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BIO220 > BIO220 Lecture 8 > Flashcards

BIO220 Lecture 8 Flashcards

Virulence

1
Q

Virulence

A

Extent of harm an infection causes on you
(highly virulent = death)

Additional mortality rate that a pathogen imposed on the host.

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2
Q

Impacts of the 1918 WWI influenza epidemic

A

Killed many people (highly virulent), then vanished

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3
Q

What causes Ebola haemorrhagic fever?

A

Ebola virus

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4
Q

Ebola virus causes…

A

Ebola haemorrhagic fever

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5
Q

Ebola haemorrhagic fever

A

sever, fatal disease

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6
Q

How is Ebola virus spread?

A

Air, contact

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7
Q

Symptoms of Ebola haemorrhagic fever

A
  • High fever
  • Headache
  • Stomach & chest pain
  • Vomiting
  • Severe internal bleeding
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8
Q

Where did the first Ebola outbreak happen?

A

Zaire & Sudan

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9
Q

Where was the second time Ebola had an outbreak?

A

In monkeys that were imported into Virginia, USA

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10
Q

Where was the last time Ebola had an outbreak?

A

Africa (5 diff locations)

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11
Q

What is the “conventional wisdom” argument?

A

Pathogens and host will reach mutualistic association over time

  • Pathogen that have high virulence will kill host (and self)
  • High virulence pathogens are once that have recently invaded humans
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12
Q

Is the conventional wisdom correct in regards to virulence?

A

No

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13
Q

How do humans come in contact with the Ebola virus?

A

Bats -> ape, chimp -> humans

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14
Q

Do humans spread Ebola virus?

A

No, kills host too quickly

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15
Q

SARS

A

Severe Acute Respiratory Syndrome

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16
Q

SARS virus was so virulent because…

A

Most likely virus from another species that infected humans. Humans have no immunity at all.

17
Q

What type of virus was responsible for SARS?

A

coronavirus: single stranded RNA virus.

Mixture of bird and other mammal viruses.

18
Q

Coronaviruses typically cause

A

Mild-moderate upper respiratory illnesses in humans

19
Q

What was the mortality rate for SARS?

A

5-10%

20
Q

What virus was used to kill rabbits?

A

Myxoma virus

21
Q

Why was the myxoma virus introduced?

A

Rabbit population exploded in Australia (brought from Europe)

22
Q

What happened to the virulence of myxoma virus?

A

Went down (co-evolution between host and pathogen), but NOT TO ZERO. The virus still killed rabbits.

23
Q

Level of virulence is caused by…

A

parasite replication rate in host

24
Q

Parasite adaptation hypothesis

A

Level of virulence = parasite replication rate.

Want to maximize replication rate to spread more.

25
Q

Model for virulence evolution:

A 
Virulence = T(v) x L(v)
T(v) = rate of infections / reproduction rate
L(v) = number of days virus is alive
26
Q

What is the trade-off to maximize virulence?

A

More transmission & length host is alive to transmit

27
Q

Ewald’s Theory

A

Optimize replication rate / virulence by balancing high reproductive rates & host mortality

28
Q

2 modes of disease transmission:

A
  1. Direct host to host

2. Vector

29
Q

For host to host transmissions, what behaviour is needed to maximize virulence?

A

Low replication rate => low virulence

host must be alive to transmit

30
Q

For vector transmission, what behaviour is needed to maximize virulence?

A

High replication rate => high virulent

host do not need to be alive

31
Q

Which type of disease transmission causes higher mortality?

A

Vectorborne

32
Q

Cholera is caused by…

A

Bacterium Vibrio cholerae

33
Q

Symptoms of cholera

A

Diarrhea, dehydration

34
Q

What is the vector for cholera?

A

Water, transmit the virus in poop

35
Q

For diarrheal diseases, what is the relationship between fraction of waterborne outbreaks and deaths per infection?

A

More waterborne outbreaks = more deaths

can infect more people

36
Q

How to lower virulence?

A
  • Remove vectors
  • Increase hygiene
  • Isolate patients
  • Decrease host densities
37
Q

When will pathogens evolve to be highly virulent?

A

When transmission between hosts is easy

38
Q

Difference between PA Hypothesis and Ewald’s theory?

A

PA hypothesis:
Parasite will become less virulent the longer they are in the host because killing the host harms the parasite.
Ewald’s theory:
Optimize virulence by trading off between high reproductive rate and host mortality

BIO220 (24 decks)

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