/ Viral load

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girlymonkey 27 Mar 2020

I found this article interesting. This explains why 2m distance is important. It also makes me think that the rest of the country probably won't have the same percentage of severe cases as London due to London's density of population and the underground. 

https://www.sciencemediacentre.org/expert-reaction-to-questions-about-covid-19-and-viral-load/

Thugitty Jugitty 27 Mar 2020
In reply to girlymonkey:

Thanks, that’s interesting.

skog 27 Mar 2020
In reply to girlymonkey:

Yeah - my wife has type 1 diabetes and is a physio; she's not being deployed to the wards due to the higher risk from this, so staying second-line support instead.

She could still get a big infecting dose if a sick patient coughs in her face, though - and their team don't have masks, just gloves and aprons.

The best scenario for us is probably something like me picking it up in the supermarket and spreading it round the household while I'm not producing too much virus, so she's likelier to get it milder.

It's a worry.

girlymonkey 27 Mar 2020
In reply to skog:

Yes, it makes you think more about where you go etc. 

We are currently isolating due to my brother in law arriving from Mexico at the weekend via Miami and London. We weren't sure how much to distance him from us in the house, figuring that if one gets it, we will likely all get it anyway. 

We have kept good distancing and kept him using a separate bathroom and we are cooking. Seems like this is worth the hassle, reading this. He is likely to have had a bigger viral load than we have if he has picked it up on his travels and keeping distances should mean that if any of us have it, the others should be less severe with it if the distance is greater.

skog 27 Mar 2020
In reply to girlymonkey:

Hope it goes well for you all.

girlymonkey 27 Mar 2020
In reply to girlymonkey:

Thanks. None of us have any reason to think that it would be highly dangerous for us to get it, but that's no reason to be complacent! We see our distancing more being for others than ourselves.

I hope your wife manages to keep safe and gets the PPE that she needs

Post edited at 07:48
aln 27 Mar 2020
In reply to girlymonkey:

Thanks for that.

Gordon Stainforth 27 Mar 2020
In reply to girlymonkey:

Many thanks for this. I have never seen this detail before, nor indeed heard of the 'viral load' before. I had mistakenly assumed that you simply needed one 'virus' (viral particle) to catch the disease, and that was it. I had no idea that it came in 'doses', as it were.

wintertree 27 Mar 2020
In reply to Gordon Stainforth:

> I had no idea that it came in 'doses', as it were.

This was one of the warning signs - the young doctor in China who died early on.  

lorentz 27 Mar 2020
In reply to girlymonkey:

Ah. The London Underground. Transport for London (TfL) decided to start running a reduced tube service closing stations meaning that the key workers all had to pack into carriages and along platforms like a regular Monday rush hour (along with builders who are apparently too vital to the economy to be told to stay at home.)

Meaning of course that loads of NHS staff and those that are vital to running the infrastructure have likely been exposed to a hefty dose of the virus on their way to and from work, instead of sitting several feet away from each other as they had been right up to the point  that TfL started reducing the underground service. As a result many NHS staff are now in self isolation having had symptoms, just as the virus starts to bite.

And of course these vital workers are still awaiting the testing kits to see if they actually have had the virus or not can return to work (and may have some immunity.)

Nice joined-up thinking by TfL.

Post edited at 09:11
girlymonkey 27 Mar 2020
In reply to lorentz:

That's horrific! 

Yes, I think those of us who have often bemoaned the lack of public transport elsewhere in the country might do better in this time because of the lack of it! Very thankful that my bike is my main transport!

girlymonkey 27 Mar 2020
In reply to Gordon Stainforth:

It was new to me too. I looked it up after a comment I read on someone's Facebook post. 

Nice to have the time to look into facts about random comments! I have looked up a few interesting things on the back of comments people have made this week!

oldie 27 Mar 2020
In reply to Gordon Stainforth:

> I had mistakenly assumed that you simply needed one 'virus' (viral particle) to catch the disease, and that was it. I had no idea that it came in 'doses', as it were. <

My interpretation, though I'm simply a layman, is that you can get a viral disease from one virion, at least in theory. Once a single virion enters a cell it is invulnerable and exists simply as nucleic acid which "hijacks" the cell to produce huge numbers of new virions. These are released into the body (I presume generally through cell death and rupture). However if, say, a thousand viral particles (virions) infect a thousand cells then the initial virion release into the body will be a thousand times greater. Each virion can then infect a new cell and the process is repeated.

