Principles Of Infection

Question 1

What is a commensal?

Answer 1

A microbe that lives in us without doing any harm

Question 2

What is Normal flora?

Answer 2

A microorganism that lives on another organism without causing disease

Question 3

What is a parasite?

Answer 3

An organism that can damage us

Question 4

What is colonisation done by?

Answer 4

Commensal organisms

Question 5

What is asymptomatic carriage?

Answer 5

When an organism is colonised by a pathogen but not actually causing any harm (that we can see)

Question 6

What is an infection?

Answer 6

When the pathogen is actually causing harm

Question 7

What is a saprophyte?

Answer 7

Free living organism

Question 8

What are parasites dependant on?

Answer 8

Their hosts

Question 9

What is an opportunist?

Answer 9

Organisms that are normally Commensals, but become pathogens and cause disease, mainly due to the host being immunocompromised

Question 10

What is a conditional pathogen?

Answer 10

A pathogen that depends on preexposure

Question 11

What is a full pathogen?

Answer 11

Initiates infection via natural route despite immune defences

Question 12

What does infection imply?

Answer 12

Harm is done to the host, caused by the pathogen

Question 13

When can Commensals become pathogens (3)?

Answer 13

• found in another site
• immunocompromised
• bypassing defences (eg getting bitten)

Question 14

What is a pathogen?

Answer 14

Microbe that can initiate infection, often with only small numbers, via natural routes despite natural barriers and immune defences

Question 15

Name some sites (in the body) that don’t have a normal flora

Answer 15

• Lower respiratory tract
• blood
• bone, joint and subcutaneous connective tissue
• female upper genital tract
• urinary tract
• CNS including CSF and eyes
• other viscera, like liver, spleen and pancreas

Question 16

What are highly pathogenic microbes called?

Answer 16

Virulent

Question 17

What is virulence?

Answer 17

The degree to which the pathogen causes disease

Question 18

According to kochs postulates, what does a microorganism have to do to show that the pathogen causes that disease (4)?

Answer 18

• be present in every case of infection
• be cultured from cases in vitro
• reproduce disease in an animal
• be isolated from the infected animal

Question 19

Do kochs postulates still hold up today (and if not, what differences are there)?

Answer 19

Mainly, although we now know not all organisms can be cultured, but you can detect their genomes by PCR and its not universally applicable to all diseases

Question 20

What are the three types of infection?

Answer 20

Local, invasive and systemic

Question 21

What is a local infection?

Answer 21

Surface infection in a wound

Question 22

What is an invasive infection?

Answer 22

It can penetrate barriers and lead to a local spread

Question 23

What is a systemic infection?

Answer 23

When the infection moves via blood to other sites

Question 24

What is inflammation?

Answer 24

Response to tissue injury functions to bring serum molecules and cells to the site of infection

Question 25

What are the 4 features of acute infection?

Answer 25

- rapid onset - major local and systemic symptoms - acute inflammatory response - toxin mediated

Question 26

What are the 3 features of chronic infection?

Answer 26

- Slower onset or post- acute - may still have major local and systemic symptoms - chronic inflammatory response

Question 27

When does chronic infection happen?

Answer 27

when host doesnt succumb immediately to infection, but cannot clear it either

Question 28

What are the three features of asymptomatic infection?

Answer 28

- infection with a pathogenic microbe - inflammatory response and damage to the host is mild or nonexistent - no symptoms present

Question 29

What does ‘reactivation from latent infection’ mean?

Answer 29

You have cleared the disease once, but the pathogen remains latent in the body, and then its reactivated later when you may be immunocompromised

Question 30

Do all microbes need to go through all stages of infection?

Answer 30

No

Question 31

What are the 7 stages of infection?

Answer 31

- acquisition from spread (9Fs) - colonisation (adherence) - penetration and spread - tissue damage - shedding and transmission - resolution

Question 32

What are the 9Fs?

Answer 32

``` Fingers Fresh air Fomites Fluids Faeces Flies Food Foetus Fornication ```

Question 33

What does fomites mean?

Answer 33

Things we share like door handles or toys

Question 34

Where are the three places mucosal contact can happen?

Answer 34

Genital tract, saliva and skin

Question 35

What do virulence factors promote?

Answer 35

Colonisation and adhesion and tissue damage

Question 36

What is adherence?

Answer 36

Surface adhesion structures of bacteria and viruses

Question 37

What is the muco-cillary clearance mechanism?

Answer 37

When the pathogen releases cytotoxins which specifically damages the cilli and then they can attach