Evolution of virulence factors

Question 1

How does bacteria acquire virulence factors?

Answer 1

Often through horizontal gene transfer - pathogenic bacteria often has a non-pathogenic close relative

Question 2

What are the mechanisms of acquisition?

Answer 2

Transformation (uptake of DNA from environment), transduction (transferred by bacteriophages) and conjugation (whole plasmid transferred between bacteria)

Question 3

What are some theories on why pathogens harm their hosts?

Answer 3

“Avirulence” - virulence is just an accident when pathogen meets new host
“Coincidental evolution” - virulence an accidental byproduct that evolved in another context
“Trade-off” - natural selection finds optimal balance between rate of transmission and duration of infection

Question 4

What is the basic reproductive number?

Answer 4

How many one individual can spread the disease to - needs to be over 1 for the infection to spread through population.

Question 5

How is R0 calculated?

Answer 5

(Transmission x Number of possible hosts in pop.) / (Baseline mortality + pathogen induced mortality + host recovery)

Question 6

What is the effective reproductive number?

Answer 6

Expected number of new infections caused by an infectious individual in a population where some are immune. If below 1, the infection will die out.

Question 7

How is Re calculated?

Answer 7

R0 x (1-fraction of immune pop.)

Question 8

What are some factors that increase spread of zoonoses?

Answer 8

Increased population density, bad living conditions for farm animals, frequent contact with animals, smaller natural habitats, climate change