1. Introduction

Question 1

What are the names of the three types of associations between one organism with its host?

Answer 1

1. Parasitic
2. Symbiotic
3. Commensalism

Question 2

What is a parasitic association?

Answer 2

Where one organisms benefits at the expense of the other.

Question 3

What is a symbiotic relationship?

Answer 3

Where both organisms associated benefit.

Question 4

What is a commensal relationship?

Answer 4

Where one organisms benefits while causing no harm to the other.

Question 5

Give examples of symbiotic relationships in vertabrates with their microorganisms.

Answer 5

1. The microflora inhabiting the rumen of cows breaking down cellulose to provide the cow with its nutrition.
2. Bacteria inhabiting the human intestinal tract that supply vitamins

Question 6

What is horizontal transmission of disease?

Answer 6

One individual infecting another by contact.

Question 7

What is vertical transmission of disease?

Answer 7

One individual affecting offspring via sperm, ovum, the placenta, milk or by contact.

Question 8

How would you describe a “successful” microbe?

Answer 8

One that lives in or on an individual host, is able to multiply and spread to fresh individuals in order to maintain itself in nature.

Question 9

How would you describe a “successful” parasitic microbe?

Answer 9

One that gets what it needs from the host without causing too much damage which may interfere with its ability to maintain itself in nature.

Question 10

How would you describe a “successful” parasitic microbe?

Answer 10

One that gets what it needs from the host without causing too much damage which may interfere with its ability to maintain itself in nature.

Question 11

What are the 7 obligatory steps for infectious microorganisms?

Answer 11

1. Attachment and entry into the body
2. Local or general spread in the body
3. Multiplication
4. Evasion of host defences
5. Shedding (exit) from the body
6. Cause damage to the host not strictly necessary

Question 12

What are the 7 obligatory steps for infectious microorganisms?

Answer 12

1. Attachment and entry into the body
2. Local or general spread in the body
3. Multiplication
4. Evasion of host defences
5. Shedding (exit) from the body
6. Cause damage to the host not strictly necessary

Question 13

What disease was introduced into the rabbit population in 1950 and how may this be an example of a successful microbe?

Answer 13

Myxomatosis was introduced into rabbits in 1950 killing 99% of the population, however it soon evolved into a less pathogenic state, allowing for increased lifespan of infected rabbits, death of fewer rabbits and thus prevention of the further depletion of the host species.

Question 14

What disease was introduced into the rabbit population in 1950 and how may this be an example of a successful microbe?

Answer 14

Myxomatosis was introduced into rabbits in 1950 killing 99% of the population, however it soon evolved into a less pathogenic state, allowing for increased lifespan of infected rabbits, death of fewer rabbits and thus prevention of the further depletion of the host species.

Question 15

If balances pathogenicity if the ideal microbe state, why do diseases still exist which are so detrimental to the host?

Answer 15

1. Many infections have not yet had time to reach this ideal state.
2. The human host is irrelevant for the survival of the organism and its maintainance in nature

Question 16

If balances pathogenicity if the ideal microbe state, why do diseases still exist which are so detrimental to the host?

Answer 16

1. Many infections have not yet had time to reach this ideal state.
2. The human host is irrelevant for the survival of the organism and its maintenance in nature

Question 17

What are the 4 conditions of Kock’s postulates which must be met in order to link a pathogen to a disease?

Answer 17

1. All people with the disease should be infected with the suspected pathogen but healthy individuals should not be.
2. The pathogen must be isolated in pure culture from the site of infection.
3. The cultured micro-organism must cause the disease when introduced into a healthy organism.
4. The micro-organisms must be re-isolated from the experimental host and identified as the same organism isolated from the first host.

Question 18

What are the 4 conditions of Kock’s postulates which must be met in order to link a pathogen to a disease?

Answer 18

1. All people with the disease should be infected with the suspected pathogen but healthy individuals should not be.
2. The pathogen must be isolated in pure culture from the site of infection.
3. The cultured micro-organism must cause the disease when introduced into a healthy organism.
4. The micro-organisms must be re-isolated from the experimental host and identified as the same organism isolated from the first host.

Question 19

What are the 4 conditions of Kock’s postulates which must be met in order to link a pathogen to a disease?

Answer 19

1. All people with the disease should be infected with the suspected pathogen but healthy individuals should not be.
2. The pathogen must be isolated in pure culture from the site of infection.
3. The cultured micro-organism must cause the disease when introduced into a healthy organism.
4. The micro-organisms must be re-isolated from the experimental host and identified as the same organism isolated from the first host.

Question 20

Why has it proved difficult to fulfil Koch’s postulate for many pathogens? (6 points to mention)

Answer 20

1. Inability to obtain a pure culture.
2. Passage in the laboratory leads to the loss of pathogenic properties (attenuation)
3. Some diseases are caused by a combination of more than one micro-organism.
4. Different strains of the same species can have different pathogenic properties.
5. Variation in host susceptibility
6. Lack of suitable animal model or human volunteers for experimentation.

Question 21

Why has it proved difficult to fulfil Koch’s postulate for many pathogens? (6 points to mention)

Answer 21

1. Inability to obtain a pure culture - i.e prions in CJD
2. Passage in the laboratory leads to the loss of pathogenic properties (attenuation)
3. Some diseases are caused by a combination of more than one micro-organism.
4. Different strains of the same species can have different pathogenic properties.
5. Variation in host susceptibility
6. Lack of suitable animal model or human volunteers for experimentation.

Question 22

Why was Koch’s first postulate (the pathogen must be found in diseased individuals but not healthy individuals) abandoned?

Answer 22

This was done so to explain carrier’s of particular diseases.
Koch isolated the pathogen of cholera and later typhoid fever in asymptomatic individuals

Question 23

Why is Koch’s second postulate (that the cultured pathogen will cause disease when reintroduced into a new host) also problematic?

Answer 23

Disproving the first postulate shows that not all infected individuals will show symptoms.

Question 24

Why is Koch’s second postulate (that the cultured pathogen will cause disease when reintroduced into a new host) also problematic?

Answer 24

Disproving the first postulate shows that not all infected individuals will show symptoms.

Question 25

What is “signature tagged mutagenesis”?

Answer 25

STM is a genetic technique used to study gene function by disabling the gene and observing the effect on the organism in order to infer the gene function.

Question 26

How is STM important in the study of pathogenesis?

Answer 26

To identify the pathogen genes associated with the virulence factors important in its pathogenicity. .

Question 27

What is the basic premise of STM?

Answer 27

Insertion of a transposon into the gene in question causing the production of a defective and non-functional protein. If a change in phenotype is observed, the genome can be sequences to search for ‘tags’ of the transposon which should be within a gene and thus the gene affected can be identified.

Question 28

Give an example of the use of STM in the study of pathogenesis?

Answer 28

A random array of mutated pathogens are inserted into a host to observe which of the mutants survive. Those that did not survive have a mutation in a gene important for pathogenesis and therefore these genes can be identified.