Tuberculosis Flashcards
Tuberculosis?
An infectious disease caused by Mycobacterium tuberculosis
Explain the bacterium.
- It is a rod-shaped, aerobic bacterium
- resistant to destruction and persist in necrotic and calcified lesions for prolonged periods and remain capable of reinstating growth
Mode of transmission?
Airborne infection spread by droplet nuclei (coughing; sneezing; talking)
What increases the risk of developing TB?
Overcrowded living conditions
Why is cell-mediated response important?
It is important in walling off the tubercle bacilli and preventing the development of active TB
What happens if your cell immunity is impaired?
You are more likely to develop active TB
What does a positive TB test indicate?
You are infected but it doesn’t mean you have active TB
How many cases of TB occur in Canada each year and how many deaths?
1600; 130deaths
In Canada, who is it more common in?
Foreign borne persons and Canadian-borne persons in northern Canada
List the microbes that are responsible.
Mycobacterium, M. Tuberculosis
Explain the structure.
- slender, rod-shaped aerobic bacterium that do not form spores.
- Have outer waxy capsule
What does the outer waxy capsule do for the bacterium?
It makes them more resistant to destruction
Why is infection most frequently in the lungs?
The tubercle bacilli are strict aerobes that thrive in an oxygen rich environment. The lungs have the greatest concentration of O2 and ventilation.
What is the patho of TB centered on?
The development of a cell-mediated IR that gives resistance to the organism and development of tissue hypersensitivity to the tubercular antigens.
What do the destructive features on the disease result from?
Hypersensitivity IR rather than the destructive capabilities of the tubercle bacillus
What are the primary cells that are infected by M. TB?
Macrophages
Where does the inhaled droplet nuclei deposit? Briefly explain
Inhaled droplet nuclei pass down the bronchial tree without settling on the epithelium and are deposited on the alveoli
What happens once the inhaled droplet nuclei is deposited on the alveoli?
Bacilli are phagocytised by alveolar macrophages but resist killing because cell wall lipids of M. TB blocks fusion of phagosomes and lysosomes
Whys is the initial attack by macrophages incapable of destroying the bacillus?
The cell wall lipids of M. TB block fusion of phagosomes and lysosomes
How is it ultimately destroyed?
Macrophages initiate a cell-mediated IR that eventually contains the infection. As tubercle bacilli multiply, infected macrophages degrade the mycobacterium and present their antigens to T-lymphocytes. Sensitized T-lymphocytse stimulate macrophages to increase concentration of lytic enzymes and ability to kill mycobacteria.
Ghon focus?
- Grey- white, granulomatous lesion
- contains the tubercle bacilli, modified macrophages, and other immune cells
- located in sub pleural area of the upper segments of the lower lobes or lower segments of the upper lobe
Ghon complex?
- combination of the primary lung lesion and lymph node granulomas
- eventually heals, undergoing shrinkage, fibrous scarring, and calcification
Latent TB?
- T-lymphocytes and macrophages surround the organism in granulomas that limit their spread
- W/ this, you do not have active disease and cannot transmit the organism to others
What can latent TB develop into?
Secondary TB