Thus the body stands a very good chance of either eliminating a single virion before it infects, or of combating the much smaller viral load resulting from the death of only a single infected cell andof the immune system developing an ability to cope with the disease before its effects become too drastic.

I've posted this largely so I can be corrected and learn those more knowledgeable.

Michael Hood 27 Mar 2020
In reply to oldie:

That was sort of my understanding. I'd realised it to some extent when hearing about the otherwise healthy young medical staff that had succumbed, but then more recent reading had confirmed it (and further confirmed by the OP's link above).

I feel this was a missed communication opportunity from the government, social distancing is a weapon with "two strings to its bow" so to speak; 1. less likely to catch the virus, 2. increase chances of lower viral load if do catch the virus which increases the chances of only having mild illness.

Robert Durran 27 Mar 2020
In reply to girlymonkey:

I'd been wondering about this.

So last night I watched QT (so much better without the baying live audience!) and they were all sitting the regulation 2m apart for an hour. Presumably the risk of transmission if I'm out for a walk and I pass someone coming the other way on the path and I might in fact be closer than 2m for about half a second is far lower.

Hardonicus 27 Mar 2020
In reply to oldie:

I assume it is exactly the same maths as that which drives the need for self-isolation. The growth rate of virions is exponential so the initial seeding number at the initial infection has a major impact on the scale-up rate of the virus. Too fast and the immune system is overwhelmed due a limits in its reaction time.

HansStuttgart 27 Mar 2020
In reply to girlymonkey:

Interesting, raises the question whether a low virus load that is not strong enough to cause disease symptoms is enough to start antibody production.

girlymonkey 27 Mar 2020
In reply to HansStuttgart:

My guess (based on no scientific education what so ever!) is that a small amount will, as that is how vaccines work. How small an amount though?

Robert Durran 27 Mar 2020
In reply to Hardonicus:

> I assume it is exactly the same maths as that which drives the need for self-isolation. The growth rate of virions is exponential so the initial seeding number at the initial infection has a major impact on the scale-up rate of the virus. Too fast and the immune system is overwhelmed due a limits in its reaction time.

I don't see that that follows; the scale up rate would be the same no matter the initial dose. All I can think is that a low initial dose gives a brief window for the immune system to get a grip on it and prevent it going exponential. But I am speculating - we need someone who knows about this stuff.

1
DancingOnRock 27 Mar 2020
In reply to lorentz:

Well, you don’t know that they were hefty doses. 
 

The line from TFL is that their trains and stations are driven and staffed by human beings who are also at risk from the virus and live in households with people at risk from the virus and also self isolating. Trains don’t drive themselves yet. 
 

How about a bit of sensible thinking. 

3
Mark Edwards 27 Mar 2020
In reply to girlymonkey:

Perhaps the viral load theory partly explains the suspicion that people were catching CV here in February and why it wasn’t causing the deaths we are seeing now due to it being far more diffuse.

DancingOnRock 27 Mar 2020
In reply to Robert Durran:

Yes. Close contact is considered 2m for 15minutes. 15 minutes is difficult for humans to keep track and someone might cough in that time anyway so best make that a short as possible. 

Yanis Nayu 27 Mar 2020
In reply to Gordon Stainforth:

It’s the same I guess as the ‘infective dose’ with food poisoning - with some bacteria you’ll need to ingest a million to make you ill, and others only 10. 

David Myatt 27 Mar 2020
In reply to girlymonkey:

Good article, thanks.

skog 27 Mar 2020
In reply to Mark Edwards:

> Perhaps the viral load theory

It's not so much a theory as a well known effect that the infecting dose of many pathogens can affect outcomes from the associated illnesses; it's by no means unique to this disease.

