WHO declares mpox epidemic public health emergency of international concern

[Externet]

Done.    

[CharonY]

1 hour ago, jimmydasaint said:

would infections of a locked down public not lead to more milder strains of the infectious agent/virus as the most aggressive strains would not be passed on because of the  mortality rates of the infected?

Not sure what the relationship between a lockdown and the virulence of a strain might be. Could You elaborate? If you mean that highly mortal diseases tend to get tempered over time, there is an argument for that, but not sure how it would relate to lockdowns. I should also note that this is generally only the case if mortality somehow limits spread. As an example, HIV without treatments had a high mortality rate, but disease onset was slow so it could spread widely.

1 hour ago, jimmydasaint said:

I am assuming that in a freely mixing population with more strains available due to movement of infected people between countries would lead to the possibility of import of more virulent viral/pathogen strains.

It is not necessarily a matter of mixing populations, but how many folks get infected. It is a bit of a roll of dice whether strains become more or less virulent. The main trend is usually towards higher infection rate (i.e. spread). Higher virulence can sometimes be a side effect, or it can lead to a reduction. For COVID-19, the Delta variant was probably more harmful than the original variant, but Omicron outcompeted it spreading more easily and occupying higher respiratory pathways, which led to lower mortality.

 

1 hour ago, jimmydasaint said:

However, surely natural herd immunity would serve to make most people more resistant to the imported more virulent strain due to cross reactivity of white blood cells with the antigens common to the first strain as well as the imported strain.

Again, not sure how your model works. If everyone is already infected a high rate there would be more immunity among survivors, yes. But obviously we then did not avoid the health burden at all. It is basically like solving hunger by letting enough folks starve so that the available food is sufficient.

 

Edit: upon re-reading, was the idea to explore how spread would work in a confined population? Generally speaking, in a full lockdown, spread would be curbed as infected individuals would not be able to spread the disease (regardless of virulence) outside of the population they are in contact with. Eventually, the disease would be eliminated. The issue is practically lockdowns are only limited there quite a few folks required to get things done.

[jimmydasaint]

Ok, I have time to clarify my nebulous thoughts and I will make them in bullet points for my own benefit:

1.IMO  In a population, more deadly strains of virus might be eliminated in favour of less deadly strains due to Natural Selection and high mortality rates of those infected with the more deadly strain. If aeroplane flights incoming and outgoing were severely curtailed, e.g. in a full lockdown scenario, the chance of introduction of new and deadlier forms should be also reduced. As a consequence, milder strains with milder symptoms should dominate the population. Even if the population was not isolated, less deadly forms of the virus should dominate as you correctly indicated. 

2. IMO if a population has been infected with a more virulent but less deadly form of the virus, the immune systems of those people who were infected should  be able to respond to a similar, but different form of the virus, because of common antigens between both. I know that health officials concentrated on what was a measurable correlate of infection - antibodies. However, these are transient measures of infection and the real immune response, IMO, is found in memory T and B lymphocytes which would focus the "seek and destroy" function of the immune response and would target parts of the viral antigen load which are invariant between strains during natural immunity. IMO natural immunity was not widely discussed by health officials at the time.

3. If mpox is deadly at the moment, during widespread infections amongst populations, IMO, the disease should gain virulence but milder and less deadly forms should be more prevalent. Natural immunity in the form of lymphocytes should be a mechanism of partial protection on further mutated strains arriving interminably. 

I think sort of clarifies what I was aiming at articulating and did not manage to write down in a cogent or lucid manner initially. 

[CharonY]

1. As I mentioned, the premise is a bit flawed. There is really only a negative selection on virulence if it fundamentally inhibits spread. This is not always the case. And in case of mpox, we see that the current strain is ha higher lethality, specifically because the original outbreak was not stamped out. It is also  not accurate to assume that more deadly strains have to arrive from elsewhere. The infected population are the reservoirs (plus non-humans, in case of zoonotic diseases) so it does not really matter if a lot of people are infected within or outside of a country. I think you use lockdown as in shutting down borders, rather than confining folks to their homes (the latter would eliminate spread as households would be isolated). 

2. I am still not sure what you mean here. I also think you might confuse "infectivity" with "virulence", when you say virulence. 

10 hours ago, jimmydasaint said:

more virulent but less deadly form

A more virulent form, by definition, causes more harm, which can include death. I think you mean to say that if folks are infected with more harmless strains they would also develop immunity, which is generally true and has always been a part of what happened to COVID-19. The issue is at the beginning of COVID-19 and also for mpox is that this form of immunity simply does not exist in the population. And now that a deadlier variant is circulating, hoping for natural immunity will have a higher death toll. This is why vaccination programs are getting more important now.

 

3. Again, as above the opposite is happening. Mpox is circulating and resulted in a deadlier strain, which clearly refutes your premise. Reduction of virulence (and again, more virulence means more harm) is generally only expected if death rates are high enough to curtail spread. Which basically means that many people have to die before we see more harmless variants see a reproductive benefit. And even that might not happen if a) its virulence is tied to its ability to infect or b) it is able to maximize its success in infections before the host dies (e.g. if it is infectious for long period of time before symptoms become severe). Syphilis is such a bug, which causes a very slow death. The safest way still remain vaccines, which is the equivalent of being infected with a  harmless strain, but without (or at least much less) the uncertainty of other sequelae.