Chapter 6: Viruses

Question 1

How are viruses constructed?

Answer 1

-Very simple construction
-Bundles of RNA or DNA covered by layers of proteins and lipids

Question 2

What are the two types direct transmission ?

Answer 2

-person-to-person contact: coming in contact with a person or their bodily fluids. (HIV, ebola)
-droplet transmission: for ex then sneezing, respiratory droplets (large), droplet nuclei (small). (Influenza and COVID19)

Question 3

What are the three types of indirect transmission?

Answer 3

-Airborne
-Vector
-Waterborne

Question 4

How does airborne transmission work?

Answer 4

Droplet nuclei are suspended in the air and enter the respiratory system:
-requires that virus survive long periods outside of host
-diff from droplet transmission because droplet not needed
-Tuberculosis, chickenpox, smallpox, measles

Question 5

How does vector transmission work?

Answer 5

-Getting picked up by a carrier (eg. mosquito)
-Malaria

Question 6

How does waterborne transmission work?

Answer 6

-leaving host (eg. feces), infecting water supply and being taken up (eg drinking water) by a new host.
-cholera

Question 7

What is the relation between the form of transmission and the virulence of the virus ?

Answer 7

-Form of transmission will influence the virulence of virus or bacteria
-Virulence is the reproductive output of the virus
-Highly virulent create more offspring but less chance of transmission because host in not in capacity of being gout in contact with others
-Less virulent create less offspring but more chance of transmission because host is well enough to be out in contact with others.

Question 8

What are the three major kinds of viruses?

Answer 8

-Flu viruses (H1N1 and Spanish flu)
-Filamentous viruses (ebola)
-Coronaviruses (COVID 19, SARS, MERS)

Question 9

What are the different terms of scale for viruses?

Answer 9

-Outbreak: town
-Epidemic: province
-Pandemic: across the world

Question 10

How is the relationship between humans and viruses complicated?

Answer 10

-Over mills of years, our interactions with viruses has resulted in additions and translocations to human DNA
-influenced human evolution

Question 11

What makes viruses so adaptable?

Answer 11

1) Relatively simple construction
2)Short generation time
3)High mutation rates

Question 12

Why are viruses so simply constructed?

Answer 12

-Don’t replicate on their own
-They use the machinery from the host cells
-So they need fewer genes and protein
-Not alive: don’t need to eat digest etc…

Question 13

Why are viruses so short in generation time?

Answer 13

-Reproduces quickly
-DNA/RNA comes in small packets, easily picked up and quickly copied

Question 14

Why do viruses have high mutation rates?

Answer 14

-Especially true in RNA viruses
-Proteins that copy RNA lack proof-reading ability, so more frequent errors during copying, so more mutations
-Makes it difficult to develop vaccines

Question 15

What are the proteins on the surface of the virus important for?

Answer 15

-Important for attaching to and entering cells. -Called the “keys”
-How the immune system recognises a virus

Question 16

What do different viruses vary in?

Answer 16

-structure
-surface proteins
-effects on the host

Question 17

What will the capacity of a virus to evade immune response depend on?

Answer 17

How rapidly the surface proteins change

Question 18

What is antigenic drift?

Answer 18

• small changes in the virus that occur gradually through the accumulation of mutations
  -Overtime with enough mutation, antibodies to a virus may not recognize new strains of the virus that result from this drift

Question 19

How does the influenza virus evolve?

Answer 19

-During winter
-Starts in Southern Hemisphere and move north
-Genetic drift: seasonal flu will change over the course of the year
-This is why annual flu vaccines are updated 2x a year

Question 20

What is antigenic shift?

Answer 20

-Rapid evolution when they infect a new host species
-Large, abrupt changes that occur often because a cell has been infected by multiple viruses (from more than one species)
-No protection/immunity against the new virus

Question 21

What is an endemic?

Answer 21

-Disease constantly present
-Spread and rates are predictable

Question 22

Can a virus undergoing antigenic drift cause an epidemic or pandemic?

Answer 22

No cause changes are too small

Question 22

Can a virus undergoing antigenic drift cause an epidemic or pandemic?

Answer 22

No cause changes are too small

Question 23

What are influenza virus subtypes based on?

Answer 23

Two surface proteins:
-Hemagglutinin: binding and selectivity, “key” to the cell, 16 of them.
-Neuraminidase: let the new copies out of the cell, 9 of them

Question 24

How did H1N1 2009 pandemic erupt ?

Answer 24

-"swine flu" -antigenic shift involving viruses from pig, bird and human -these combined to create anew H1N1 with parts of viruses from multiple species

Question 25

Why was there alot of worry about H1N1?

