Transmission Routes

Question 1

What is virulence?

Answer 1

Virulence is non-scalar (relative). It is a quantitative measure of the extent of disease.

Question 2

How can virulence be measured?

Answer 2

• Amount of fever caused
• Weightloss
• Morbidity
• Mortality

Question 3

How can pathogens adapt to new environments?

Answer 3

By acquiring new mutations

Question 4

How can genetic variability be increased?

Answer 4

• Random mutation and selection

- Horizontal gene transfer

Question 5

Random mutation is what type of process?

Answer 5

A slow process

Question 6

Horizontal gene transfer is what type of process?

Answer 6

A fast process

Question 7

What are the different methods of bacterial horizontal gene transfer?

Answer 7

• Transformation
• Transduction
• Conjugation

Question 8

What is bacterial transformation?

Answer 8

Taking up genetic material from the external environment

Question 9

What is bacterial transduction and what can it occur between?

Answer 9

Transfer of genetic material by phages

Can only occur between closely related bacteria

Question 10

Bacterial conjugation is mediated by?

Answer 10

Pili

Question 11

Bacterial conjugation can occur between?

Answer 11

Distantly related bacteria

Question 12

Direct transmission is associated with what virulence?

Answer 12

Low virulence

Question 13

Why do directly transmitted viruses become less virulent overtime?

Answer 13

Due to the transmission-mortality tradeoff

Question 14

Examples of direct transmission and lower virulence?

Answer 14

Bacterial and viral STDs
Influenza pandemics
Myxoma virus

Question 15

Myxoma virus was released when and where?

Answer 15

Southern Australia 1950s

Question 16

Myxoma virus fatality rate over time?

Answer 16

Initial fatality rate of 99%
Reduced to 50%
Rabbit population gradually recovered overtime

Question 17

Bacterial STD?

Answer 17

Chlamydia

Question 18

Waterborne transmission is associated with what type of virulence?

Answer 18

Associated with increased virulence

Question 19

Why can waterborne diseases be more virulent?

Answer 19

They do not rely on host motility to be spread

Question 20

How can enteric diseases be spread?

Answer 20

• Direct contact, human to human
• Fecal oral
• Waterborne

Question 21

Cholera spreads via?

Answer 21

Fecal oral route

Waterborne

Question 22

Cholera infectious dose?

Answer 22

10^6

Question 23

Why is the infectious dose of cholera so high?

Answer 23

Not very resistant to the stomach acid

Question 24

How much diarrhoea is produced by an infected individual?

Answer 24

Up to 20L of rice water stool a day

Question 25

Rice water stool contains how many pathogens?

Answer 25

10^7 bacteria per ml

Question 26

How does vibrio cholerae obtain mutations?

Answer 26

Horizontal gene transfer and random mutation

Question 27

How does cholera ensure horizontal gene transfer?

Answer 27

Via the T6SS and competence, transformation

Question 28

In the aquatic environment where can cholera be found?

Answer 28

On the exoskeleton molt of zooplankton. The exoskeleton is rich in chitin

Question 29

On the chitinous surface the bacteria forms a?

Answer 29

Biofilm

Question 30

What does the chitinous surface trigger?

Answer 30

It triggers the developmental programme of natural competence for genetic transformation

Question 31

What initiates the developmental programme of natural competence?

Answer 31

TfoX regulatory protein

Question 32

What is TfoX?

Answer 32

It is a regulatory protein

Question 33

Competence is required for?

Answer 33

Transformation

Question 34

What increases the availability of external DNA?

Answer 34

T6SS

Question 35

T6SS does what?

Answer 35

Injects effectors into other bacterial cells which mediates cell lysis etc...

Question 36

T6SS activation is controlled by the?

Answer 36

The T6SS is part of the competence regulon which is initiated by the TfoX

Question 37

What is the colonisation factor of cholera?

Answer 37

TCP

Question 38

What is TCP?

Answer 38

Toxin co-regulated protein | A hair like projection on the surface of the bacterial cell

Question 39

What is the hair like protein on the surface of the bacterial cell>

Answer 39

TCP | Toxin Co-regulated Protein

Question 40

What is the role of TCP?

Answer 40

It is a receptor of the CTX phage It is the colonisation factor for small intestine colonisation It is the colonisation factor required for colonisation of planktonic exoskeletons

Question 41

What carbon source does aquatic cholera use?

Answer 41

Chitin

Question 42

Cholera colonises the?

Answer 42

Small intestine

Question 43

Is cholera internal or external?

Answer 43

Non-invasive and external

Question 44

CTX toxin is encoded by the?

Answer 44

CTX phage

Question 45

CTX toxin structure?

