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Flashcards in BIO220 Lecture 9 Deck (63):
1

3 stages of virulence evolution

1. Accidental infection
2. Virulence evolution soon after invasion
3. Evolution of optimal virulence

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Accidental infection

Pathogens cross species boundaries
Mostly low virulent.
This rarely happens.

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How might pathogens infect novel hosts?

- Infect one, but secondary infections won't happen
- Short-lived, high virulence infection that dies quickly

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Why might accidental infections be very virulent?

Cross species, so new host as no immune defence against novel pathogen

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Secondary infections

Infection from host to host

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What does successful invasion require?

Chain of host to host transmissions

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Epidemic

Rapid increase in number of infected hosts

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What happens during stage two of virulence evolution

Epidemic happens
Rapid evolution of pathogen and virulence
Many hosts infected

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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.

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Problem with confirming death due to flu

Death is usually doe to associated illnesses, so difficult to confirm if flu was actually the cause.

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Once you get one strain of the flu...

You are immune to that strain for life

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HA

Hemagglutinin protein
Surface protein that allow virus to bind to target cell

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NA

Surface protein that allow virus to escape from host cell and infect other cells

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Seasonal flu caused by

Influenza A

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Pandemics are caused by...

Influenza A

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Influenza A evolves...

very fast

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Rapid evolution of the flu occurs at what sites on the virus?

HA and NA sites (recognized by the immune system)

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Descendent of recent flu strains?

From single ancestor

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What happens at antigenic sites on HA?

Continuous nucleotide substitutions

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Where does mutations occur on HA and NA?

Antigenic sites

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___ plays a strong role in determining influenza evolution

Human immune system

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What do we use to make vaccines?

The most successful strain of the current year (most number of mutations)

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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.

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How long does it take to make a vaccine?

6 months

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How are vaccines made?

Inactivated viruses cultured in eggs

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How are viruses used for vaccines inactivated?

Damage nucleic acid by chemicals or radiation

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What type of vaccine is used?

Trivalent vaccine:
- 2 influenza A strains - H1N1, H3N2
- 1 influenza B strain

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Main point of getting a vaccine

Stop transmission to OTHER people

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3 types of the flu

1. Seasonal flu
2. Pandemic flu
3. Avian flu

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Seasonal flu

respiratory illness transmitted host-to-host. Immunity and vaccine available

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Pandemic flu

Global outbreak of a flu transmitted from host to host. No immunity.

32

Pandemic flus

1. 1918 Spanish flu
2. 1957 Asian flu
3. 1968 Hong Kong flu

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Avian flu

H5N1 virus found in birds:
deadly to domestic fowl and humans. No secondary infections.
No immunity, no vaccines.

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Antigenic drift

Accumulation of many small mutations

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Antigenic shift

Reassortment of RNA segments from different strains = gene flow

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The Spanish Flu was due to...

antigenic drift; an avian strain that was able to secondary infect

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Most influenza A viruses are descendent of...

1918 H1N1

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The H1N1 occurred in ___ waves, and ___ happened between waves.

3
Drift

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Who was most affected by the 1918 H1N1?

Young, old, middle age
(W shaped graph)

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Who is usually most affected by the flu?

Young and old people (U shaped graph)

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1918 H1N1 also appeared in what species?

Pigs

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What made up the 2009 H1N1 virus?

3 pig viruses, avian, human viruses
-> antigenic shift

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the 2009 H1N1 hit in ___ waves

2

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2009 H1N1 originated in...

Mexico

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Avian flu first appeared in...

Hong Kong

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Poliomyetlitis

Virus that causes poliomyelitis

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How do we get polio?

through the mouth

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Where does poliomyelitis replicate?

GI tract

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How is polio transmitted?

In feces

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Where does poliomyelitis affect?

GI tract, bloodstream, CNS

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what happens if the CNS is affected by polio?

Partial paralysis, maybe death

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IPV

Inactivated Polio Vaccine

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What is IPV inactivated with?

Formaldehyde

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How is IPV administered?

syringe

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OPV

Oral Polio Vaccine

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How was OPV made?

Selected for low virulence strains of polio in monkey kidneys. These live, non-virulent strains was used for vaccination.

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What are 2 advantages of OPV?

1. No needles needed
2. Vaccinated individual can vaccinate others

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VAPP

Vaccine Associated Paralytic Polio

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What caused VAPP?

Back mutations of OPV

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What is VAPP?

After successful vaccinations, there were still some polio outbreaks (not completely gone). These outbreaks were due to VAPP.

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Sequential vaccination

IPV first, then OPV
Combination increases effectiveness, and IPV will prevent back mutations of OPV

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Where did the polio outbreak in 2000 happen?

Haiti

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Why did the polio outbreak in 2000 happen?

OPV back mutation