Answer 25

-Antigenic shift results in immune systems not able to recognize the virus -No natural immunity to viruses fro other species -So potential for high virulence -Unpredictable how transmissible it will be

Question 26

How did H1N1 end up being?

Answer 26

-highly transmissible -not highly virulent

Question 27

How many people were killed in the 1918 Spanish flu pandemic ?

Answer 27

Killed roughly 2,5% of the world's population

Question 28

Why was the 1918 flu strange?

Answer 28

1) Three waves of infection, very close together in time 2) Healthy young adults had high death rates 3)Effects the virus were really rapid

Question 29

Why were the three waves of infection strange during the 1918 flu?

Answer 29

-Second wave=most deadly -Strange because should expect greater immunity during second wave

Question 30

Why was it surprising that healthy young adults had high death rates?

Answer 30

Compared to seasonal flu that killed almost entirely very young or very old individuals with weak or compromised immune systems

Question 31

Why were the effects of the virus really rapid?

Answer 31

-Virus activated hosts inflammatory response -Triggered big immune response that destroyed hosts own cells -This was probs why young adults were very sensitive is they had strong immune systems

Question 32

Did the 1918 flu disappear?

Answer 32

-No it is the ancestor of all seasonal and pandemic flu over the last century -How? immunity to 1918 flu then small mutations through antigenic drift

Question 33

What do we think seasonal flu stemmed from?

Answer 33

-Bird virus that had moved to humans in 1918 -But in 1918, that virus went to pigs! We still see swine flu in pigs every year

Question 34

How did the 1918 flu become H1N1?

Answer 34

-The swine flu from pigs shaped genes with a different bird flu and different human flu and became H1N1

Question 35

Who is the nature host for filoviruses (ebola)?

Answer 35

-Fruit Bats -Serve as a reservoir for the virus -Have immunity, so the virus co-exists with them -Virus isn't rapidly changing in bats

Question 36

What is enzootic and epizootic cycle?

Answer 36

-Enzootic cycle: transmission of virus within bats -Epizootic cycle: transmission of virus between bats and other wild animals

Question 37

How lethal is ebola in African strains?

Answer 37

-70-90% of cases of infection

Question 38

How are the symptoms of ebola?

Answer 38

-Early symptoms: like a bad flu -Late symptoms: gastrointestinal bleeding, swelling of the eyes and genitals, pain in the skin, hemorrhagic rashes.

Question 39

How does ebola produce its very strong effects?

Answer 39

-Infects macrophages (part of immune system) -These macro release cytokines -That increases the permeability of your blood vessels which allows blood to leak out from them -So immune system can't combat infection

Question 40

Why do we argue that Ebola has limited success in humans?

Answer 40

-Swift and lethal -But then why 1918 flu so successful? Diff in transmission, ebola has less chance of transmission because require close contact with body fluids

Question 41

How many people can a person with ebola infect on average?

Answer 41

2

Question 42

What are measures to take to prevent further spread of ebola?

Answer 42

-quarantine -protective equipment -disposal of waste -proper burial

Question 43

If ebola is not easily contagious, how did it happen in 2014?

Answer 43

-It happened in more densely populated areas

Question 44

If the spread of ebola is about population density, then why did Nigeria get away pretty well?

Answer 44

-Good luck -They were able to stop the spread: first case was Patrick Sawyer who was sick upon arriving at the airport, doctor Ameyo Adadevoh identified the disease and and immediately placed him in quarantine.

Question 45

What are coronaviruses named after?

Answer 45

Named for the spikes on their surface.

Question 46

How was the first major Coronavirus discovered?

Answer 46

-Before 2003: two coronaviruses known to infect humans, caused mild illness -In 2003: Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) was the first coronavirus to cause a pandemic.

Question 47

Via what animals have Coronaviruses spread to humans?

Answer 47

2003: Bats--Pal-masked civets---SARS CoV 2012: Bats--Camels---MERS-CoV 2019: Bats--Pangolins--SARS-CoV2

Question 48

How is SARS CoV2 transmitted?

Answer 48

-respiratory droplets (small and large) -some debate about whether it is airborne

Question 49

What matters about droplet transmission for CoV2?

Answer 49

1) Location matters (ex. where you're located in a room full of people) 2)Time matters (ex. how long you stay in a room full of people)

Question 50

How do you get COVID19 from SARS CoV2?

Answer 50

-Infects epithelial cells in the lungs -Symptoms are similar to mild cases of pneumonia

Question 51

What happens during a cytokine storms?