37. Virus-Host Interactions

Question 1

4 examples of host-virus interactions

Answer 1

1. viruses are obligate intracellular parasites
2. viruses hijack/rely on cellular factors, pathway, resources
3. cellular antiviral mechanisms
4. co-evolution of viruses and hosts –> arms race

Question 2

4 levels of host-virus interactions

Answer 2

1. molecular level
2. cellular level
3. organism level
4. population level

^all interact with each other

Question 3

describe the cross-talk btwn systems at the organism level

Answer 3

cytokines act on neurons to help control transmission and neurotransmitters can act on immune cells

Question 4

3 viruses that have transmitted across species

Answer 4

1. influenza
2. yellow fever
3. HIV

Question 5

why do not all viruses transmit between animals?

Answer 5

viruses adapt to an animal so when they transmit to another animal they must RE-ADAPT

Question 6

3 animals that transmit influenza to humans

Answer 6

1. pigs
2. poultry
3. cats

Question 7

what happens in carrier animals for influenza?

Answer 7

influenza undergoes reassortment

Question 8

describe the transmission of yellow fever virus

Answer 8

back and forth btwn mosquito and non-human primate then transmit to human

Question 9

transmission of AIDS

Answer 9

from SIV in non-human primates

mangabey –> humans for HIV2

chimpanzee –> humans for HIV1

Question 10

What are the only 2 retroviruses circulating in humans?

Answer 10

1. HIV
2. HTLV

Question 11

why did they sequence SIV from macaque (SIVmac)?

Answer 11

to help understand HIV2 origin

Question 12

what did they find was related to SIVmac and HIV2? and the significance?

Answer 12

found that SIVsm is related to SIVmac and HIV2

therefore, SIVsm has infected macaques in captivity and humans and evolved to SIVmac and HIV2

Question 13

what is the origin of HIV1?

Answer 13

SIV chimpanzee

Question 14

2 chimpanzee species with SIV, which one has transmitted SIV to humans?

Answer 14

1. Troglodytes
2. Schweinfurthii

only troglodytes have transmitted SIV to humans for HIV1

Question 15

name and explain the 4 groups of HIV1

Answer 15

Group M –> cause of HIV pandemic
Group N –> less than 20 infections in Cameroon
Group O –> 100,000 infections in west central Africa
Group P –> 2 cases

Question 16

how did SIVs cross the species barrier and adapt to humans?

Answer 16

counteracts antiviral protein/restriction factor TETHERIN so it can infect

Question 17

how do viruses have to adapt to tetherin to infect?

Answer 17

tetherin differs btwn diff species –> when SIV switches from apes to humans, the original viral antagonist cannot recognize tetherin so it must change the viral protein to infect

Question 18

how do viral restriction factors determine host tropism?

Answer 18

the viral restriction factors in the cell can inhibit viral infection –> determines which species can be infected

Question 19

3 types of selection and the ratio

Answer 19

1. positive selection
2. neutral selection
3. purifying selection

Question 20

describe the selection ratio

Answer 20

dN/dS

dN = non-synonymous mutation in nt that changes aa code

dS = synonymous mutation in nt that doesn’t change aa code

Question 21

describe positive selection

Answer 21

dN/dS > 1

more non-synonymous mutations, more aa are changed

Question 22

describe neutral selection

Answer 22

dN/dS = 1

no pressure for viral or host to change

Question 23

describe purifying selection

Answer 23

dN/dS < 1

more synonymous mutations that don’t change aa –> aa cannot change or else protein loses its function

Question 24

what type of restriction do viral restriction factors undergo?

Answer 24

positive selection

Question 25

example of virus-host arms race with host restriction factor

Answer 25

viral antagonist interacts with host restriction factor
- restriction factor degraded and allows viral replication

then host restriction factor is mutated to regain antiviral activity

then viral antagonist is mutated to regain viral activity

Question 26

3 ways that hosts keep up in the arms race

Answer 26

1. polymorphisms in the population
2. host heterozygosity
3. gene duplication and innovation