Pathogenic mechanisms

Question 1

Diarrhoea

Answer 1

an increase in the frequency, fluidity, volume and water content of faeces.

Can vary in severity, characteristics (bloody/mucoid) according to cause

Question 2

Role of diarrhoea

Answer 2

• Can be a host attempt to remove infection, stop build-up og pathogen or its toxins
• May aid dissemination of disease
• May be a product of mucosal damage
• Can be a result of stress e.g. shipping disease
  
  • Stress hormones in the gut can affect bacteria and lead to overgrowth and/or expression of virulence determinants

Question 3

What are the mechanisms by which pathogens cause diarrhoea?

Answer 3

• Hypersecretion
• Villous atrophy
• Infiltrative and proliferative distortion of mucosa
• Mucosal necrosis

Question 4

Describe how hypersecretion leads to diarrhoea

Answer 4

• Functional disturbance of epithelial cells leads to outflow or decreased reabsorption of water
• This could be by altering the chloride secretion into the crypt space
• e.g. ETEC: enterotoxigenic E. Coli.

Question 5

Describe chloride secretion into the crypt space

Answer 5

• Relevant for how hypersecretion leads to diarrhoea

1. Crypt cells pump Cl- ions into the crypt space
2. These Cl- ions attract Na+ ions into the crypt space, increasing the local osmotic pressure
3. As the osmotic pressure increases, water is ulled into the intestine.

Some enterotoxins can trigger and lock on the chloride secretion, leading to hypersecretory diarrhoea.