L2 How Pathogens Cause Disease

Question 1

What do microbes need for them to survive?

Answer 1

• Suitable habitat
• Exploit habitat for nutrients
• Disperse to new suitable habitat if necessary

Question 2

How do we act as humans act as a habitat for them?

Answer 2

• Produce virulent factors into us
• Elicit immune response
• Cause damage in humans
• Nutrients provided to them (e.g. via inflammation = many nutrients in one site)

Question 3

Why cause disease?

Answer 3

• Conflict of interests affect bacterial species (e.g. nutrients and space)
• Different organisms evolved different strategies to maximise chances of survival
• For pathogens to survive - need large pool of susceptible individuals and high rate of transmission

Question 4

Virulence gene postulates

Answer 4

• Gene encoding trait of interest should be present in a virulent strain
• Gene encoding trait of interest should not be present in strain that doesn’t cause disease
• Disruption of gene in virulent strain should result in formation of strain that is incapable of causing disease
• Introduction of gene into strain that previously did not cause disease should transform strain into one that does cause disease

Question 5

Issues with Koch’s postulates

Answer 5

Need to be able to grow in lab but some can’t grow within lab e.g. Leprosy
Ethical issues - don’t want to inject anyone with HIV

Question 6

What are the stages within ‘Cycle of Infection’?

Answer 6

1. Encounter
2. Entry
3. Spread
4. Evade defences
5. Multiply and damage
6. Disperse

Question 7

Endogenous infections within Encounter stage

Answer 7

Infection from organism already inside the body (commensal microbiota get into the wrong place)
e.g. oral streptococci -> endocarditis (derived from organisms in own mouth)

Question 8

Exogenous infections within Encounter stage

Answer 8

Infection from organisms not already in the body

normally via respiratory/ faecal-oral/ venereal/ inanimate or animal vectors

Question 9

Routes of transmission

Answer 9

Horizontal = From person to person
Vertical = From mother to child

Question 10

Entry methods

Answer 10

Ingress
Penetration
Adhesion

Question 11

Ingress

Answer 11

Pathogen entering existing cavity of the body e.g. inhale pathogen into lungs via standard route

Question 12

Penetration

Answer 12

Damage to site allows pathogen to enter (also via surgery)

• Cholera - secretes toxin causing efflux of ions and water
• Bacterial dysentery -
• Typhoid fever - penetrate into tissue and enter bloodstream to disintegrate through body

Question 13

Adhesion

Answer 13

Needs to stick to surface before it causes infection via recognising cell receptors (determining tropism)

Question 14

Spread and evade

Answer 14

e. g. Streptococcus progenies
- capsule
- leukocidins
- degradation of host tissue and other barriers

Question 15

Damage

Answer 15

Food-borne illnesses
AB toxins
Immunopathogenesis

Question 16

Factors increasing susceptibility

Answer 16

• Age
• Sex bias
• Hobbies
• Immune system and age
• Nutrition
• Overcrowding
• Violent exercise