Tb Flashcards
How is TB transmitted?
Human-Human
Characteristics of TB
Acid-Fast Aerobic Bacili
Can TB be stained using gram stain technique?
No. Waxy lipid outer wall prevents effective staining
What is the function of waxy lipid wall
protects Mtb from disinfectants, allowing them to survive within macrophages for long time
who is at risk of TB
intense exposure
old
young
hiv
immunocompromised
how is tb spread
inhalation of droplet nuclei; aerosolised by coughing, sneezing, talking
what type of tb is:
a) more infectious
b) less infectious
a) sputum AFB smear positive
b) sputum AFB smear neg, culture positive
describe the pathogenesis of tb
- airborne droplet nuclei of MTB reaches terminal airspaces in the lung
- Multiplication of MTB
- Initial pulmonary focus (usually single focus)
- Bacterial ingested by alveolar macrophages; macrophages destroyed by bacterial multiplication
- Attracts lymphocytes and more macrophages to the site
- Causes pneumonitis and/or lymphohematogenous dissemination to regional lymph nodes or extra-pulmonary organs
- immune system controls infection - granuloma formation
- if small antigen load + high tissue hypersensitivity: well formed granuloma, containment of infection healing with eventual fibrosis, encapsualtion and scar formation
- If high antigen load +high tissue hypersensitivity: poor organisation of immune cells leading to incomplete necrosis = caseating granuloma;; liquefying and discharge thru bronchial tree, producing tb cavity with high numbers of MTB. infectious material sloughed from a cavity creates new exudative foci in pther parts of the lung (bronchogenic spread)
what are the possibilities of progression of TB
- Non-progressive, containment by encapsulation - latent TB
- Miliary TB: disseminated hematogenous tb; can lead to TB meningitis in young
- Subpleural primary focus may rupture, causing pleural effusion
- Seeding to apical-posterior areas of lung, where disease may progress without interruption or after a latnet period, resulting in pulmonary TB of the adult or re-activation of TB
- Large hilar or mediastinal lymph nodes = bronchial collapse (infection erodes into a bronchus and spreads distally = causes cavities)
How can one develop active TB from latnet TB
recent infection due to close contact of a perosn with TB
infancy, 15-25 years old, old age
no longer able to contain latent infection due to immunosuppression
- HIV infection
- immunocompromised states (bone marrow transplant, on immunosuppressants, poorly controlled DM)
How to test for LBTI?
TST & IGRA
Symptoms of active TB
Fever
Night Sweats
Weight Loss (due to TNF)
Chronic Cough
Hemoptysis
Lymphadenopathy
Malaise
Anorexia
Physical Exam results for Active TB
Lymphadenopathy
Percussion Dullness
Crackles on auscultation
Whispered pectoriloquy (consolidation)
Blood tests for Active TB
Normocytic Normochromic Anemia
WCC normal
Hyponatremia (due to adrenal TB or SIADH)
Sterile pyuria in renal TB
CSF in TB meningitis (refer to the chart)
radiographs of active TB
refer to slides
