Session 6

Question 0

What are the Henle-Koch postulates for?

Answer 0

• To determine if an infectious agent is the cause of a disease

Question 1

What are the Henle-Koch postulates?

Answer 1

• The organism must occur in every case of the disease
• The organism cannot occur in any other disease
• On removal from the body and grow in a pure culture, it can induce the disease anew

Question 2

What are the problems with the first requirement of the Henle-Koch postulates?

Answer 2

(The organism occurs in every case of the disease)

• Definition of the disease (syndrome)
• Difficulties with the isolation of the microbe

Question 3

What are the problems with the second requirement of the Henle-Koch postulates?

Answer 3

(It occurs in no other disease or in health)

• Commensal organisms (naturally occur in humans and have a symbiotic relationship) can be pathogens
• Endogenous infection (caused by an agent already present in the body but has previously been inapparent or dormant)
• Colonisation without symptomatic disease is common

Question 4

What are the problems with the third requirement of the Henle-Koch postulates?

Answer 4

(On removal from the body and grown in pure culture, it can induce the disease anew in a suitable animal model)

• No suitable model
• No pure culture eg viruses

Question 5

What are other problems with the Henle-Koch postulates?

Answer 5

• Lack of control studies

- Many contradictory findings

Question 6

What are endogenous infections?

Answer 6

• Caused by an infectious agent that is already present in the body but has previously been inapparent or dormant

Question 7

What are exogenous infections?

Answer 7

• Caused by a pathogen or agent not normally present in the body

Question 8

How are infectious diseases spread?

Answer 8

• Reservoir ) same in endogenous
• Immediate Source ) infections
• Mode of transmission
• Susceptible host

Question 9

How can infections be reduced?

Answer 9

• Reservoir (1) -> Immediate source (2) -> Mode of transmission -> Susceptible host
• Eliminate microbe from 1 and/or 2
• Remove 3
• Isolate 4 from 2 or protect 4

Question 10

What is Ro?

Answer 10

• The number of secondary infections resulting from one infectious case

Question 11

What does it mean when Ro > 1

Answer 11

• The infection propagates

Question 12

What does it mean when Ro < 1?

Answer 12

• The infection dies out