Tuberculosis

Question 1

describe tuberculosis

Answer 1

caused by myobacterium tuberculosis bacterium

currently a global epidemic

Question 2

describe M. tuberculosis

Answer 2

rod shaped bacillus
gram postive 
acid fast characteristics
slow growing member of genus 
myo-bacterium due to fungal like growth on solid media

Question 3

describe TB infection

Answer 3

transmission is via aerosol route
exposure to TB-infected individuals results in infection in ~10% cases
vaccine not very effective - the RD1 genomic segment of M. TB is absent from all strains of BCG vaccine
most common in 25-34 year olds
majority of TB disease is re-activated disease in individuals previously entering the country with latent TB infection

Question 4

describe elimination of TB

Answer 4

identify and effectively treat accurate TB
identify and treat people with latent TB infection at risk of progression to accurate TB

left untreated, the disease will progress to eventually involve most of the lung bilaterally (milairy TB)

Question 5

describe symptoms of TB

Answer 5

constitutional

organ specific - pulmonary, extra-pulmonary (spinal cord, brain)

Question 6

describe signs of TB

Answer 6

generalised

organ specific - pulmonary, extra-pulmonary (spinal cord, brain)

Question 7

describe how the host’s immune response largely shapes the clinical outcome of TB

Answer 7

*as list progresses, more effective immune response (time also affects the disease)*
miliary
meningeal
pulmonary (widespread)
pulmonary (localised)
localised extra-pulmonary 
lymph node
healthy contact (latent TB infection)

Question 8

describe the diagnosis of TB

Answer 8

history and examination
simple blood test
radiology/imaging
microbiology and histology;
specimens - sputum, gastric washings, bronchoalveolar lavage, early morning urine, biopsies
procedures - microscopy (Ziehl-Neelsen and Auramine)
culture - solid and liquid phase, drug sensitivities
histology - granuloma with central caseous necrosis (cheesy)

Question 9

describe treatment of drug-sensitive TB

Answer 9

active;
4 drugs for 2 months; rifampicin, isoniazid, pyrazinamide, ethambutol
2 drugs for further 4 months; rifampicin, isoniazid

latent;
2 drugs for 3 months; rifampicin, isoniazid
or 1 drug for 6 months; isoniazid

Question 10

describe the immune response to M. TB

Answer 10

the macrophage is the initial intracellular primary niche of M. TB

1. phagocytosis (macrophage, dendritic cell, neutrophil)
2. immune recognition and innate effector mechanisms (anti-mycobacterial effector functions)
3. (slow) onset of Th1-biased adaptive immunity (MTB-specific CD4+ T cell and CD8+). This is key to successful anti-TB immune response. Individuals with defective CMI (HIV or chronic renal failure) are not defective humoral immunity and exhibit markedly increased risk of TB
4. enhanced effector mechanisms (more effective immune response)

Question 11

describe diagnosis of latent TB infection

Answer 11

ESAT-6 and CFP-10 are potent targets of IFN-gamma secreting T cells in TB

Question 12

describe diagnosis of active TB

Answer 12

sensitivity of 3 samples

may be sensitive as a culture