It's part of why staff in wards (and care homes) can be at such high risk and why more vulnerable staff such as my wife are being kept to roles where exposure is hopefully lower.

lorentz 27 Mar 2020
In reply to DancingOnRock:

Drivers sit in separated booths. Most of the station staff sit behind glass too. 

Dave Garnett 27 Mar 2020
In reply to girlymonkey:

> My guess (based on no scientific education what so ever!) is that a small amount will, as that is how vaccines work. How small an amount though?

That's a hard question and it depends on how intrinsically antigenic the pathogen is.  Just how obvious, chemically, is it to your immune system - is it mostly small, soluble molecules? Is it chunks of poorly soluble stuff that macrophages like to eat? How and where it enters and develops (is it growing in a relatively immunologically inaccessible part of your body, for instance? TB bacilli aren't that exciting as far as your immune system is concerned, and tend to get walled off rather than dealt with). Is it a bacterium (which are usually tagged by antibodies directly and attacked by a variety of immune cells) or a virus (in which case the main defence strategy is to enable cytotoxic T cells to recognise infected cells and kill them)? 

Some of it is genetically determined by your tissue type too, so that there will be some specific peptides your immune system doesn't see well and others it might see too easily (like your own thyroid antigens, for instance). 

That said, if you think of the tiny amounts of allergens that are capable of sensitising your skin (like traces of almost insoluble metallic nickel in cheap jewellery) your immune system is pretty good at spotting something 'non-you' where it shouldn't be.  And there are ways of manipulating an antigen to maximise the way it stimulates the immune system (from simple chemical treatment and adding irritating adjuvants to sophisticated gene editing to get cells to react to cancer antigens)

The way in which virally-infected cells present bits of viral protein on their surface so that the right type T cells will get excited about it, or  bacteria are attacked, broken up and fragments of their proteins then presented to one of other sorts of T cells in order to kick off antibody production, is fascinating if you are the right kind of geek.  Try looking up MacFarlane Burnet and 'clonal selection', for instance- and it turned out that was only half the story!       

Dave Garnett 27 Mar 2020
In reply to Yanis Nayu:

> It’s the same I guess as the ‘infective dose’ with food poisoning - with some bacteria you’ll need to ingest a million to make you ill, and others only 10. 

Imagine that you eat a single nasty bacterium that makes some exotoxin and that it divides every half an hour or so.  The exotoxin needs to be at a specific concentration before it makes you ill.  It's a race between the replication rate of the bug and the transit time before it next sees daylight.  The bigger the dose you eat, the more likely you'll fall ill.

It's complicated by the fact the bug might cheat by attaching itself to your gut wall (which is basically why some E. coli are pathogenic) but it's alway going to be worse if the original bacterial (or viral) load is higher.  Even if it's something exceptionally horrible like rabies virus, the larger the dose, the less time there is to do something about it and the less likely that is to work.

oldie 27 Mar 2020
In reply to Robert Durran:

> I don't see that that follows; the scale up rate would be the same no matter the initial dose. All I can think is that a low initial dose gives a brief window for the immune system to get a grip on it and prevent it going exponential. But I am speculating - we need someone who knows about this stuff. ,

Well if the rate of new virus particles per unit time for 1 initially infecting virion  was compared with the rate for 1000 initial virions, surely after a given number of "generations" of cell had been infected there would always be 1000 times the number of virions in the latter case, until some sort of saturation was reached eg immune system action or death of host body. Again total speculation on my part.

Toerag 27 Mar 2020
In reply to girlymonkey:

I use the analogy that it takes the body x days to work out how do deal with the problem, and y days to create enough antibodies / white blood cells to deal with it.  The clock starts when you first get infected, no matter how many virions infect you.  If you get infected by 1 virion by the time it's replicated enough to be a problem times x & y have elapsed and you get better.  If you get infected by 1000 virions at once they've multiplied into too many for your body to handle before it's had a chance to complete times x&y and you get pneumonia and die.

Or it's like you're in a boat and a madman pokes a hole in the bottom - it takes time for you to find a plug and bung the hole up. If he bangs 10 holes at once you sink because you can bung them up in time.

