‘Badder’ isnt ‘Better’: Does evolution favor a deadlier HIV?

Though this paper (the one I began talking about before a holiday break) is the reason for this post, this post is also an opportunity to address a question I have gotten a lot over the years:

Is HIV evolving to be more deadly?

The short answer would be: No, it doesnt appear to be. Scientists have battled 'new' HIV variants vs 'old' HIV variants, and the younger variants are no more aggressive than the older versions.

Replicative fitness of historical and recent HIV-1 isolates suggests HIV-1 attenuation over time

The findings of this paper are, unquestionably, limited. They only looked in a small subset of patients infected with Subtype B viruses, and the time-frame was 1986–1989 for the 'old' viruses (samples from like 1898 would be ideal, but they dont exist) to 2002–2003 for the 'new' viruses (over ten years old today). But their findings were exactly what I would expect.

Look at SIV.

SIV has been infecting non-human primates a lot longer than HIV has been infecting humans, and non-human primates dont have condoms or antiretrovirals or bone marrow transplants... SIV has evolved the way it 'wants' to evolve naturally in those hosts. If SIV is totally going to get more deadly over time, SUPER DEADLY SIV/AIDS, where are the acutely lethal SIVs? (other than SIV-PBJ which was accidentally evolved in a laboratory setting)

SUPER DEADLY SIV/AIDS is *not* how SIV has evolved in other primates.

Certainly, SIV does have a negative impact on the life-span and reproductive capabilities of, for example, wild chimpanzees. But then again, SIV doesnt have a major effect on sooty mangabeys. But there are definitely no naturally evolved acutely lethal SIVs.

And looking at HIV/SIVs life-cycle, why would we expect it to 'want' to be acutely lethal, evolutionarily?

An acutely lethal HIV means you die in a matter of days/weeks. New viruses would have few/no opportunities to pass to a new host. A dead host would be a dead end for this kind of virus.

A chronic HIV that does not cause much medical harm would allow the host to stay alive, casually transmitting virus to sexual partners, offspring, etc. over an extended period of time. Years, decades. Lots of new hosts with lots of time and opportunities to infect more hosts. *That* makes more sense to me.

This isnt to say that acutely lethal HIV variants could not ever evolve (see SIV-PBJ). They could. But I think they would be fleeting. They would emerge and burn out.


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