Obsessing about COVID-19
Feb. 1st, 2021 12:21 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
garoteI'm not an evolutionary biologist, so this is really just a thought exercise for me. But the discovery that COVID-19 is evolving as it spreads through humans has led me to a troubling question, and before I ask it I need to work my way over to it.
There is stuff all around us - all over us - fungal infections and parasites - that spreads through touch and thrives in all kinds of corners, and if the immune system wasn’t tuned to fight it viciously, it would digest our bodies into dead sludge in a matter of days.
The more effectively a disease kills people, the higher the selection pressure it makes for the next round of people to be resistant, so naturally our immune system evolved to fight the biggest threats hardest. Viruses that we get occasionally - like once a year - apply less pressure, especially if they just weaken us, rather than killing us, so we can keep spreading them. Viruses are always learning this lesson: There's no money in being fatal.
So, the fact that COVID-19 has plenty of room to mutate into more virulent forms means what in this context?
It means that it has not had much selection pressure for this kind of virulence applied to it in the past. That means two things: There wasn't pressure to be virulent in an environment like the modern human one, and, there was pressure to be virulent in some other environment instead.
What was that other environment; that one that it's evolving away from?
Well, so far COVID-19 has not done well surviving on surfaces. So we can imagine a past environment where surfaces were very favorable for it. Dark, room temperature, humid. Or, an environment where animals were often touching the same surface - or each other - multiple times a day, or not at all, so there wasn't much profit in surviving long.
COVID-19, as a coronavirus, can spread through breath and touching, and also through poop. COVID-19 infection is easily detected in poop, so it came from some environment where it was valuable to prioritize that. So: Situations where critters were exposed to each others' poop. A critter that pooped out in the woods away from their den, for example, would not be ideal. This points to a virus that targeted critters who stayed planted in one spot long enough to poop directly in or around it.
COVID-19 is also known to have rapid onset of intense symptoms in some hosts. Mild symptoms that came on slowly were apparently not ideal for it in the past: The animal had to be nearly incapacitated quickly. That would not work as well in animals that were divided into small families -- milder symptoms would be better for carrying it long enough to reach another family. But, it would work well in animals that gathered in big multi-family colonies: The animal gets so suddenly ill that it can't leave the colony, and just hunkers down where it is, spreading to everyone that jostles by. Then the disease reaches another animal who expresses no symptoms, and feels well enough to go out long-term, perhaps even reaching another colony.
This fits the profile of a bat or bird colony, and the genetic analysis of COVID-19 confirms that it's most closely related to strains previously confined to bats.
By the way, this also assumes that COVID-19 manifested in its previous carrier the same way it currently does in humans. I don't know enough about coronaviruses to know how likely that is.
So, what environment is COVID-19 now being pressured to evolve to fit?
In public, the surfaces that humans tend to touch collectively with their skin are mostly door handles, handrails, buttons, chair backs, countertops, and the hands of cashiers. Except for the hands, these are usually metallic or plastic or glass, or less often some kind of cloth or vinyl. COVID is now under pressure to survive longer on those surfaces.
Humans have access to indoor plumbing and sewage treatment. Spreading through the vector of poop is now way less useful. We should expect COVID to appear less there.
Humans tend to socialize when they are feeling well, and go home when their symptoms are bad. COVID is under pressure to show fewer symptoms, slower, while continuing to be virulent. Severe reactions are less useful.
People face each other and flap their mouths, from a distance of a few feet, in temperature controlled closed spaces, a great deal of time. This makes breath an incredibly valuable vector for any disease to spread. COVID is now under intense pressure, worldwide, to get better at hopping from lung to lung, and that pressure is getting results: The virus has refined itself in multiple different strains, all just a bit better at this in some way.
It will be very interesting to know the mechanisms, if we can ever sort them out. Does the more virulent strain of COVID work by making people feel less feverish, so they're inclined to go out, but also shorter of breath so they have to breathe harder? Or, does it make them more feverish so they want to stay indoors when it's cold, exposing them to more indoor situations? Does it replicate more in the lungs and less in the gut? Does it show symptoms later, so people carry it unknowingly for longer? Does it mess with them neurologically, and make them feel more gregarious, or more lonely? Or more aggressive?
That would be amazing: If COVID-19 actually spawned more riots by directly messing with people's hormones, rather than the (already very plausible) frustration created by social distancing. My money's not on it, but it would be amazing.
