Transmission Routes Flashcards
What is virulence?
Virulence is non-scalar (relative). It is a quantitative measure of the extent of disease.
How can virulence be measured?
- Amount of fever caused
- Weightloss
- Morbidity
- Mortality
How can pathogens adapt to new environments?
By acquiring new mutations
How can genetic variability be increased?
- Random mutation and selection
- Horizontal gene transfer
Random mutation is what type of process?
A slow process
Horizontal gene transfer is what type of process?
A fast process
What are the different methods of bacterial horizontal gene transfer?
- Transformation
- Transduction
- Conjugation
What is bacterial transformation?
Taking up genetic material from the external environment
What is bacterial transduction and what can it occur between?
Transfer of genetic material by phages
Can only occur between closely related bacteria
Bacterial conjugation is mediated by?
Pili
Bacterial conjugation can occur between?
Distantly related bacteria
Direct transmission is associated with what virulence?
Low virulence
Why do directly transmitted viruses become less virulent overtime?
Due to the transmission-mortality tradeoff
Examples of direct transmission and lower virulence?
Bacterial and viral STDs
Influenza pandemics
Myxoma virus
Myxoma virus was released when and where?
Southern Australia 1950s
Myxoma virus fatality rate over time?
Initial fatality rate of 99%
Reduced to 50%
Rabbit population gradually recovered overtime
Bacterial STD?
Chlamydia
Waterborne transmission is associated with what type of virulence?
Associated with increased virulence
Why can waterborne diseases be more virulent?
They do not rely on host motility to be spread
How can enteric diseases be spread?
- Direct contact, human to human
- Fecal oral
- Waterborne
Cholera spreads via?
Fecal oral route
Waterborne
Cholera infectious dose?
10^6
Why is the infectious dose of cholera so high?
Not very resistant to the stomach acid
How much diarrhoea is produced by an infected individual?
Up to 20L of rice water stool a day
Rice water stool contains how many pathogens?
10^7 bacteria per ml
How does vibrio cholerae obtain mutations?
Horizontal gene transfer and random mutation
How does cholera ensure horizontal gene transfer?
Via the T6SS and competence, transformation
In the aquatic environment where can cholera be found?
On the exoskeleton molt of zooplankton. The exoskeleton is rich in chitin
On the chitinous surface the bacteria forms a?
Biofilm
What does the chitinous surface trigger?
It triggers the developmental programme of natural competence for genetic transformation
What initiates the developmental programme of natural competence?
TfoX regulatory protein
What is TfoX?
It is a regulatory protein
Competence is required for?
Transformation
What increases the availability of external DNA?
T6SS
T6SS does what?
Injects effectors into other bacterial cells which mediates cell lysis etc…
T6SS activation is controlled by the?
The T6SS is part of the competence regulon which is initiated by the TfoX
What is the colonisation factor of cholera?
TCP
What is TCP?
Toxin co-regulated protein
A hair like projection on the surface of the bacterial cell
What is the hair like protein on the surface of the bacterial cell>
TCP
Toxin Co-regulated Protein
What is the role of TCP?
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
What carbon source does aquatic cholera use?
Chitin
Cholera colonises the?
Small intestine
Is cholera internal or external?
Non-invasive and external
CTX toxin is encoded by the?
CTX phage
CTX toxin structure?
AB5
CTX toxin binds to which receptor?
GM1 ganglioside receptor
When was the most recent plague outbreak?
Malaysia 2017
What types of plague are there?
Bubonic
Pneumonic
Septicemic
All types of plague are caused by?
Yersinia pestis
Bubonic plague is spread by?
Arthropod fleas
The fleas transmit the bacteria from?
Rats to humans
Yersinia pestis evolved from?
Gut pathogen Yersinia pseudotuberculosis
When did Yersinia pestis evolve from Yersinia pseudotuberculosis?
1,500 to 20,000 years ago
Yersinia pseudotuberculosis is spread via?
The fecal oral route
Is Yersinia pseudotuberculosis very virulent?
No
Yersinia pseudotuberculosis is a bacterium of the?
Gut
In order for Yersinia pestis to have evolved from Yersinia pseudotuberculosis?
It needed to acquire various mutations
What allowed survival of Yersinia pestis in fleas?
pFra plasmid
How does the pFra plasmid allow survival in fleas?
Yersinia murine toxin
What does Yersinia murine toxin allow?
Survival in the flea midgut, resistance to antibacterial agents in the flea midgut
What allows Yersinia pestis to form a biofilm in the flea?
hma gene
Biofilm prevents the flea from?
Taking meals up, leads to regurgitation, the fleas starve and bite more frequently
What encodes the T3SS in Yersinia pestis?
pYv plasmid
Which plasmid encodes the T3SS?
pYv plasmid
Which plasmid encodes Yersinia murine toxin?
pFra
Which plasmid allows dissemination from the bite site, to the lymph nodes etc…?
pPst
What does pPst encode?
Pla plasminogen activator
Plasminogen activator allows the bacteria to do what?
Infect macrophages and reach the lymph nodes
Which plasmids were acquired by Yersinia pestis?
pPst
pFra
pYv
pYv plasmid encodes?
T3SS
pFra plasmid encodes?
Yersinia murine toxin
pPst plasmid encodes?
Pla plasminogen activator
Why is Yersinia pestis so virulent?
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
What bacteria causes anthrax?
Bacillus anthracis
Spore germination occurs?
Within macrophages
Where do spores form?
In the environment
Why might incidence with anthrax increase?
Due to global warming and thawing
What causes death by anthrax?
The toxins produced
The virulence factors are encoded on?
Two plasmids
What are the two plasmids of anthrax?
pXO1
pXO2
pXO2 produces?
Capsule proteins
Forms a protective coat
Inhibits phagocytosis
PXO1 produces?
The exotoxins
What are the exotoxins?
Edema and lethal toxin
What does edema toxin do?
Causes large swellings of pus and blood to form
What does lethal toxin do?
Leads to host death
How do the two exotoxins facilitate spread of anthrax?
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.
The two exotoxins are encoded by?
pXO1
What contributes to the high virulence of anthrax?
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.
