Viral load - can someone explain?

[OverUnderSidewaysDown]

Can someone with expertise explain viral load? I used to understand it as meaning how much virus an individual was carrying and shedding , i.e. how infectious they were to other people. But in recent days I've heard it described as meaning how much virus a person is exposed to, and used as an explanation for why doctors and nurses are getting the virus more than other people.
Which is correct? A doctor could catch it from just one patient, but if they treat one hundred patients does their susceptibility increase?

Yes. The more you are exposed the more likely you are to get it and the worse your symptoms might be.

I understand it as if you lick public doorhandles and several infected people sneeze directly onto you or a lot of sustained contact with infected people and no PEE vs if your finger touches something with a few particles on it and then an hour later you touch your eye... along those lines

Sorry though Im not someone with expertise so Im sure an expert will confirm (or say Im wrong!)

PPE even sorry good lord

Yes I think they’re saying it’s the reason why people who catch it from a household member are likely to have worse symptoms than if you catch it from a passerby who coughs or whatever.

I think for illnesses like HIV and strains of hepatitis the aim is to reduce viral load which suggests to me that more exposure to a virus would make it harder to reduce.

There was also a report out today from Iceland that they’ve identified multiple strains with one patient having two. No scientific/medical background but I imagine that’s pretty hard for the body to cope with.

Viral load is the amount of virus in your body. A high viral load usually means you are both sicker and more contagious. If you are exposed to corona 100 x you have 100 x as much virus in your system so instead of 1 lot of covid 19 attacking you you have 100 lots of covid 19 attacking you. Another thing that can affect viral load is how much the virus multiplies, so if you have reduced immunity the virus will be able to multiply more quickly so you Could get more sick and faster than somebody with better immunity

It's the amount of virus in your blood. en.wikipedia.org/wiki/Viral_load

Right so I have a biology degree, my knowledge may be a bit rusty but as far as im aware.

Viral load in a virus such as HIV refers to how much virus is in the blood. A higher viral load means the virus has replicated considerably in the blood and thus much more of the virus is present in blood, breast milk, seamen etc

With Sars-Cov-2 the virus that causes Covid-19 a high viral load would mean the virus is at their most infectious because the virus is at its peak (however they likely feel most ill at this point so may end up in bed at this point thus not infecting wider public). VIral load would reduce after the body learns how to fight coronavirus.

If you have built up some previous immunity to a similar virus/same virus and your immune system is in good shape then it's like your immune system are a specialised target team who are better at attacking the virus therefore you beat it more easily. Eg. Seasonal flu even if we haven't had the strain if our immune system is good we can get the virus in check pretty quickly, UNLESS our immune system is weakened in which case our white blood cells stop being so clever. The flu vaccine gets out bodies booted up again with a refresher for our flu fighting target team which is why even if we have the wrong strain we will likely get it less badly. With covid 19 we are a naive population, which means we are all exposed for the first time. But if we are only exposed once and otherwise healthy we should be fine. If we are only exposed once but have a compromised immune system we could end up unable to fight the virus, viral load getting too high and potentially very sick/dying. If we are exposed multiple times then and healthy it can still be deadly because no matter how good our white blood cells they are outnumbered. Normally the virus is at a disadvantage, this time we are at the disadvantage and the only way to reduce the risk is to not get the virus at all, get the virus but not badly (low viral load) or to wait until there is a vaccine so that our immune systems have been "trained" to fight the virus more effectively. Herd immunity works on the basis that if most people have had it but not badly then they will fight it off more effectively if exposed and less people will have it at a less high viral load therefore less exposure means it's less deadly.

But herd immunity has only been proven in practice with vaccination programs not majority infection of a virus. So we need to reduce exposure. Even if we get the virus we are better off if we get it from less exposures and expose less people to it and when the viral load is lowest. So whilst lockdown measures and social isolation time scales are not perfect they prevent large scale exposure of the virus at its highest potency, essentially

thank you all , I think I'm understanding it now. Lots of virus in the body= more dangerous to other people but also more dangerous to the host.

