Principles of Infection 2

Question 1

Steps to becoming unwell with an infection

Answer 1

1. Transmission
2. Infection
3. Pathogenicity
4. Virulence

Question 2

what happens at the transmission step?

Answer 2

host has to acquire the organism

Question 3

what happens at the infection step?

Answer 3

the organism has to reproduce inside the host

Question 4

what happens at the pathogenicity step?

Answer 4

organism interacts with the host in a way that causes diseases

Question 5

what happens at the virulence stage?

Answer 5

organism causes a disease of varying severity

Question 6

example of air-borne spread

Answer 6

aerosols or droplets from cough etc

Question 7

examples of person to person spread

Answer 7

direct e.g. skin infection, STDs

Question 8

Examples of faceo-oral spread

Answer 8

most often via food/ water e.g. cholera

Question 9

examples of consumption of infected material transmission

Answer 9

e.g. salmonella, tapeworm

Question 10

example of vector-borne disease transmission

Answer 10

mosquitos spread malaria & zika infection

Question 11

example of endogenous infection transmission

Answer 11

from movement of own microbiome e.g. colonic bacteria to urine

Question 12

example of direct inoculation transmission

Answer 12

e.g. open fracture, bite form infected animal

Question 13

how do microorganisms cause disease?

Answer 13

indirect damage by host immune response and direct damage by the pathogen

Question 14

How does the host immune response cause indirect damage?

Answer 14

• inflammation causes tissue damage & lost of normal function
• systemic response to infection can cause organ failure and death

Question 15

How does a pathogen cause direct damage?

Answer 15

• viral reproduction causes cell lysis ( cell breakdown)
• Bacteria secrete toxins causing cell damage

Question 16

How do microorganisms evade the immune system?

Answer 16

1. Adhere (stick) to the epithelium
2. Invade epithelial cells / cross epithelial barrier
3. Evade innate immune cells
4. Evade adaptive immune cells and antibodies

Question 17

define virulence factors:

Answer 17

components or structure of microorganisms that helps in establishment of disease or infection (essentially to assist microorganism to colonise)

Question 18

virulence factors include factors that allow microorganisms to:

Answer 18

• Adhere to and invade host tissues
• Evade host defences
• Proliferate in the host
• Cause damage
• Produce toxins
• host- pathogen interaction

Question 19

tiny hairs on bacteria are called?

Answer 19

pili

Question 20

Define adhesins

Answer 20

(on bacteria that) allows them to stick onto epithelial cells & stops them from being swept away

Question 21

Define adhesins and pili

Answer 21

pili- tiny hairs (on bacteria that) and adhesins allow them to stick onto epithelial cells & stops them from being swept away

Question 22

Some bacteria secrete enzymes which do what?

Answer 22

degrade the host molecules by attacking the epithelial barrier (e.g. breaking down tight junctions)

Question 23

secretion of enzymes allows bacteria/ viruses to?

Answer 23

get past the barrier and then sit in the interstitial/ extracellular fluid however can get into epithelial cells or immune cells (e.g. tuberculosis)

Question 24

Once bacteria/virus has invaded the cell, they will do what?

Answer 24

set of signalling molecules that will propagate this and make this process worse

Question 25

Steps to adherence and invasion

Answer 25

- Bacteria has anatomical structure (pili and adhesins) - Some bacteria secrete enzymes, attacking the barrier - Can however get into epithelial or immune cells - once invaded it will set of signalling molecules

Question 26

Examples of evade host defences in bacteria

Answer 26

capsule, cell wall and toxins

Question 27

Examples of evade host defences in viruses

Answer 27

antigenic drift, antigenic shift

Question 28

Function of capsule in bacteria

Answer 28

-protects bacteria from host immune response and antibiotics

Question 29

'frustrated phagocytosis' enhances?

Answer 29

the inflammatory response

Question 30

define frustrated phagocytosis

Answer 30

occurs when phagocytic cells are exposed to an opsonised surface and spread as if trying to engulf it

Question 31

Function of cell wall in bacteria

Answer 31

- contains endotoxins - excreted after cell death & lysis - Activate a pathway of events weakening host (septic shock)

Question 32

define antigenic drift

Answer 32

small changes in viral antigens due to point mutations in genes

Question 33

define antigenic shift

Answer 33

Major changes in vial antigens due to gene reassortment

Question 34

virulence factors are determined how?

Answer 34

genetically

Question 35

Horizontal gene transfer enables?

Answer 35

bacteria to respond and adapt to their environment rapidly by acquiring large DNA sequences from another bacterium in a single transfer

Question 36

Horizontal gene transfer therefore means bacteria can?

Answer 36

share antibiotic resistance genes

Question 37

genes disseminated by horizontal transfer allows?

Answer 37

bacteria to share common pathogenic mechanisms and antibiotics resistance

Question 38

Strep A is transmitted how?

Answer 38

person- person spread, air- borne

Question 39

Infection by Streptococcus A is what type of bacteria? shape? oxygen conditions?

Answer 39

Gram positive Cocci shape Aerobe

Question 40

Pharyngitis also known as

Answer 40

sore throat

Question 41

scarlet fever also known as?

Answer 41

rash

Question 42

How does sore throat (pharyngitis) cause indirect damage by host immune response?

Answer 42

Bacteria invade throat cells - immune system fights bacteria causing inflammation

Question 43

How does scarlet fever cause direct damage by the pathogen?

Answer 43

Bacteria in the throat make a toxin that enters the body and causes a skin rash

Question 44

How does Invasive group A strep disease by direct damage by the pathogen?

Answer 44

Bacteria evade the immune system and spread to a normally sterile body site- toxin causes shock and multiorgan failure

Question 45

Virulence of sore throat, rash, Strep A?

Answer 45

Sore throat: mild- very common Rash: moderate - less common Strep A : severe - very rare

Question 46

what causes influenza?

Answer 46

viruses: several types cause infection in humans : influenza A, B & C

Question 47

How is Influenza highly transmissible?

Answer 47

air- borne, person to person direct & indirect contact, can also come from animals and birds

Question 48

How does Influenza infect?

Answer 48

viruses enter cells of respiratory tract and proliferate

Question 49

Pathogenesis of Influenza via direct damage

Answer 49

-Viruses directly damage respiratory cells by lysis during reproduction

Question 50

Pathogenesis of Influenza via indirect damage

Answer 50

-Viruses cause indirect damage by triggering an immune response which causes damage and symptoms

Question 51

Viiruses make a lot of 'mistakes' during replication, by creating?

Answer 51

new strains

Question 52

SARS- CoV-2 is what type of virus

Answer 52

RNA virus

Question 53

Why do RNA viruses have a high mutation rate?

Answer 53

RNA viruses dont have proof reading mechanisms to correct mistakes

Question 54

define a variant

Answer 54

where the viral genome contains one or more mutations

Question 55

List ways some variants confer advantages on the virus

Answer 55

- Increase transmissibility