Weeks 6-7 Flashcards
What is the main mode of TB resistance transmission?
Primary resistance
What are the 3 dimensions of TB disease?
Macroscopic pathology
Infectiousness
Symptoms
Is CXR superior to a symptom screen?
Yes
What percentage of all prevalent TB is subclinical?
50%
What percentage of subclinical TB is smear positive?
33%
What is subclinical TB?
Macroscopic pathology without symptoms
How is M tuberculosis hominis spread?
Inhalation of infected drops
Conjunctiva
Abraded skin
How long is M tuberculosis hominis viable?
Dry sputum - weeks
Wet sputum - months
How is M tuberculosis bovis transmitted?
Milk from infected cows (eradicated by pasteurisation)
What are symptoms of M tuberculosis bovis infection?
Intestinal lesions
Tonsillar lesions
What are the 5 factors of TB pathogenesis?
- Virulence of bacillus
- Induced hypersensitivity
- Host immunity
- Granulomatous reaction patten
- Intracellular bacillus survival
What is the virulence of the TB bacillus directly related to?
Lipid fractions within the cell wall
What is responsible for tissue destruction in TB?
Hypersensitivity to bacillus
Sensitisation 2-4w post infection
On 1st exposure, non-specific neutrophilic inflammatory response
What does the inflammatory reaction become post sensitisation?
Granulomatous
What does a granuloma consist of?
Epitheloid histiocytes
Langhan’s multinucleated giant cells
Plump fibroblasts
Lymphocytes
How does TB avoid phagocytosis?
Acidification of phagosome via H+-ATPase exclusion
Recruitment of TACO protein prevents delivery to lysosome
How does the presence of iron modify cytokine activity?
Decreased TNF secretion
Decreased IL-1 and IL-6 mRNA
Which protein inhibits macrophage apoptosis in TB?
Mcl-1
What are the mechanisms of TB to inhibit phagosome-lysosome fusion?
Secretion of serine/theanine protein kinase G
Glycoprotein phagosome composition alteration
What is primary TB?
TB infection in previously unexposed individual
In which stage of TB is Ghon focus found?
Primary TB
Where is Ghon focus found?
Area of greatest volume of inspired air
- Lower part of upper lobe
- Upper part of lower lobe
What is a Ghon complex?
Ghon focus + lymph node involvement
When does Ghon focus caseate?
End of 2nd week
What are the outcomes of primary tuberculosis?
- Fibrosis and calcification
- Progressive pulmonary TB
- Transbronchial spread
- Lymphatic spread
- Haemotogenous spread (miliary TB)
What causes post-primary tuberculosis?
Reactivation of latent endogenous infection OR exogenous reinfection
What is the pathogenetic mechanism for post-primary TB?
Bronchial obstruction -> lipid pneumonia -> massive necrosis and cystic cavitation
What areas does post-primary TB usually affect?
Apical and posterior segments of upper lobe (Simon’s foci)
Superior segment of lower lobe
What are the features of post-primary TB?
Apical or posterior segments of one or both upper lobes
Airway obstruction causing lobular lipid pneumonia
Intrapulmonary spread via bronchi
Thin-walled cystic cavitation
1-3cm areas of caseous consolidation 1-2cm beneath pleura
Abundant AFBs
Aerosol formation
Remain localised or progress slowly
What are the outcomes of post-primary TB?
- Fibrocalcific arrested TB
- Progressive pulmonary TB
- Pleural effusions, empyema, pleurisy
- Endobronchial and endotracheal TB
- Intestinal TB
- Lymphatic and blood spread with resultant miliary TB
Erosion of which vessels causes TB limited to the lung vs disseminated TB?
Pulmonary artery -> limited to lung
Pulmonary vein -> systemic dissemination
Name rare sites for TB
Heart
Thyroid
Pancreas
Striated muscle
What is the difference in tuberculomas in children vs adults?
Location
Adults - supratentorial
Children - posterior fossa
Why is TB endometritis difficult to diagnose?
Granulomata are shed every menses
Describe the progress of renal tuberculosis
Lesions in kidney cortex bilaterally -> progress in 1 kidney and stationary in the other -> invades pyramids and calyx walls -> large cavitating mass with shell of normal kidney remaining
How is the performance of LF-LAM as HIV severity increases?
More severe HIV, better performance
Which PLHIV should get an LF-LAM?
Anyone seriously ill admitted to hospital
Any symptomatic patient
Any patient with CD4<200
What are the advantages of TB culture?
Highly sensitive
Low limit of detection
What are the disadvantages of TB culture?
TTP
Requires infrastructure
Why must you be careful with a TB NAAT trace result?
Detection of MTB DNA at lowest limit of detection - can occur in previously diagnosed/treated
What are the advantages of TB Xpert Ultra?
Improved sensitivity
Large PCR reaction volume
Multitarget genetic markers
Which specimens are recommend for Xpert Ultra in children?
Stool
What are the common resistance genes seen with rifampicin?
rpoB
What are the common resistance genes seen with INH?
katG
inhA
What are the common resistance genes seen with bedaquiline?
atpE (ATP synthetase)
rv0678 (efflux pump)
Which culture type yields faster DST results?
Liquid culture