Add up these selection pressures, and what you get is a target very much like that of the seasonal flu. And what do you know; the motley gang of viruses that cause the so-called "common cold" includes several coronaviruses. In other words, this exact scenario has probably already happened multiple times: A virus causing a dangerous pandemic doesn't go away, it gets forcefully evolved into just another agent for the "common cold".
Now there's a vaccine out. So far, the vaccine is thought to be effective against all strains of COVID-19, because all strains of COVID-19 use the same "spike protein" to gain access to cells. This is a gigantic inoculation on top of the regular flu-season inoculation, in the fight against what is essentially a monstrous, untamed incarnation of the flu -- in consequences, even if not in morphology. What are the chances that, the same way the flu does, COVID-19 will manage to stumble onto a different spike protein, and we'll need to retool our vaccines for it and re-apply them next year?
Now I have to soberly consider the prospect that we will put a boot down on the worst of COVID-19 ... and then we will need to do the same thing again for its slightly less fatal sequel one or two years later ... and so on, for five, or ten, or twenty years.
Picture the current social distancing standard, in slowly decreasing severity, not for one more year but for twenty. When will you consider it proper to throw away the mask, and sit down inside a restaurant, the way we all still picture restaurants in our heads? Given the enormous trouble we've all had sorting out the tested science from the noise, there will be a certain amount of personal, subjective choice at work. What's your yardstick? A death rate matching the flu? Less severe symptoms? The entire world immunized once? A yearly immunization in place, with no clear end? Total yearly deaths only twice that of the flu? (After about a year we are currently up to 2.2 million dead worldwide. The seasonal flu kills about 1/4th that many people.)
Or perhaps you will decide that none of this is adequate, and resolve to wear the mask and avoid indoor gatherings for as long as it takes. If there are enough of us doing that, social customs and city planning and architecture will all slowly bend in a new direction for decades. Theaters, concert halls, bathrooms, meeting rooms, restaurants, entire schools ... millions of them ... all will need to be reconfigured or perhaps just destroyed.
What if doing things that way could prevent ten million deaths, but human civilization collectively decides that one year of vaccine distribution is our triumphant moment, because we all damn well need to get back to work and back into classrooms and restaurants, and the next strain of COVID-19 is declared to be "only as bad as the flu" and folded into the pipeline of flu shot distribution ... and then a year later, a million more people have died?
I really hope one good vaccination hammer blow is enough to knock COVID-19 into the background. Otherwise, somewhere, we are all going to need to bring the science and the economics to bear, and draw an unpleasant line.
There is stuff all around us - all over us - fungal infections and parasites - that spreads through touch and thrives in all kinds of corners, and if the immune system wasn’t tuned to fight it viciously, it would digest our bodies into dead sludge in a matter of days.
The more effectively a disease kills people, the higher the selection pressure it makes for the next round of people to be resistant, so naturally our immune system evolved to fight the biggest threats hardest. Viruses that we get occasionally - like once a year - apply less pressure, especially if they just weaken us, rather than killing us, so we can keep spreading them. Viruses are always learning this lesson: There's no money in being fatal.
So, the fact that COVID-19 has plenty of room to mutate into more virulent forms means what in this context?
It means that it has not had much selection pressure for this kind of virulence applied to it in the past. That means two things: There wasn't pressure to be virulent in an environment like the modern human one, and, there was pressure to be virulent in some other environment instead.
What was that other environment; that one that it's evolving away from?
Well, so far COVID-19 has not done well surviving on surfaces. So we can imagine a past environment where surfaces were very favorable for it. Dark, room temperature, humid. Or, an environment where animals were often touching the same surface - or each other - multiple times a day, or not at all, so there wasn't much profit in surviving long.
COVID-19, as a coronavirus, can spread through breath and touching, and also through poop. COVID-19 infection is easily detected in poop, so it came from some environment where it was valuable to prioritize that. So: Situations where critters were exposed to each others' poop. A critter that pooped out in the woods away from their den, for example, would not be ideal. This points to a virus that targeted critters who stayed planted in one spot long enough to poop directly in or around it.
COVID-19 is also known to have rapid onset of intense symptoms in some hosts. Mild symptoms that came on slowly were apparently not ideal for it in the past: The animal had to be nearly incapacitated quickly. That would not work as well in animals that were divided into small families -- milder symptoms would be better for carrying it long enough to reach another family. But, it would work well in animals that gathered in big multi-family colonies: The animal gets so suddenly ill that it can't leave the colony, and just hunkers down where it is, spreading to everyone that jostles by. Then the disease reaches another animal who expresses no symptoms, and feels well enough to go out long-term, perhaps even reaching another colony.
