Section 3

Question 1

What has changed from the 1900’s to now in regards to deaths?

Answer 1

• Decreased deaths from infectious diseases

- Increased deaths from heart disease & cancer

Question 2

Is the immune system 100% protective?

Answer 2

No, because diseases still exist

Question 3

What is the difference in the generations times of bacteria and host cells?

Answer 3

Average generation for bacteria is 1 hour, while for host cells it is 20 years

Question 4

What are 2 characteristics that microbes posses to overcome host defenses?

Answer 4

• Evolution

- Gene exchange on plasmids/transposons

Question 5

What kind of competition is going on once a pathogen enters a host?

Answer 5

Whether or not the number of microbes can be kept below the threshold level

Question 6

What does a delayed immune response mean?

Answer 6

Disease and shedding

Question 7

Why is there a higher prevalence of disease in the winter?

Answer 7

Because people stay inside and are much closer to other people, therefore increasing the chance of coming in contact with an infected individual

Question 8

What does a pathogen need to do once they enter the body?

Answer 8

Adapt and change

Question 9

Define disease threshold

Answer 9

The level that a microbe must reach to produce a disease

Question 10

If someone has a pathogen that is below threshold, can they spread to other people?

Answer 10

Yes, not being in the disease state does not mean that they are not infectious

Question 11

What is needed for a beneficial host-pathogen relationship?

Answer 11

Adaptation of both pathogen and host without extensive damage

Question 12

What are the causes of microbial infections that can occur when antimicrobial defences are intact?

Answer 12

• Microbial attachment/penetration
• Biting arthropod
• Skin wound/animal bite

Question 13

What are the steps of infection?

Answer 13

1) Attachment and possible entry into the body
2) Local or general spread in body
3) Multiplication
4) Evasion of host defences
5) Shedding from body
6) Damage to host

Question 14

Do pathogens always damage the host?

Answer 14

No, but some damage usually occurs during shedding

Question 15

Why did Koch create his postulates?

Answer 15

To determine what microorganism caused a certain disease

Question 16

What are Koch’s postulates?

Answer 16

1) Suspected germ must be present in every case of the disease
2) Must be able to isolate and culture it
3) Must be able to inject pure culture into a healthy individual and cause disease
4) Must be able to isolate suspected germ from newly infected individual

Question 17

What are some challenges associated with Koch’s postulates?

Answer 17

• Unculturable organisms
• Host immunologic factors
• Involvement of more than one pathogen
• Infections only in humans

Question 18

What are the new criteria for Koch’s postulates?

Answer 18

1) Suspected germ should be associated with pathogenic strains much more than non-pathogenic strains
2) Inactivation of genes should decrease pathogenicity
3) Replacement of mutated gene should fully restore pathogenicity
4) Gene should be expressed during infection and disease
5) Antibodies against the gene should protect the host

Question 19

What are factors that influence the severity of an infection?

Answer 19

• Dose and route of infection
• Age
• Sex
• Nutritional status
• Genetic background

Question 20

What is an example of an uncultarable organism?

Answer 20

Treponema pallidum pallidum

Question 21

What is an example of a disease caused by host immunologic factors?

Answer 21

Rheumatoid arthritis

Question 22

What is an example of a pathogen that involves more than one microbe?

Answer 22

HDV

Question 23

What is an example of a pathogen found only in humans?

Answer 23

HIV