So doctors would be more vulnerable - but also if infected could be more dangerous to other people (except they would be wearing masks etc).

@HerstoryInTheMaking

Yes so with a low enough viral load HIV is no longer contagious to others even though the person the self is still HIV positive. Which is why they are trialling HIV meds and hepatitis (and malaria) on covid 19 to see if we can use them in a similar way with this

@OverUnderSidewaysDown

Yes at this point it's believed the mask protects other people more than it protects the wearer but even if both doctor and patient have covid 19 they still need to avoid cross infecting one another. And even though they are exposed at work it's paramount they are not also exposed in lots of other environments. So even if they spend all day with inadequate PPE caring for covid 19 patients they still are at less risk if they don't have to visit packed supermarkets, walk down busy streets and sit on crammed tube trains. So we protect our front line health care workers by staying at home even if they end up with the virus they could well get it less badly AND will not have a queue for a ventilator. And if we get it we are better at home self isolating than giving It to all our family members, because each Person who gets it tends to get it worse than the last.

The answers above are really useful, because I think a lot of us were brought up to believe that "just one germ" could give you a particular illness. I don't think a lot of people know what has been explained above, that you might not get it from one germ but are more likely to get it, and be more ill, if you are exposed to multiple germs.
I think this is why people have been so careless about self -isolating. I've certainly heard people say, why ban football matches, you could just as easily get it from someone standing next to you in a shop. - but that's not true. The explanations from posters here should be explained to the public at large IMHO.

We are better at catching it from touching our face accidentally once than repeated exposure from general sloppy hand washing practices, too. It's about minimising the risk of exposure and also minimising the LEVEL of exposure if we cannot entirely mitigate risk

really helpful AnotherMurkyDay, and others - thank you.

I thought it was basically that if your initial exposure is to a small amount of virus, your immune system can start making antibodies and the various defence mechanisms have a chance of dealing with it quickly.

Whereas if you get exposed to a lot at once, there's too much to deal with.

What about if you are incubating in the home, without showing symptoms
Would this mean you are dangerous to your family?

anothermurkyday does this mean it's possible for a household to re-infect each other, if person 1 has it mildly, person 2 has it worse is there a risk person 1 could get it again? Or is person 1 more likely to be immune?

@7Days usually if you don't have symptoms it means that you do not have the virus or that you have it but your viral load is low. Once you are symptomatic the virus load is higher therefore more contagious and you should self isolate so much as possible, so if you cannot completely self isolate within your household then you try to limit risk as much as possible through hand washing, keeping a distance etc. Obviously this is hard if not impossible to do if you have small children, are a lone parent, live in a very small space, etc. But if you are in a couple and are breastfeeding a baby but your DH/P can keep the toddler away then that's better than all deciding nows the time to start bed sharing, for example

Thank you MurkyDay.

@tempestterra

At the moment because covid 19 is so new nobody knows exactly what happens with immunity yet, especially long term, but there is evidence that in the short term at least once you have recovered from the illness most people seem to have short term immunity at least. So if person 1 gives it to person 2 that should be the end. If there are three people though, then person 1 can give it to person 2 but both can be passing it to person 3 simultaneously meaning person 3 could be at risk of a worse version. So if person 1 is a front line health care worker, even if they give it to person 2, person 2 is still better being the only one looking after person 3 (if person 3 can be kept entirely separate from person 1) because they should get it at a lower viral load. At least that's a theory emerging, it's early days to know these things for sure. Certainly staying at home for the whole of or as much of the infectious Period and being in contact with as few people as possible, be that inside or outside the home, is the best way to minimise the risk to others

It's the reason why even though front line workers and their children are at higher risk of exposure, that doesn't mean them all spending a lot of time with other frontline workers and their children. And why just because you're neighbour also doesn't have symptoms doesn't mean they should be coming round for a cuppa

Sorry spell check destroyed my last comment. It's why frontline workers shouldn't all be socialising with other front line workers and even though their children might be exposed they should still be kept away from other children as much as possible (so only using schools as absolutely necessary). Also why even if you and your neighbour both DO have symptoms, you shouldn't be going round to each other's houses for a cuppa