Post edited at 12:02
Robert Durran 27 Mar 2020
In reply to oldie:

> Well if the rate of new virus particles per unit time for 1 initially infecting virion  was compared with the rate for 1000 initial virions, surely after a given number of "generations" of cell had been infected there would always be 1000 times the number of virions in the latter case, until some sort of saturation was reached eg immune system action or death of host body. Again total speculation on my part.

By "scale up rate" I took it to mean the doubling rate. My point was that an initial lower number of particles may just buy time for the immune system to get a grip on it. Suppose the doubling time is 1 hr (I've absolutely no idea whether this is realistic, but that doesn't affect my point) , then, because 2^10 is roughly 1000, after 10 hours you will have caught up with someone with an initial load 1000 times greater - your immune system has 10 extra hours to tackle it.

oldie 27 Mar 2020
In reply to Robert Durran:

Yes, I think I was sort of agreeing with that, but it all depends on how long before the immune response kicks in. Also if it takes a fair amount of time for a cell to make new virions, rupture and release virions (if that is the mechanism) then that might give the immune system more time to get going (probably need the first "generation" of infected cells to rupture to produce antigen first).

Usual probable bull...t warning.

freeflyer 27 Mar 2020
In reply to girlymonkey:

So the question arises - how to get an appropriate viral load and immunity with minimal symptoms, given the lack of any medical alternatives.

Seeing as the PM and PoW and others seem to be ok, maybe we should all nip down the supermarket and shakes everyone's hand.

DancingOnRock 27 Mar 2020
In reply to lorentz:

All the time? Are you sure? I think they probably travel home at night time, probably on the tube. 

krikoman 27 Mar 2020
In reply to freeflyer:

> Seeing as the PM and PoW and others seem to be ok, maybe we should all nip down the supermarket and shakes everyone's hand.

If they're telling the truth

phizz4 27 Mar 2020
In reply to lorentz:

I'm not trying to excuse TFL's approach but, from converstions with business people locally there are high levels of absentiesm amongst many workforces. TLF are short of staff, so there are many train and bus cancellations. Some of this shortage is due to genuine self-isolation reasons, but feedback I'm getting is that shirkers are also using the situation to get themselves a paid break from work.

4
Roadrunner6 27 Mar 2020
In reply to girlymonkey:

Yeah and why areas like Italy, old towns are hit so badly.

bouldery bits 27 Mar 2020
In reply to girlymonkey:

So....

(Remembering that I am a well known idiot and am very tired from trying to keep 15 7-11 year olds, who really did not wish to be in school, entertained this week.)

Why not give everyone a tiny tiny dose. Then get them to isolate. Then they'll be all antibodied up? 

Obviously, there would be risk and we'd have to isolate ourselves pretty firmly afterwards. However, by controlling the viral load can we not minimise the symptoms and speed up immunity?

Post edited at 20:53
Dave Garnett 27 Mar 2020
In reply to bouldery bits:

> Why not give everyone a tiny tiny dose. Then get them to isolate. Then they'll be all antibodied up? 

Better still why not give everyone a tiny dose of some killed virus so they prime their immune system without the risk of infection?  Or give them just the bits of the virus you need to provide immunity?

Or vaccination as it’s sometimes called.

Ardo 27 Mar 2020
In reply to girlymonkey:

Not read the article yet, but will do when less wine consumed and thank you, so far, to respondents who haven't turned this into yet another "you're an idiot, we're all going to die/we're all going to be fine idiot" thread. (So please can we keep it that way till the wine toxins have abated ;-).

girlymonkey 27 Mar 2020
In reply to bouldery bits:

Is that not what a vaccine is? 

I guess getting a mild dose with a small viral load is still all relative depending on the person. So presumably in one person a large viral load might cause a bad enough reaction to keep them in bed for a couple of days and a small one might leave them asymptomatic whereas a large load might kill another and a small does only puts them in bed for 2 week? (I'm guessing!)

girlymonkey 27 Mar 2020
In reply to Ardo:

> Not read the article yet, but will do when less wine consumed and thank you, so far, to respondents who haven't turned this into yet another "you're an idiot, we're all going to die/we're all going to be fine idiot" thread. (So please can we keep it that way till the wine toxins have abated ;-).

