Flashcards in BIO220 Lecture 9 Deck (63)
3 stages of virulence evolution
1. Accidental infection
2. Virulence evolution soon after invasion
3. Evolution of optimal virulence
Pathogens cross species boundaries
Mostly low virulent.
This rarely happens.
How might pathogens infect novel hosts?
- Infect one, but secondary infections won't happen
- Short-lived, high virulence infection that dies quickly
Why might accidental infections be very virulent?
Cross species, so new host as no immune defence against novel pathogen
Infection from host to host
What does successful invasion require?
Chain of host to host transmissions
Rapid increase in number of infected hosts
What happens during stage two of virulence evolution
Rapid evolution of pathogen and virulence
Many hosts infected
What happens during stage 3 of virulence evolution
Reach trade-off boundary between high & low virulence.
Evolution of pathogen slows, adaptation occurs.
Transmission frequency is optimized.
Problem with confirming death due to flu
Death is usually doe to associated illnesses, so difficult to confirm if flu was actually the cause.
Once you get one strain of the flu...
You are immune to that strain for life
Surface protein that allow virus to bind to target cell
Surface protein that allow virus to escape from host cell and infect other cells
Seasonal flu caused by
Pandemics are caused by...
Influenza A evolves...
Rapid evolution of the flu occurs at what sites on the virus?
HA and NA sites (recognized by the immune system)
Descendent of recent flu strains?
From single ancestor
What happens at antigenic sites on HA?
Continuous nucleotide substitutions
Where does mutations occur on HA and NA?
___ plays a strong role in determining influenza evolution
Human immune system
What do we use to make vaccines?
The most successful strain of the current year (most number of mutations)
How are vaccines tested?
When new strains of the virus appear, they are tested against current vaccines. If it does not work new vaccines must be made.
How long does it take to make a vaccine?
How are vaccines made?
Inactivated viruses cultured in eggs
How are viruses used for vaccines inactivated?
Damage nucleic acid by chemicals or radiation
What type of vaccine is used?
- 2 influenza A strains - H1N1, H3N2
- 1 influenza B strain
Main point of getting a vaccine
Stop transmission to OTHER people
3 types of the flu
1. Seasonal flu
2. Pandemic flu
3. Avian flu