Mycobacteria and Tuberculosis Flashcards
TB prevalence?
2nd most infectious killer worldwide
Mycobacterium tuberculosis features?
2-4 μ by 0.2-0.5 μ Obligate aerobe well-aerated upper lobes Facultative intracellular parasite usually macrophages Slow generation time 15-20 h
Where does tuberculosis most commonly affect? Where else can it effect?
Lungs - Pulmonary TB
Lymph nodes, bones, joints, kidneys and can cause meningitis
How do people catch TB?
Droplets from coughs or sneezes
Close/frequent prolonged contact with an infected person
Who is most at risk to TB?
Who else is at risk?
People with weakened immune systems
HIV infec Steroids, chemotherapy, transplants, elderly Unhealthy, overcrowded conditions High rate country - S.E Asia Exposed to TB in youth Prisoners, drug addicts, alcoholics Malnourished
How does primary TB occur?
Droplet nuclei inhaled = taken up by alveolar macrophages - not activated
Droplet nuclei reaches alveoli = infec begins
Granuloma in lung = Ghon focus
Enlarged lymph nodes + GF = primary complex
What causes secondary TB?
Reactivation of dormant mycobacteria - impaired immune func
Reinfec in a person previously sensitised to mycobacterial antigens
- occurs in months, yrs, decades after 1 infec
Where is reactivation of TB most common?
Apex of lungs - highly oxygenated
What occurs in secondary TB?
Caseous centres of tubercles liquefy = organisms grow very rapidly here
Large Ag load:
- Bronchi walls become necrotic and rupture
- Cavity formation
- Organisms spill into airways and spread to other areas of lung
Primary lesions heal - Ghon complex, Simon foci
How do TB infection and TB lung disease differ?
Infec TB: Chest x-ray normal Sputum smears negative putum culture negative No symptoms Not infectious Not defined as a case of TB
Lung disease TB Lesion on chest x-ray Sputum smear positive Sputum culture positive Symptoms Infectious Defined as TB case
What do TB infec and TB lung disease have in common?
Organism present
Tuberculin skin test positive
Most common symptoms of TB?
Cytokines causing: Persistent cough, +/- sputum Anorexia Weight loss Swollen glands Fever Night sweats Sense of tiredness Coughing blood
How to treat TB?
Isoniazid, rifampicin, pyrazinamide and ethambutol
for two months followed by isoniazid and rifampicin for four months
Non-infec after 2 weeks
Begin to feel better after 2-4 weeks
Treatment for 6+ months (prevent resistance)
Longer treatment for TB meningitis or if TB is resistant
How to prevent spread of MDR-TB? (multi-drug resistant)
Standardised drug regimens
Directly observed treatment
Good supply of high quality drugs
Isolation of infectious pts
What does vitamin D do?
Activates macrophages to destroy macrobacteria
