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iayork t1_jd114s9 wrote

Possibly HIV might have become less virulent, but you absolutely have not detected that. What you are seeing is improved treatment of HIV.

There are a handful of ambiguous and marginal studies that hint that, in some regions and some populations, HIV might be becoming slightly less virulent. Again, you personally have not seen this because you don’t live in those areas and you personally don’t have the opportunity to test viral blood load in tens of thousands of stage-matched, strain-matched infected people.

> In support is evidence that SPVL, and hence virulence, has declined in some African HIV subtypes, even accounting for the use of antiviral therapy, and that this reflects a trade-off between virulence and transmissibility

The phylogenomics of evolving virus virulence

(The reference cited here is Blanquart F, et al. A transmission-virulence evolutionary trade-off explains attenuation of HIV-1 in Uganda. eLife. 2016;5:e20492.)

There’s a widely believed myth that viruses inevitably evolve to reduced virulence over time. In spite of the great confidence with which this is claimed, it is not true, there are many counterexamples, and there are 60 years worth of observation of theory (with math) demonstrating why it’s not true.

> For example, in the case of the second virus released as a biocontrol against European rabbits in Australia — rabbit haemorrhagic disease virus (RHDV) — there is evidence that virulence has increased through time … Similarly, experimental studies of plant RNA viruses have shown that high virulence does not necessarily impede host adaptation and, in the case of malaria, higher virulence was shown to provide the Plasmodium parasites with a competitive advantage within hosts.

>Theory therefore tells us that natural selection can increase or decrease pathogen virulence, depending on the particular combination between host, virus and environment

The phylogenomics of evolving virus virulence

So there’s no particular reason to expect HIV to evolve to reduced virulence.


JimmiRustle t1_jd13jcf wrote

I want to add that the outbreak in the 80s also caused a huge panic mainly because at first nobody knew what it was or how it spread.


supercalifragilism t1_jd4mpr9 wrote

Additionally, the rapid onset of negative health outcomes was because individuals had been HIV positive for much longer than a clinical definition for HIV positivity was developed. Treatment has improved, but for the early days of the AIDS epidemic there were people who had HIV for years before there was an official diagnosis, so the rate of time from diagnosis to death/disabling symptoms appeared shorter. Now HIV testing is part of established STI screenings, so there's (on average) less time for the virus to inhabit a person before diagnosis.


sciguy52 t1_jd5m30r wrote

I was an AIDS research scientist in the 80's. We had the lab we worked in without any infectious material in it (did the live virus work in another room). Anyway, one day we had a plumbing issue and the plumber did not want to come into the lab where all of us were working in. I was thinking "dude you think I would be in here if there was a risk of me getting infected?".


aphilsphan t1_jd5v5ex wrote

I was a grad student in the early 80s. There was a prof in our department who had been doing slow steady respectable RNA biochemistry work for 20 years. Not in HIV or even with whole viruses, with RNA viral enzymes. His work was barely funded, some semesters his 2 to 3 grad students taught, sometimes they’d get a break. By 1988 agencies leaving sacks of 50s on his doorstep. To his credit, this guy didn’t expand too much. He got a postdoc and better equipment and his students didn’t have to teach. It was fascinating to see that field go from backwater to front burner like that.


PlantLover1869 t1_jd3l4g4 wrote

Totally agree with what you’re saying about better treatment for HIV

I would also add there is better treatment for AIDS as well.

For example. One of the complications of AIDS can be PJP. Basically a weird organism that we generally never see causing a pneumonia elsewhere. If you were in the 80s and came in for a pneumonia. You would probably get something like cefotaxime plus clarithromycin. This wouldn’t treat PJP. Normally we treat PJP with high dose sulfamethoxazole and trimethoprim.

My point here is that even if someone doesn’t get treatment for HIV that when their immune system eventually becomes ravaged we know better what we are treating and how to treat it. At the start of the HIV/AIDS epidemic, we didn’t know what the virus was or what complications it caused. Now we know the pathway of aids and how better to treat it


freecain t1_jd4ju07 wrote

You also have to account for the issue that the first round of people getting Aids in the US and europe were largely part of the gay population at a time of extreme homophobia compounded by fear of this unknown disease. So - many were denied medical care or given extremely insufficient medical care, and the minimal treatments we had were delayed even further. Ie - if someone had the exact same disease today, without using any additional scientific breakthroughs or treatments from the last 50 years, just by not ostracizing the patient, you would see significantly better outcomes.

Then, there is the flip side that people would hide they had the disease as long as they could. Once they couldn't anymore, it was near the end - giving the impression of a sudden death after starting symptoms.


Cats_and-Crochet t1_jd1o28q wrote

And just to be clear, these viruses that became deadlier—they were racking up black death / smallpox-tours-the-americas fatality rates when first encountered, or were they only occasionally lethal to begin with? That'd be good to know when calculating trade-offs, and also whether the precise mutations that make the viruses deadlier were favored or disfavored depending on the mode of that virus' transmission...I'm thinking Ebola causing hemorrhaging which releases infected blood, for example. I could maybe see it being a benefit to a bug like HIV to cause a slightly more toned down version of fhis--something an otherwise healthy host can live with for years, concealing it from the people in his life


Coomb t1_jd3a5tt wrote

You can come up with just so evolutionary stories as to why a particular trait might or might not be adaptive, and therefore might or might not be selected for, for just about anything.

