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Chapter 19

Tuberculosis

QuestionAnswer
What type of people get tuberculosis and were is it prevalent? It affects healthy and immunocompromised and is prevalent where poverty and malnutrition is present.
How is infection acquired? By inhalation of mycobacterium tuberculosis in aerosols and dust
Why is this airborne transmission efficient? Infected people cough up enormous numbers of mycobacteria. They have a waxy coat that can withstand drying and survive in the air and house dust
What happens during primary infection? Bacteria is engulfed by the alveolar macrophages. Non-resident macrophages are attracted to the site, ingest the bacteria and carry via lymphatics to the local lymph nodes
What happens in the lymph nodes? A cell mediated immune response is stimulated, which is detectable 4-6 weeks after infection
Is an antibody-mediated immune response also helpful? No, because MTB is intracellular and the high lipid concentration of the cell wall makes it resistant to complement killing
How does the body react to this immune response? It reacts by trying to contain the MTB within tubercles
What are tubercles? Small granulomas consisting of epitheloid and giant cells. The center has ceseation necrosis.
What is Ghon or primary complex? The lung lesions combined with the enlarged lymph nodes.
What happens in dormant/latent MTB infection The tubercles may heal spontaneously, become fibrotic or calcified, and persist for long period of time.
What causes secondary tuberculosis? Re-activation of dormant bacteria as a consequence of impaired immune function suach as malnutrition, infection, chemotherapy or corticosteroids.
Where does re-activation most often occur and why? The apex of the lung is well oxygenated, which allows the bacteria to produce caseous necrotic lesions, which spill over into other sites in the lung and can spread to distant sites in the body.
So, why is this same immune response bad? Nearly all the pathology and disease is a consequence of this CMI response, as MTB causes little or no direct effect or toxin-mediated damage
Where do mycobacteria colonize and how? Mycobacteria colonize almost any site in the body. They may disseminate via the lymphatics and bloodstream to other parts of the body. They may spread by extension to a neighboring part of the lung
How can tuberculosis be prevented? Tuberculosis can be prevented by imporived social conditions, immunization and chemo-prophylaxis.
Why is it so challenging to treat mycobacteria infections? They have a waxy outer layer that makes them impermeable, they are intracellular surrounded by caseous material adn they grow and multiply really slow
What are the two mechanisms currently used to target mycobacteria Some compounds inhibit or target mycolic acid synthesis and one compound inhibits the polymerization of arabinoglycan (a constituent of the cell wall)
Created by: Beantha
 

 



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