This fits the profile of a bat or bird colony, and the genetic analysis of COVID-19 confirms that it's most closely related to strains previously confined to bats.
By the way, this also assumes that COVID-19 manifested in its previous carrier the same way it currently does in humans. I don't know enough about coronaviruses to know how likely that is.
So, what environment is COVID-19 now being pressured to evolve to fit?
In public, the surfaces that humans tend to touch collectively with their skin are mostly door handles, handrails, buttons, chair backs, countertops, and the hands of cashiers. Except for the hands, these are usually metallic or plastic or glass, or less often some kind of cloth or vinyl. COVID is now under pressure to survive longer on those surfaces.
Humans have access to indoor plumbing and sewage treatment. Spreading through the vector of poop is now way less useful. We should expect COVID to appear less there.
Humans tend to socialize when they are feeling well, and go home when their symptoms are bad. COVID is under pressure to show fewer symptoms, slower, while continuing to be virulent. Severe reactions are less useful.
People face each other and flap their mouths, from a distance of a few feet, in temperature controlled closed spaces, a great deal of time. This makes breath an incredibly valuable vector for any disease to spread. COVID is now under intense pressure, worldwide, to get better at hopping from lung to lung, and that pressure is getting results: The virus has refined itself in multiple different strains, all just a bit better at this in some way.
It will be very interesting to know the mechanisms, if we can ever sort them out. Does the more virulent strain of COVID work by making people feel less feverish, so they're inclined to go out, but also shorter of breath so they have to breathe harder? Or, does it make them more feverish so they want to stay indoors when it's cold, exposing them to more indoor situations? Does it replicate more in the lungs and less in the gut? Does it show symptoms later, so people carry it unknowingly for longer? Does it mess with them neurologically, and make them feel more gregarious, or more lonely? Or more aggressive?
That would be amazing: If COVID-19 actually spawned more riots by directly messing with people's hormones, rather than the (already very plausible) frustration created by social distancing. My money's not on it, but it would be amazing.
Add up these selection pressures, and what you get is a target very much like that of the seasonal flu. And what do you know; the motley gang of viruses that cause the so-called "common cold" includes several coronaviruses. In other words, this exact scenario has probably already happened multiple times: A virus causing a dangerous pandemic doesn't go away, it gets forcefully evolved into just another agent for the "common cold".
Now there's a vaccine out. So far, the vaccine is thought to be effective against all strains of COVID-19, because all strains of COVID-19 use the same "spike protein" to gain access to cells. This is a gigantic inoculation on top of the regular flu-season inoculation, in the fight against what is essentially a monstrous, untamed incarnation of the flu -- in consequences, even if not in morphology. What are the chances that, the same way the flu does, COVID-19 will manage to stumble onto a different spike protein, and we'll need to retool our vaccines for it and re-apply them next year?
Now I have to soberly consider the prospect that we will put a boot down on the worst of COVID-19 ... and then we will need to do the same thing again for its slightly less fatal sequel one or two years later ... and so on, for five, or ten, or twenty years.
Picture the current social distancing standard, in slowly decreasing severity, not for one more year but for twenty. When will you consider it proper to throw away the mask, and sit down inside a restaurant, the way we all still picture restaurants in our heads? Given the enormous trouble we've all had sorting out the tested science from the noise, there will be a certain amount of personal, subjective choice at work. What's your yardstick? A death rate matching the flu? Less severe symptoms? The entire world immunized once? A yearly immunization in place, with no clear end? Total yearly deaths only twice that of the flu? (After about a year we are currently up to 2.2 million dead worldwide. The seasonal flu kills about 1/4th that many people.)
Or perhaps you will decide that none of this is adequate, and resolve to wear the mask and avoid indoor gatherings for as long as it takes. If there are enough of us doing that, social customs and city planning and architecture will all slowly bend in a new direction for decades. Theaters, concert halls, bathrooms, meeting rooms, restaurants, entire schools ... millions of them ... all will need to be reconfigured or perhaps just destroyed.
What if doing things that way could prevent ten million deaths, but human civilization collectively decides that one year of vaccine distribution is our triumphant moment, because we all damn well need to get back to work and back into classrooms and restaurants, and the next strain of COVID-19 is declared to be "only as bad as the flu" and folded into the pipeline of flu shot distribution ... and then a year later, a million more people have died?
I really hope one good vaccination hammer blow is enough to knock COVID-19 into the background. Otherwise, somewhere, we are all going to need to bring the science and the economics to bear, and draw an unpleasant line.
