BIO220 Lecture 9 Flashcards
Virulence II - Evolution of virulence - Evolution of influenza - Polio
3 stages of virulence evolution
- Accidental infection
- Virulence evolution soon after invasion
- Evolution of optimal virulence
Accidental infection
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
Secondary infections
Infection from host to host
What does successful invasion require?
Chain of host to host transmissions
Epidemic
Rapid increase in number of infected hosts
What happens during stage two of virulence evolution
Epidemic happens
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
HA
Hemagglutinin protein
Surface protein that allow virus to bind to target cell
NA
Surface protein that allow virus to escape from host cell and infect other cells
Seasonal flu caused by
Influenza A
Pandemics are caused by…
Influenza A
Influenza A evolves…
very fast
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?
Antigenic sites
___ 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?
6 months
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?
Trivalent vaccine:
- 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
- Seasonal flu
- Pandemic flu
- Avian flu
Seasonal flu
respiratory illness transmitted host-to-host. Immunity and vaccine available
Pandemic flu
Global outbreak of a flu transmitted from host to host. No immunity.
Pandemic flus
- 1918 Spanish flu
- 1957 Asian flu
- 1968 Hong Kong flu
Avian flu
H5N1 virus found in birds:
deadly to domestic fowl and humans. No secondary infections.
No immunity, no vaccines.
Antigenic drift
Accumulation of many small mutations
Antigenic shift
Reassortment of RNA segments from different strains = gene flow
The Spanish Flu was due to…
antigenic drift; an avian strain that was able to secondary infect
Most influenza A viruses are descendent of…
1918 H1N1
The H1N1 occurred in ___ waves, and ___ happened between waves.
3
Drift
Who was most affected by the 1918 H1N1?
Young, old, middle age
W shaped graph
Who is usually most affected by the flu?
Young and old people (U shaped graph)
1918 H1N1 also appeared in what species?
Pigs
What made up the 2009 H1N1 virus?
3 pig viruses, avian, human viruses
-> antigenic shift
the 2009 H1N1 hit in ___ waves
2
2009 H1N1 originated in…
Mexico
Avian flu first appeared in…
Hong Kong
Poliomyetlitis
Virus that causes poliomyelitis
How do we get polio?
through the mouth
Where does poliomyelitis replicate?
GI tract
How is polio transmitted?
In feces
Where does poliomyelitis affect?
GI tract, bloodstream, CNS
what happens if the CNS is affected by polio?
Partial paralysis, maybe death
IPV
Inactivated Polio Vaccine
What is IPV inactivated with?
Formaldehyde
How is IPV administered?
syringe
OPV
Oral Polio Vaccine
How was OPV made?
Selected for low virulence strains of polio in monkey kidneys. These live, non-virulent strains was used for vaccination.
What are 2 advantages of OPV?
- No needles needed
2. Vaccinated individual can vaccinate others
VAPP
Vaccine Associated Paralytic Polio
What caused VAPP?
Back mutations of OPV
What is VAPP?
After successful vaccinations, there were still some polio outbreaks (not completely gone). These outbreaks were due to VAPP.
Sequential vaccination
IPV first, then OPV
Combination increases effectiveness, and IPV will prevent back mutations of OPV
Where did the polio outbreak in 2000 happen?
Haiti
Why did the polio outbreak in 2000 happen?
OPV back mutation
