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Topic: Ebola evolved higher infectiousness during recent outbreak. (Read 288 times) previous topic - next topic

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  • VoxRat
  • wtactualf
Ebola evolved higher infectiousness during recent outbreak.
Two separate studies identified a single mutation in the ebolavirus  surface protein that resulted in more infectious (for humans) virus.
Human Adaptation of Ebola Virus during the West African Outbreak
Ebola Virus Glycoprotein with Increased Infectivity Dominated the 2013-2016 Epidemic

Washington Post summary here

The good news is that, with the human to human infection chain now broken, that mutant has a tougher time surviving in the reservoir (bats), so the next outbreak can't just pick up where the last one left off and build even greater infectivity on it.
"I understand Donald Trump better than many people because I really am a lot like him." - Dave Hawkins

  • meepmeep
  • Administrator
  • zombiecat queen
Re: Ebola evolved higher infectiousness during recent outbreak.
Reply #1
Did sfs make it over here or was he another casualty of the Great TR Zombification?

  • VoxRat
  • wtactualf
Re: Ebola evolved higher infectiousness during recent outbreak.
Reply #2
Haven't seen him here.  :(
"I understand Donald Trump better than many people because I really am a lot like him." - Dave Hawkins

Re: Ebola evolved higher infectiousness during recent outbreak.
Reply #3
Two separate studies identified a single mutation in the ebolavirus  surface protein that resulted in more infectious (for humans) virus.
Human Adaptation of Ebola Virus during the West African Outbreak
Ebola Virus Glycoprotein with Increased Infectivity Dominated the 2013-2016 Epidemic

Washington Post summary here

The good news is that, with the human to human infection chain now broken, that mutant has a tougher time surviving in the reservoir (bats), so the next outbreak can't just pick up where the last one left off and build even greater infectivity on it.
has the reservoir been demonstrated to be the reservoir? I thought there was still considerable ambiguity there.
Love is like a magic penny
 if you hold it tight you won't have any
if you give it away you'll have so many
they'll be rolling all over the floor

  • VoxRat
  • wtactualf
Re: Ebola evolved higher infectiousness during recent outbreak.
Reply #4
Two separate studies identified a single mutation in the ebolavirus  surface protein that resulted in more infectious (for humans) virus.
Human Adaptation of Ebola Virus during the West African Outbreak
Ebola Virus Glycoprotein with Increased Infectivity Dominated the 2013-2016 Epidemic

Washington Post summary here

The good news is that, with the human to human infection chain now broken, that mutant has a tougher time surviving in the reservoir (bats), so the next outbreak can't just pick up where the last one left off and build even greater infectivity on it.
has the reservoir been demonstrated to be the reservoir? I thought there was still considerable ambiguity there.
I don't think it's absolutely proved that bats are the reservoir.
But I've seen lots of evidence that they are, and no evidence that there's a better candidate.
"I understand Donald Trump better than many people because I really am a lot like him." - Dave Hawkins

  • sfs
Re: Ebola evolved higher infectiousness during recent outbreak.
Reply #5
Did sfs make it over here or was he another casualty of the Great TR Zombification?
Alas, I did not survive the great migration. I was swept overboard and lost at sea somewhere off the Azores. Tragic, really.

  • sfs
Re: Ebola evolved higher infectiousness during recent outbreak.
Reply #6
Two separate studies identified a single mutation in the ebolavirus  surface protein that resulted in more infectious (for humans) virus.
Human Adaptation of Ebola Virus during the West African Outbreak
Ebola Virus Glycoprotein with Increased Infectivity Dominated the 2013-2016 Epidemic

Washington Post summary here

The good news is that, with the human to human infection chain now broken, that mutant has a tougher time surviving in the reservoir (bats), so the next outbreak can't just pick up where the last one left off and build even greater infectivity on it.
It could still be lurking in a recovered patient, though. Ebola can apparently persist for a very long time.

  • VoxRat
  • wtactualf
Re: Ebola evolved higher infectiousness during recent outbreak.
Reply #7
Two separate studies identified a single mutation in the ebolavirus  surface protein that resulted in more infectious (for humans) virus.
Human Adaptation of Ebola Virus during the West African Outbreak
Ebola Virus Glycoprotein with Increased Infectivity Dominated the 2013-2016 Epidemic

Washington Post summary here

The good news is that, with the human to human infection chain now broken, that mutant has a tougher time surviving in the reservoir (bats), so the next outbreak can't just pick up where the last one left off and build even greater infectivity on it.
It could still be lurking in a recovered patient, though. Ebola can apparently persist for a very long time.
There is that.  :ohdear:

You would probably know better than anyone else I know...
Is there molecular-epidemiological evidence that any outbreaks to date have come from such a source, as opposed to separate "spillover" events?
"I understand Donald Trump better than many people because I really am a lot like him." - Dave Hawkins

  • sfs
Re: Ebola evolved higher infectiousness during recent outbreak.
Reply #8
Two separate studies identified a single mutation in the ebolavirus  surface protein that resulted in more infectious (for humans) virus.
Human Adaptation of Ebola Virus during the West African Outbreak
Ebola Virus Glycoprotein with Increased Infectivity Dominated the 2013-2016 Epidemic

Washington Post summary here

The good news is that, with the human to human infection chain now broken, that mutant has a tougher time surviving in the reservoir (bats), so the next outbreak can't just pick up where the last one left off and build even greater infectivity on it.
It could still be lurking in a recovered patient, though. Ebola can apparently persist for a very long time.
There is that.  :ohdear:

You would probably know better than anyone else I know...
Is there molecular-epidemiological evidence that any outbreaks to date have come from such a source, as opposed to separate "spillover" events?
Aside from a couple of late infections derived from the West Africa outbreak, this is the only possible indication of a such an occurrence that I'm aware of: http://jvi.asm.org/content/89/19/10130.full. (Somebody only pointed this paper out to me today.)

