BIO220 Lecture 8

Question 1

Virulence

Answer 1

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

Additional mortality rate that a pathogen imposed on the host.

Question 2

Impacts of the 1918 WWI influenza epidemic

Answer 2

Killed many people (highly virulent), then vanished

Question 3

What causes Ebola haemorrhagic fever?

Answer 3

Ebola virus

Question 4

Ebola virus causes…

Answer 4

Ebola haemorrhagic fever

Question 5

Ebola haemorrhagic fever

Answer 5

sever, fatal disease

Question 6

How is Ebola virus spread?

Answer 6

Air, contact

Question 7

Symptoms of Ebola haemorrhagic fever

Answer 7

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

Question 8

Where did the first Ebola outbreak happen?

Answer 8

Zaire & Sudan

Question 9

Where was the second time Ebola had an outbreak?

Answer 9

In monkeys that were imported into Virginia, USA

Question 10

Where was the last time Ebola had an outbreak?

Answer 10

Africa (5 diff locations)

Question 11

What is the “conventional wisdom” argument?

Answer 11

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

Question 12

Is the conventional wisdom correct in regards to virulence?

Answer 12

No

Question 13

How do humans come in contact with the Ebola virus?

Answer 13

Bats -> ape, chimp -> humans

Question 14

Do humans spread Ebola virus?

Answer 14

No, kills host too quickly

Question 15

SARS

Answer 15

Severe Acute Respiratory Syndrome

Question 16

SARS virus was so virulent because…

Answer 16

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

Question 17

What type of virus was responsible for SARS?

Answer 17

coronavirus: single stranded RNA virus.

Mixture of bird and other mammal viruses.

Question 18

Coronaviruses typically cause

Answer 18

Mild-moderate upper respiratory illnesses in humans

Question 19

What was the mortality rate for SARS?

Answer 19

5-10%

Question 20

What virus was used to kill rabbits?

Answer 20

Myxoma virus

Question 21

Why was the myxoma virus introduced?

Answer 21

Rabbit population exploded in Australia (brought from Europe)

Question 22

What happened to the virulence of myxoma virus?

Answer 22

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

Question 23

Level of virulence is caused by…

Answer 23

parasite replication rate in host

Question 24

Parasite adaptation hypothesis

Answer 24

Level of virulence = parasite replication rate.

Want to maximize replication rate to spread more.

Question 25

Model for virulence evolution:

Answer 25

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

Question 26

What is the trade-off to maximize virulence?

Answer 26

More transmission & length host is alive to transmit

Question 27

Ewald's Theory

Answer 27

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

Question 28

2 modes of disease transmission:

Answer 28

1. Direct host to host | 2. Vector

Question 29

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

Answer 29

Low replication rate => low virulence | host must be alive to transmit

Question 30

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

Answer 30

High replication rate => high virulent | host do not need to be alive

Question 31

Which type of disease transmission causes higher mortality?

Answer 31

Vectorborne

Question 32

Cholera is caused by...

Answer 32

Bacterium Vibrio cholerae

Question 33

Symptoms of cholera

Answer 33

Diarrhea, dehydration

Question 34

What is the vector for cholera?

Answer 34

Water, transmit the virus in poop

Question 35

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

Answer 35

More waterborne outbreaks = more deaths | can infect more people

Question 36

How to lower virulence?

Answer 36

- Remove vectors - Increase hygiene - Isolate patients - Decrease host densities

Question 37

When will pathogens evolve to be highly virulent?

Answer 37

When transmission between hosts is easy

Question 38

Difference between PA Hypothesis and Ewald's theory?

Answer 38

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