Answer 45

AB5

Question 46

CTX toxin binds to which receptor?

Answer 46

GM1 ganglioside receptor

Question 47

When was the most recent plague outbreak?

Answer 47

Malaysia 2017

Question 48

What types of plague are there?

Answer 48

Bubonic Pneumonic Septicemic

Question 49

All types of plague are caused by?

Answer 49

Yersinia pestis

Question 50

Bubonic plague is spread by?

Answer 50

Arthropod fleas

Question 51

The fleas transmit the bacteria from?

Answer 51

Rats to humans

Question 52

Yersinia pestis evolved from?

Answer 52

Gut pathogen Yersinia pseudotuberculosis

Question 53

When did Yersinia pestis evolve from Yersinia pseudotuberculosis?

Answer 53

1,500 to 20,000 years ago

Question 54

Yersinia pseudotuberculosis is spread via?

Answer 54

The fecal oral route

Question 55

Is Yersinia pseudotuberculosis very virulent?

Answer 55

No

Question 56

Yersinia pseudotuberculosis is a bacterium of the?

Answer 56

Gut

Question 57

In order for Yersinia pestis to have evolved from Yersinia pseudotuberculosis?

Answer 57

It needed to acquire various mutations

Question 58

What allowed survival of Yersinia pestis in fleas?

Answer 58

pFra plasmid

Question 59

How does the pFra plasmid allow survival in fleas?

Answer 59

Yersinia murine toxin

Question 60

What does Yersinia murine toxin allow?

Answer 60

Survival in the flea midgut, resistance to antibacterial agents in the flea midgut

Question 61

What allows Yersinia pestis to form a biofilm in the flea?

Answer 61

hma gene

Question 62

Biofilm prevents the flea from?

Answer 62

Taking meals up, leads to regurgitation, the fleas starve and bite more frequently

Question 63

What encodes the T3SS in Yersinia pestis?

Answer 63

pYv plasmid

Question 64

Which plasmid encodes the T3SS?

Answer 64

pYv plasmid

Question 65

Which plasmid encodes Yersinia murine toxin?

Answer 65

pFra

Question 66

Which plasmid allows dissemination from the bite site, to the lymph nodes etc...?

Answer 66

pPst

Question 67

What does pPst encode?

Answer 67

Pla plasminogen activator

Question 68

Plasminogen activator allows the bacteria to do what?

Answer 68

Infect macrophages and reach the lymph nodes

Question 69

Which plasmids were acquired by Yersinia pestis?

Answer 69

pPst pFra pYv

Question 70

pYv plasmid encodes?

Answer 70

T3SS

Question 71

pFra plasmid encodes?

Answer 71

Yersinia murine toxin

Question 72

pPst plasmid encodes?

Answer 72

Pla plasminogen activator

Question 73

Why is Yersinia pestis so virulent?

Answer 73

1- Poor vector competence... need high bacteremia to infect the vector 2- Host seeking behaviour of the vector: Vector tends to stay on the host. Inducing death in the host causes the vector to move 3- Humans are not the natural host of the disease, no co-evolution over time 4- Vector density, lots of fleas present on the host so even if the host dies there is a high likelihood of transmission

Question 74

What bacteria causes anthrax?

Answer 74

Bacillus anthracis

Question 75

Spore germination occurs?

Answer 75

Within macrophages

Question 76

Where do spores form?

Answer 76

In the environment

Question 77

Why might incidence with anthrax increase?

Answer 77

Due to global warming and thawing

Question 78

What causes death by anthrax?

Answer 78

The toxins produced

Question 79

The virulence factors are encoded on?

Answer 79

Two plasmids

Question 80

What are the two plasmids of anthrax?

Answer 80

pXO1 | pXO2

Question 81

pXO2 produces?

Answer 81

Capsule proteins Forms a protective coat Inhibits phagocytosis

Question 82

PXO1 produces?

Answer 82

The exotoxins

Question 83

What are the exotoxins?

Answer 83

Edema and lethal toxin

Question 84

What does edema toxin do?

Answer 84

Causes large swellings of pus and blood to form

Question 85

What does lethal toxin do?

Answer 85

Leads to host death

Question 86

How do the two exotoxins facilitate spread of anthrax?

Answer 86

The edema toxin causes infected large swellings of pus and blood to form. The lethal toxin causes septic shock and results in death. The edemas rupture to release the bacteria into the environment.

Question 87

The two exotoxins are encoded by?

Answer 87

pXO1

Question 88

What contributes to the high virulence of anthrax?

Answer 88

Environmentally transmitted by sit and wait transmission. This increases its virulence as it does not need to rely on the host motility for transmission. Relies on the motility of the uninfected and its ability to form spores in the environment.