There was considerable disagreement in our group about whether the EBOV glycoprotein mutations affected the course of the outbreak.

  • meepmeep
  • Administrator
  • zombiecat queen
Re: Ebola evolved higher infectiousness during recent outbreak.
Reply #9
What's the argument for saying the mutations didn't affect the course of the outbreak? Is it that the mutations didn't conclusively have the effect being claimed or is it that outside factors, like infrastructure, slow response, etc., were more to blame?

I'm curious about the bit that the mutations made the virus less likely to infect bats. Reverse zoonosis is shockingly under-studied in general, except for influenza monitoring, and it's interesting to me that they thought to test this out.

  • sfs
Re: Ebola evolved higher infectiousness during recent outbreak.
Reply #10
What's the argument for saying the mutations didn't affect the course of the outbreak? Is it that the mutations didn't conclusively have the effect being claimed or is it that outside factors, like infrastructure, slow response, etc., were more to blame?
The evidence is that this mutation (along with several others) increases infectivity of human cells. It's a reasonable bet that it alters the course of the infection of an individual. But that may not translate into greater transmissibility. If a mutation causes a more infectious virus to kill you more quickly, it may reduce transmission rather than increase it. The epidemiological evidence is that the mutated virus reentered Guinea several times, each time causing flare-ups that ultimately died out, while the wild type continued chugging along in Guinea throughout the epidemic. This view was championed by Andrew Rambaut, who is The Man when it comes to molecular viral evolution.

On the other hand, we only investigated three mutations, selected because they were potentially functional and achieved high frequency in the outbreak. Of those three, one shows good evidence for human adaptation, one doesn't, and one needs more work. If we assume most functional mutations are not beneficial, then the prior probability of hitting on one by chance is small, and so the posterior probability that the functional effect caused the high frequency is high. Furthermore, a mutation that causes such an important phenotypic change is likely to have some effect on overall fitness, and the high frequency of the mutation argues against it being detrimental. That's my view, and that of Pardis Sabeti.

Quote
I'm curious about the bit that the mutations made the virus less likely to infect bats. Reverse zoonosis is shockingly under-studied in general, except for influenza monitoring, and it's interesting to me that they thought to test this out.
I think the main reason for testing the bat cells is to show that this is adaptive specifically in primates, and maladaptive in the reservoir.

  • meepmeep
  • Administrator
  • zombiecat queen
Re: Ebola evolved higher infectiousness during recent outbreak.
Reply #11
The evidence is that this mutation (along with several others) increases infectivity of human cells. It's a reasonable bet that it alters the course of the infection of an individual. But that may not translate into greater transmissibility. If a mutation causes a more infectious virus to kill you more quickly, it may reduce transmission rather than increase it. The epidemiological evidence is that the mutated virus reentered Guinea several times, each time causing flare-ups that ultimately died out, while the wild type continued chugging along in Guinea throughout the epidemic. This view was championed by Andrew Rambaut, who is The Man when it comes to molecular viral evolution.

That makes sense. Do we know how the mutated type reentered? Wouldn't it be fairly improbable that the mutation arose independently more than once? Or is that within the realm of possibility?

On the other hand, we only investigated three mutations, selected because they were potentially functional and achieved high frequency in the outbreak. Of those three, one shows good evidence for human adaptation, one doesn't, and one needs more work. If we assume most functional mutations are not beneficial, then the prior probability of hitting on one by chance is small, and so the posterior probability that the functional effect caused the high frequency is high. Furthermore, a mutation that causes such an important phenotypic change is likely to have some effect on overall fitness, and the high frequency of the mutation argues against it being detrimental. That's my view, and that of Pardis Sabeti.

Can both things be true? I mean, we know from looking at other pathogens that while a higher level of virulence can lead to an evolutionary dead end, it can also sometimes be advantageous, depending on the circumstances. As an example, I remember reading once that cholera has evolved to be more virulent in areas with inadequate water sanitation and less virulent in areas that are more developed and better equipped to handle waste disposal. At the same time, it's hard to imagine that the specific circumstances of the people infected with the wild type versus the more virulent type would be so different as to lead to different selective pressures, and the fact that the more virulent type ultimately died out after several different flare-ups still suggests the wild type is more fit overall. I assume the mutated type led to a shorter incubation period and more rapid onset of more severe symptoms, so could it be that this mutation was seen with such high frequency because this type happened to be getting a foothold by infecting people in cramped, close quarters who had many more opportunities for exposure? And that once those conditions were altered by people changing their behavior, like avoiding the area or taking extra precautions in handling infectious waste or the dead, that the mutation ceased to be all that beneficial?