Lecture 6 pt 2

Question 1

Viruses and bacteria need hosts, how do they get them

Answer 1

Droplet transmission
Airborne transmission
Waterborne transmission
Vector transmission

Question 2

what is Droplet transmission —

Answer 2

for example, being passed along when one host accidentally sneezes on another. The flu is transmitted this way

Question 3

what is Airborne transmission —

Answer 3

for example, being exhaled by one host and inhaled by another. Tuberculosis is transmitted this way.

Question 4

what is Waterborne transmission —

Answer 4

leaving one host (e.g., in feces), infecting the water supply, and being taken up (e.g., in drinking water) by a new host. Cholera is transmitted this way

Question 5

what is Vector transmission —

Answer 5

getting picked up by a carrier (the vector — e.g., a mosquito) and carried to a new host. Malaria and Zika are transmitted this way

Question 6

what influences how “virulent” a virus or bacteria is

Answer 6

The form of transmission will influence how “virulent” a virus or bacteria is

Question 7

what is Virulence

Answer 7

is how much the virus/bacteria affects the host

We can think of virulence as the reproductive output of the virus:
highly virulent strains have created more offspring than less virulent ones BUT strains that are too virulent risk losing their host before being transmitted

Question 8

what is transmissibility

Answer 8

how easily they move from host to host

Question 9

what does natural selection favour

Answer 9

We predict that Natural Selection will favor viruses and bacteria that achieve a balance between their virulence (their reproductive output, how sick they make you) and their transmissibility (how easily they move from host to host)

Question 10

are sexually transmitted viruses more or less virulent

Answer 10

Thus, sexually transmitted viruses, for example, are generally less virulent because their hosts need to be reasonably active to transmit the virus

Question 11

what are examples of Flu viruses

Answer 11

H1N1 and the 1918 spanish flu

Question 12

what are examples of Filamentous viruses

Answer 12

hemorraghic fever viruses like marburg and ebola

Question 13

what are two major kinds of viruses

Answer 13

Filamentous viruses

Flu viruses

Question 14

what is an epidemic

Answer 14

is when new cases of a disease exceed expectation based on recent experience

Question 15

what is a pandemic

Answer 15

is a epidemic that has spread through a large region, for example multiple continents or even worldwide

Question 16

what else can we do with virus’s

Answer 16

We use them as tools: for gene therapy, for implanting false memories into mice, etc

Question 17

how hav viral infections have influenced human evolution

Answer 17

Our interactions with them over millions of years has resulted in additions and translocations to human DNA

Question 18

are viruses adaptable

Answer 18

XTREMELY

Question 19

What makes viruses so adaptable

Answer 19

Relatively simple construction
short generation time
(one virus can quickly replicate, become many viruses)
High mutation rates

Question 20

how are virus’s simple to construct

Answer 20

1) Made up of two or three parts:
Nucleic acid (can be RNA or DNA, we’ll discuss both)
Protein coat or capsid (contains the DNA/RNA)
Some have a lipid membrane or “envelope” covering the capsid
2) Viruses don’t replicate (copy themselves) on their own, they use the machinery from the host cell
3) DNA/RNA isn’t long and tied up with histones (like ours), but comes in small packets that are easily picked up and transcribed or incorporated into the host genome

Question 21

what is High mutation rates especially high in

Answer 21

RNA virus’s

Question 22

why is High mutation rates especially high in RNA virus’s

Answer 22

Because viral RNA polymerases lack proof-reading ability so there are just more frequent errors during copying
This can make it difficult to develop vaccines (because the genetic sequence is always changing)

Question 23

Influenza A viruses are divided into subtypes based on two surface proteins

Answer 23

the hemagglutinin (H) and the neuraminidase (N).

Question 24

what is Hemagglutinin

Answer 24

is important for binding and selectivity, it is the “key” to the cell’s “lock” from the video

Question 25

what is Neuraminidase is

Answer 25

important to let new copies of the virus out of the cell so they can infect other cells

Question 26

In their host species viruses often undergo ____ or ____ evolution, gradually changing through a process called antigenic drift

Answer 26

In their host species viruses often undergo slow or limited evolution, gradually changing through a process called antigenic drift

Question 27

what is Antigenic drift

Answer 27

: small changes in the virus that occur gradually through the accumulation of mutations
Over time, antibodies to a virus may not recognize new strains of the virus that result from this drift

Question 28

how is Antigenic drift different from genetic drift

Answer 28

unlike genetic drift, these are small, positive adaptations of the virus not small, random changes in allele frequency

Question 29

when viruses infect a new host they show ___ evolution

Answer 29

when viruses infect a new host they show rapid evolution

Question 30

what is Antigenic Shift:

Answer 30

Large, abrupt changes that occur, often because a cell has been infected by multiple viruses, for example viruses from more than one species

Such a “shift” occurred in the spring of 2009, when a new H1N1 virus with a new combination of genes emerged to infect people and quickly spread, causing a pandemic

Question 31

what happens to the people when such a shift occurs

Answer 31

When a shift happens, most people have little or no protection against the new virus

Question 32

what is H1N1 also caled

Answer 32

swine flu

Question 33

The H1N1 virus associated with the 2009 pandemic is an example of an _____

Answer 33

The H1N1 virus associated with the 2009 pandemic is an example of an antigenic shift involving viruses to three species (pig, bird, human)

Question 34

the H1N1 was a virus with parts of a viruses from multiple species such as:

Answer 34

the H1N1 was a virus with parts of a viruses from multiple species

1) A pig contracted a bird virus and a human virus
2) Bird and human viruses combined with swine virus that was in the pig
3) New bird-human-pig virus was transmitted from pig to human
4) New virus was then transmitted from human to human

Question 35

The H1N1 virus associated with the 2009 pandemic turned out to be ________

Answer 35

Highly transmissible but Not highly virulent

That is, it was easily passed from host to host (transmissible)
But most people just felt a little sick and then recovered, few people died (not very virulent).
That time, we were lucky But that’s not always the case…

Question 36

H1N1 2009 Pandemic
There was a lot of worry about this virus,
WHY?

Answer 36

H1N1 2009 Pandemic
There was a lot of worry about this virus,
WHY?
Because viruses from antigenic shifts result from such large, rapid changes, immune systems will be unable to recognize them
Humans have some immunity to other human viruses, but do not have immunity to viruses from other species
Shifted viruses can be highly virulent
It is also unpredictable how transmissible they will be

Question 37

1918 Spanish Flu devestation

Answer 37

Infected 500 million people and killed 50-100 million people (~2.5% of the population)

Question 38

This virus was strange for a few reasons (1918 spanish flu)

Answer 38

1) There were three waves of infection, very close together in time.
The SECOND wave was the most deadly
especially strange since you expect greater immunity during the second wave
2) Healthy, young adults had surprisingly high death rates
By comparison, seasonal flu kills <0.1% of the population annually
almost entirely very young or very old individuals (e.g. black line below) with weak or compromised immune systems
3.) Effects of the virus were really rapid
Virus activates the hosts inflammatory response
Triggers a tremendous immune response that destroys the hosts own cells
This could be why it’s so deadly in young adults, people 20-40 years old, because they have strong, active immune systems!

Question 39

was the 1918 spanish fee highly transmissible or virulent

Answer 39

the disease was both highly transmissible AND highly virulent