Microbial Disease and epidemiology

Question 1

Koch’s postulates

Answer 1

1. Microbe must always be present in the organism showing the symptoms
2. Microbe must be removed and grown outside the host
3. isolated microbe must be capable of infecting a different host
4. newly infected host must have the microbe isolated again

Question 2

Limitations of the postulates

Answer 2

• Viruses, prions etc cannot be grown in artificial media
• Disease is genetically unstable and changes between host transfers
• pathogenesis depends on host specific characteristic which are not uniform in the population
• lots of possible bacteria

Question 3

Infection epidemiology

Answer 3

• Infection must leave a host via an “exit portal”, be transmitted to a new host by direct or indirect means and infects the new host via an “entrance portal”

Question 4

Infection reservoirs and zoonoses

Answer 4

• Environment where pathogens live and breed

- zoonoses spread to humans via an animal reservoir

Question 5

Determinants of virulence

Answer 5

any mechanism allowing the:

• Colonisation of the hose
• Evasion of immune response
• Spread within/between host(s)