ZN stain for AAFB)
