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?

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
Model for virulence evolution:
``` Virulence = T(v) x L(v) T(v) = rate of infections / reproduction rate L(v) = number of days virus is alive ```
26
What is the trade-off to maximize virulence?
More transmission & length host is alive to transmit
27
Ewald's Theory
Optimize replication rate / virulence by balancing high reproductive rates & host mortality
28
2 modes of disease transmission:
1. Direct host to host | 2. Vector
29
For host to host transmissions, what behaviour is needed to maximize virulence?
Low replication rate => low virulence | host must be alive to transmit
30
For vector transmission, what behaviour is needed to maximize virulence?
High replication rate => high virulent | host do not need to be alive
31
Which type of disease transmission causes higher mortality?
Vectorborne
32
Cholera is caused by...
Bacterium Vibrio cholerae
33
Symptoms of cholera
Diarrhea, dehydration
34
What is the vector for cholera?
Water, transmit the virus in poop
35
For diarrheal diseases, what is the relationship between fraction of waterborne outbreaks and deaths per infection?
More waterborne outbreaks = more deaths | can infect more people
36
How to lower virulence?
- Remove vectors - Increase hygiene - Isolate patients - Decrease host densities
37
When will pathogens evolve to be highly virulent?
When transmission between hosts is easy
38
Difference between PA Hypothesis and Ewald's theory?
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