Haematogenous spread

Question 1

What is haematogeous spread?

Answer 1

Spread of pathogens through bloodstream

Question 2

How do pathogens enter blood-stream?

Answer 2

Catheters- these are fomites

Surgery- causes a wound

Meningitis- bacteria break through lining of nose & throat to entry blood

UTI- bacteria can travel from bladder to kidneys- produce tissue damaging toxins- can access the bloodstream

Pneumonia - the bacteria infects the epithelium cells in the alveoli, causing them to die. This breaks the barrier btw the alveoli & the blood. Also releases a toxin ExoS to help do this.

Question 3

How do pathogens survive & spread in the host? How does innate immune response struggle?

Answer 3

Stress survival
- Host defences may damage the pathogen by denaturing proteins.
- Chaperonins (heat shock proteins) protect against denaturing of other proteins.
- Free radicals e.g. hydroxyl radicals & hydrogen peroxide damage & kill pathogens.
- may be produced by the pathogen’s aerobic metabolism, or by host defences.

Scavenge for nutrients
- Some nutrients, sugars, amino acids & fatty acids are freely available, but Fe 3+ is not.
- Fe 3+ is important for bacterial survival & its inaccessibility is part of innate defence provided by the body.
- Fungi acquire nutrients from dead or decaying organic matter.

Shelter
- If the pathogen can enter host cells it will be protected from antibody attack.
- All viruses replicate w/in host cells, & some bacteria, fungi & protozoa shelter w/in cells.
- When bacteria or virions are released from cell they are fully exposed to the immune system, but viruses or bacteria that pass directly from one cell to another minimise this exposure.

Antigenic variation
- Some pathogens mutate & change their antigens.
- can happen during an infection of an individual, or it may happen between outbreaks, such as influenza, so that the pathogen remains one step ahead.

Question 4

Complication of infection?

Answer 4

Sepsis
- Overreaction of the immune system in response to a systemic infection, where it releases too many cytokines, causing multi-organ failure.
- Can also happen in response to certain toxins that act as super antigens, causing T cells to release more cytokines.

Toxin production
- Diphtheria, which stops protein synthesis.
- Staphylococcal food poisoning (enterotoxin B),leads to severe diarrhoea and nausea.

Immunodeficiency
- HIV destroys its host T cells, which can make the patient immunocompromised.