From COVID-era discussions (when virologists were briefly the stars of every talk show) I remember one explaining that it was less about fatality rates per se and more about the length of time you could carry the virus around and be nearly asymptomatic while still able to infect others.
I understand the jury is still out on whether a virus can be considered "alive" but, like us, it is capable of replicating itself and mutating. In that sense, it benefits from the same evolution strategies as more complex beings: a strain that gets its host very sick very quickly gets a lower chance to spread to a new host and multiply.
This creates an evolutionary advantage for strains of that virus that are less aggressive or at least develop the worst symptoms more slowly and more covertly.
Yeah. HIV is a good example of this. Without treatment, it is deadly pretty much 100% of the time. However, it takes a long time after the shut down of the immune system before a systematic infection takes over and kills you.
That allowed for a deadly disease that's somewhat hard to spread (mostly just through sex) to ultimately go on a rampage.
So without concern for the humans with HIV* there an argument to be made that treating symptoms without curing made it spread more?
*obviously, this is just hypothetical. It’s important to care about the life of those with HIV. No banish them all to something like a leper-colony. Although it explains the logic for those at the time they existed better than a religious one did.
HIV specifically targets the immune system. There's no way to just treat the symptoms.
The treatments we have now also decrease the risk of spread significantly.
It's a bit like the chickenpox. Once infected, you always have chickenpox ready to burst out in the future as shingles. But for the most part, it's dormant and you aren't infectious.
HIV treatment does the same. It doesn't clear your body of HIV, but it does decrease the HIV load to such low levels that it can be undetectable. That, in turn, decreases the likelihood you'll spread it.
HIV has only really been known for ~40 years. And for at least 10 to 15 of those years research into treatment was limited and stigmatized as it was considered a "gay disease".
The modern treatment regime was developed around 2010. That is, about 15 years.
I'd argue that with the timeline of the disease that's not recent. What's become more recent is the mass availability of treatment and the significantly reduced cost of treatment.
There's a significant difference in the risk and mechanisms of transmission between these two viruses. The modern effective reproductive number for HIV is less than 1, about 30-50% lower than ebola in similar subsaharan countries [1][2]. You can get ebola from contact with an infected person's sweat during the active phase [3]. You can get it from their semen years after they have apparently recovered [4]. We don't have treatments that work in this longer term. The drugs that we do have are used during the active infection period to reduce the probability of death during the crisis. Folks are working on reducing the longer term infectiousness but it's a ways off yet [5]. We also don't have pre- or post-exposure prophylactic treatments for the medical workers who are at the highest risk of infection or the family members--the most common transmission mechanisms for ebola are home caregiving and contact with traditional burial practices. In this context of containing an active outbreak, quarantine is mostly helpful in reducing pressure on the medical system for a short term.
Compare this with HIV, which can be rendered untransmittable with modern treatments, which is primarily a sexually transmitted disease, which has pre- and post-exposure treatments. It's simply not very efficient/effective to exile millions of people with a lifelong latent infection and little risk of transmission.
The instinct towards ostracism of those who are perceived as unclean is some pretty primordial lizard brain shit which was a great rule of thumb two thousand years ago, along with wearing garments made of only one kind of material. It's actually actively harmful to the process of stopping infection. It leads to fear, distrust, and reduced reporting, hindering the medical system's ability to reach the people who most need to be reached, and encouraging the spread of superstition and suspicion of pre- and post-exposure treatments. In both diseases, the actual infection risk is modest compared to an airborne virus like COVID.
>I understand the jury is still out on whether a virus can be considered "alive"
I remember way back in med school in the mid-70s our infectious disease professor asking this same question, in a philosophical as much as a mechanistic sense.
Here is the fun thing to think about: If viruses aren't alive, neither are men. Men, too, lack the biological means of reproduction. On the other hand, parthenogenesis may even rarely happen in female humans.
I don't think it's just fatality rate, but also how long it takes to kill you. HIV is a great example of a disease that (untreated) has near 100% mortality rate, but can spread because it takes years to kill you.
The real issue with HIV is that you can easily spread it before being symptomatic, so far we haven’t seen hantavirus spreading before folks become symptomatic. The strain that spreads through humans has been active in south America for a while as well and hasn’t really gone anywhere yet.
Plague, Inc (an iOS game where you control the parameters of a pandemic and try to get a 100% infection rate) will give you a really good feel for the math behind this.
The most successful strategy is to make a virus that spreads fast, with few visible symptoms until the late stages of the disease. A deadly virus, early will just cause borders to be locked and the international research community to swarm on a cure.
If AIDS were airborne, I think we'de have a fraction of the billions currently living today. It takes a while for symptoms to show up, there is still no real cure, and drugs to keep it supressed took many years to develop.
"It depends" is usually a safe (if not always helpful) answer. The older idea was that viruses always evolve to be less virulent/deadly, but that didn't match observations. The newer idea is simply that of a virulence-transmission trade-off. But there are various assumptions behind both ideas, and not all viruses follow those assumptions, so.. it depends. A decent review: https://pmc.ncbi.nlm.nih.gov/articles/PMC10066022/
Is that like a general rule, or pure bunk? (I'd probably assume the answer 'depends').