Do I win a prize?!

bouldery bits 27 Mar 2020
In reply to Dave Garnett:

> Better still why not give everyone a tiny dose of some killed virus so they prime their immune system without the risk of infection?  Or give them just the bits of the virus you need to provide immunity?

> Or vaccination as it’s sometimes called.

My understanding was that producing a vaccine was becoming problematic and had a huge timescale by which point it might be a bit late. So would this be quicker?

Did a quick read tho and found that the issues are regulatory rather than a physical barrier. So, yeah. Let's just bang out a proper vaccine. 

bouldery bits 27 Mar 2020
In reply to girlymonkey:

This is a point. How big a dose do you need?

Ardo 27 Mar 2020
In reply to girlymonkey:

My sincere gratitude enough? :-

DancingOnRock 27 Mar 2020
In reply to bouldery bits:

Just the one to infect a cell. It’s basically playing the lottery. The more tickets you buy the more likely you win. One ticket and you can buy some beers, too many tickets and you have too much and can’t get rid of it. 

girlymonkey 27 Mar 2020
In reply to Ardo:

Gratitude is definitely something to be valued! Prize accepted 😊

bouldery bits 28 Mar 2020
In reply to DancingOnRock:

> Just the one to infect a cell. It’s basically playing the lottery. The more tickets you buy the more likely you win. One ticket and you can buy some beers, too many tickets and you have too much and can’t get rid of it. 

Thanks for this clarification. Very very interesting stuff.

bouldery bits 28 Mar 2020
In reply to girlymonkey:

Cheers GM. Really interesting and useful science. Hope you and yours are staying safe!

Cheers,

BB

girlymonkey 28 Mar 2020
In reply to bouldery bits:

Thanks BB. It was totally new to me when I read it and thought it might help others to think too about how and why we are doing things.

Yep, we are staying safe and well. Due to a foreign arrival in our house last weekend we are all staying at home other than going out for exercise. Thankfully the weather has been largely good for cycling etc 😊

Hope you are also staying safe.

Wiley Coyote2 28 Mar 2020
In reply to girlymonkey:

This has been a very interesting and, as someone else said, very civilised thread so I wonder if  if anyone can explain something that has been puzzling me.

I've been keeping an eye on the stats for cases around my village, which sits close to three reporting areas. North Yorkshire, a largely rural county,  currently has 75 cases in a population of 614k, Lancashire, slightly more urban but with big rural swathes is 167 cases in 1.2m pop (so more or less similar per head). Bradford on the other hand, which is a densely populated city where I would expect the virus to spread more easily,  has  only 37 cases in a population of 537k. It seems counter-intuitive  that the densely-packed city should be running at about half the rate of the two more sparsely-populated shires. Can anyone shed any light on why this is happening?

DancingOnRock 28 Mar 2020
In reply to Wiley Coyote2:

Entirely down to people’s behaviour and how big their social groups are. All it takes is one person crammed into a crowded local pub and you could infect the whole village pretty quickly. So you get hotspots rather than large wide area infections. Plus it takes 14+ days in some cases for people to seek medical attention, so it could just be early days. 

Wiley Coyote2 28 Mar 2020
In reply to DancingOnRock:

That's an interesting theory. Bradford has a substantial Muslim population who, I would imagine are not crowding into pubs. On the other hand, they do tend to mingle in large extended family groups. Which is more likely to lead to increased infection I've no idea.

girlymonkey 28 Mar 2020
In reply to Wiley Coyote2:

I wonder whether these large extended family groups don't socialise as much outside of their grouping? This could mean cases more contained? 

Or maybe their lack of pub going etc leads them to be generally healthier than the rest of the population so the virus may be spreading there but most cases not so bad as to require hospital admission?

DancingOnRock 28 Mar 2020

I think it’s probably just luck at the moment. It’s not very widespread outside London. 1/3 of the deaths are in London alone.

Hardonicus 28 Mar 2020
In reply to Wiley Coyote2:They might not congregate in pubs, but a very large number cram in mosques on a weekly basis for Friday prayers!


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