Host pathogen interactions

Question 1

What are the three domains of the phylogenetic tree of life?

Answer 1

Bacteria, Archaea, Eukaryota

+ viruses, virusoids, prions

Question 2

Pathogenicity

Answer 2

the ability to cause disease

Question 3

Virulence

Answer 3

the measure of pathogenicity

Question 4

The ‘Iceberg’ concept of infectious diseases: M.tuberculosis

Answer 4

-disease in about 10% of those infected

Question 5

Asymptomatic infection

Answer 5

individual infects others, seroconverts, resists infection

Question 6

Chain of events of transmissable infections:

Answer 6

1. Transmission

2, Entry - mucosal surfaces (resp. tract, gastro. tract, genitourinary tract) or skin (wound, insect bite)

Question 7

Chain of events of transmissable infections:

3. Attachment and colonisation

Answer 7

• competition with normal flora
• specific adhesion mechanisms to host receptors
• evade and survive barriers (eg. stomach acid)
• localised infection (establishment phase, followed by dissemination)
• generalised/systemic infection or toxin spread from a localised site

Question 8

Chain of events of transmissable infections:

4. Multiplication in vivo

Answer 8

• appropriate conditions (nutrients, pH, temp., aerobic/anaerobic)
• exceptions -food poisoning/diptheria

Question 9

Chain of events of transmissable infections:

5. Evasion of host defence mechanisms

Answer 9

• Innate (non specific)
• Adaptive (specific) immune mechanisms
• manipulation of host immunity

Question 10

Chain of events of transmissable infections:

6. Damage to host

Answer 10

i. Direct damage by infectious agent
- -> Multiplication within and destruction of host cells
- -> Exotoxins

ii. Indirect damage via inflammation
- -> overactivity can damage the host’s own tissues (endotoxin -fever,shock,hypotension)

iii. Indirect damage via immune response
- -> Overactivity (hypersensitivity) can cause tissue damage (immunopathology)

Question 11

Damage to host can be caused by …

Answer 11

-pathogen itself
and/or
-by host’s own defence reactions

Question 12

Whether or not disease occurs depends on many factors….

Answer 12

• pathogenic potential
• susceptibility of host
• way in which they encounter
• species
• genetics (selection of ancestors)
• age
• gender
• nutritional status
• immune status

Question 13

The ‘Hygiene hypothesis’

Answer 13

• asthma and allergic conditions
• antibiotics
• non re-colonisation after antibiotics