37. Virus-Host Interactions Flashcards
4 examples of host-virus interactions
- viruses are obligate intracellular parasites
- viruses hijack/rely on cellular factors, pathway, resources
- cellular antiviral mechanisms
- co-evolution of viruses and hosts –> arms race
4 levels of host-virus interactions
- molecular level
- cellular level
- organism level
- population level
^all interact with each other
describe the cross-talk btwn systems at the organism level
cytokines act on neurons to help control transmission and neurotransmitters can act on immune cells
3 viruses that have transmitted across species
- influenza
- yellow fever
- HIV
why do not all viruses transmit between animals?
viruses adapt to an animal so when they transmit to another animal they must RE-ADAPT
3 animals that transmit influenza to humans
- pigs
- poultry
- cats
what happens in carrier animals for influenza?
influenza undergoes reassortment
describe the transmission of yellow fever virus
back and forth btwn mosquito and non-human primate then transmit to human
transmission of AIDS
from SIV in non-human primates
mangabey –> humans for HIV2
chimpanzee –> humans for HIV1
What are the only 2 retroviruses circulating in humans?
- HIV
- HTLV
why did they sequence SIV from macaque (SIVmac)?
to help understand HIV2 origin
what did they find was related to SIVmac and HIV2? and the significance?
found that SIVsm is related to SIVmac and HIV2
therefore, SIVsm has infected macaques in captivity and humans and evolved to SIVmac and HIV2
what is the origin of HIV1?
SIV chimpanzee
2 chimpanzee species with SIV, which one has transmitted SIV to humans?
- Troglodytes
- Schweinfurthii
only troglodytes have transmitted SIV to humans for HIV1
name and explain the 4 groups of HIV1
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
how did SIVs cross the species barrier and adapt to humans?
counteracts antiviral protein/restriction factor TETHERIN so it can infect
how do viruses have to adapt to tetherin to infect?
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
how do viral restriction factors determine host tropism?
the viral restriction factors in the cell can inhibit viral infection –> determines which species can be infected
3 types of selection and the ratio
- positive selection
- neutral selection
- purifying selection
describe the selection ratio
dN/dS
dN = non-synonymous mutation in nt that changes aa code
dS = synonymous mutation in nt that doesn’t change aa code
describe positive selection
dN/dS > 1
more non-synonymous mutations, more aa are changed
describe neutral selection
dN/dS = 1
no pressure for viral or host to change
describe purifying selection
dN/dS < 1
more synonymous mutations that don’t change aa –> aa cannot change or else protein loses its function
what type of restriction do viral restriction factors undergo?
positive selection
example of virus-host arms race with host restriction factor
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
3 ways that hosts keep up in the arms race
- polymorphisms in the population
- host heterozygosity
- gene duplication and innovation