The specific example he gave of rabbit hemorrhagic fever virus is pretty much like a rabbit version of Ebola virus in terms of symptoms.

It was released in Australia in the mid-1990s, and rabbits have been co-evolving with it since then. This study captured wild rabbits in 2007 (meaning their ancestors had been subject to periodic outbreaks for over a decade and therefore could reasonably be anticipated to have evolved some amount of resistance, if resistance is possible), bred them a few times to get 80 rabbits, and then exposed those 80 rabbits to four different variants of the virus: the original isolate released in the mid-90s, and isolates collected in 2006, 2007, and 2009.

What they found was that, in these rabbits, the newest virus samples are considerably more deadly and also killed the rabbits considerably more quickly.

The original virus killed about 70% of all the rabbits they exposed to it, with an average survival time of about 120 +- 20 hours. The 2006 sample killed 85% with a survival time of 80 +- 16 hours, the 2007 killed 100% with a survival time of 45 +- 2.5 hours and the 2009 also killed 100% in 50 +- 3.5 hours.

Compared to the effects of the original virus on the original wild rabbit population, the authors cite an earlier study that found:

>Cooke and Berman (2000) showed that CAPM V-351 killed 22 of 24 unselected, nonresistant Australian wild rabbits, with survival times averaging 72.5 hr for orally inoculated rabbits (and BDC, pers comm.).

It seems clear that the wild rabbits did begin evolving resistance to the original strain of the virus, because although the original strain of the virus is still very deadly among wild rabbits, it's not quite as deadly. But it also seems clear that the viral evolution has caused it to maintain, at the very least, the same level of virulence as it had before it began coevolving, and perhaps an even higher virulence. There is certainly no evidence that after 30+ generations of rabbits the virus has reached a much less deadly equilibrium with the rabbits compared to its original virulence.

As far as just so stories go, I don't find any story that HIV would certainly naturally tend to become less virulent to be convincing. Even in completely untreated HIV, the latency time between infection and observable, behaviorally affecting significant illness is months to years.

So you have a disease that without modern medicine, looks like many other apparently random diseases that just occasionally kill people. After all, it isn't HIV that kills. It's opportunistic infections associated with AIDS. We have been able to identify a relatively small number of characteristic illnesses that pop up in modern society almost entirely among those who are immunosuppressed because of HIV, but that doesn't mean those illnesses would also be characteristic in a pre-modern society, and it doesn't mean anybody would have the widespread health surveillance to identify them.

In addition to that, the most common transmission method of an HIV infection is sex, and (both currently and historically) sex is something that humans like to engage in, and engage in quite frequently on average.

The point of all that is that, if you think HIV would evolve to become less virulent because virulence impedes transmission, you should consider that, other than the terminal phase, it doesn't impede transmission, and the number of possible transmission events between infection and symptomatic illness is, for many people, in the dozens to hundreds, or more. That means that even if it kills 100% of people in 5 years, it's never going to run out of people to kill until everybody's dead -- unless you have modern epidemiology that can identify there's some kind of infection and what the method of transmission is and what effective preventive methods are, and/or you can at least identify HIV infection as a specific illness and have effective medication to treat it.


sciguy52 t1_jd5q9qf wrote

So viruses need to be able to spread. If they are too deadly too quick, the infection burns out and the virus may die out with the people who died to quickly to spread it much. So take a hypothetical new virus that is 100% deadly on day three of infection and very contagious. People would die too fast to spread this around the world. So from the virus point of view, it can be deadly, but so deadly so fast to do what it wants to do which is spread itself around. Now viruses don't think of course, and if one existed like the one I made up above it would die out too quickly. So this is sort of where people started getting the incorrect belief that viruses mutate towards less lethality with time. No what happens is there is a selective pressure against a virus that is both very contagious and lethal in a short period of time. They certainly can exist, and perhaps they have in human history but they just died out before spreading too much. Now that is for a very contagious and quickly lethal virus. The virus did not mutate and become less lethal, it just didn't have the right "growth strategy" if you will that worked as far as spreading is concerned. So it may go extinct.

What if you were 100% lethal, but not for many years, say on average 8 years? Well now the lethality is not so much an issue as it allows many years for spread before it kills the person. In that scenario that selective pressure of "burning out" isn't there and it can continue to be lethal and spread around since it has time to spread. HIV is an example of that more or less. Also worth noting Over time it is certainly possible HIV could mutate to a less deadly virus but overall it has not really happened. And there really isn't a selective pressure for it to do so, but things like this can happen anyway over time, but not guaranteed.

Just as an aside, what would have happened with HIV if it happened in say 1900 before we understood viruses like this and really lacked the ability to do anything about it? It would potentially pass through a lot of the population ultimately killing those without some genetic protection that prevented lethality. But we humans have genetic diversity though, and there are some people out there with key mutations out there in one of the HIV receptors who seem resistant to HIV lethality. Over time those that had that key mutation would increasingly become more and more of the population as the others died, and the virus would become less lethal to the population due to the viruses selective pressure put on us humans. Then the virus might be able to infect some but not kill them, or not be able to infect them at all, and as a viral threat would become less and less a threat to human lives. It is thought this may have happened with other viruses throughout our long term evolutionary history. It is possible some viruses we get today that are not deadly to us may have been deadly in the long past but this selective pressure took place and the humans with some genetic resistance are the ones that survived, reproduced and make up more recent human populations. So in this scenario the virus didn't get less deadly, people essentially were selected for who did not succumb.