Quick checks
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Check your understanding
Which link is most direct for influenza?
- Respiratory epithelial damage can impair mucociliary defence.
- Loss of helper T cells is its principal stated tissue effect.
- Persistence inside macrophages creates latent TB infection.
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Respiratory epithelial damage can impair mucociliary defence.
Damage to those cells reduces an important protective function.
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Which is the principal transmission route described for pulmonary TB?
- Ingestion of contaminated drinking water
- Inhalation of infectious airborne particles
- Ordinary skin contact with a person who has latent infection
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Inhalation of infectious airborne particles
This route can deliver bacteria to the lungs.
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Which explains penicillin's bacterial selectivity?
- It inhibits cellulose cross-linking in bacterial walls.
- Its wall-synthesis target is present in susceptible bacteria but absent from human cells.
- It digests the existing peptidoglycan of every bacterium, whether growing or not.
- It attacks a structure shared equally by human and bacterial cells.
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Its wall-synthesis target is present in susceptible bacteria but absent from human cells.
Target differences provide selective toxicity.
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Which is NOT a reason penicillin is selectively toxic to bacteria?
- Human cells have no transpeptidase
- Penicillin cannot enter human cells at all
- Human cells have no peptidoglycan wall
- Only bacteria build cross-linked walls
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Penicillin cannot enter human cells at all
Selectivity comes from the target: transpeptidase and peptidoglycan exist only in bacteria. Entry into human cells is not the reason.
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Which best explains indirect protection?
- Reduced transmission gives susceptible people fewer infectious encounters.
- Milder symptoms alone protect neighbours even if transmission is unchanged.
- Protection requires every person in the population to be individually immune.
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Reduced transmission gives susceptible people fewer infectious encounters.
The chain is interrupted through population-level effects.
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Which statement about a pandemic is correct?
- It describes extensive international spread of an epidemic.
- It begins whenever R0 exceeds 1, regardless of geographical spread.
- It must always have a higher fatality rate than every local outbreak.
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It describes extensive international spread of an epidemic.
The category concerns the distribution of transmission.
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In a simple model, a disease has R0 = 5. What proportion of the population must be immune to stop its spread?
- 100%
- 50%
- 80%
- 20%
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80%
The threshold is 1 - 1/R0 = 1 - 1/5 = 0.8, or 80%.
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