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Comment by paimapi | Hacker News Reader

this is more of a curiosity and not pushback but are there mechanistic reasons why viral mutations are subjected to tradeoffs in terms of lethality vs infectiousness? is it that the more lethal it is, the earlier it is that people become symptomatic (and thus are far more likely to isolate and/or be immobile)?

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The faster you kill your host, the less time you have to infect new hosts. Sure, you can loot the host to make a lot of new viruses, but when the host dies, they die too. Ideally, a virus "wants" to make the host live a long, gregarious life, touring the world and kissing babies. But that takes energy away from making more viral payload, so yeah, it's a tradeoff.

I don't think it's really a tradeoff and rather that Ebola is simply bad at its job. Why? Because it's primarily a bat virus (and it's basically asymptomatic in bats) that ended up where it doesn't belong and wreaks havoc because it hasn't learned to play nice.

In bats, it reproduces more slowly, doesn't kill the hosts, and thus the hosts live to spread it.

This is exactly the tradeoff I described.

> energy

That is almost irrelevant.

Our immune systems, and environments are mostly security-by-obscurity.

Viruses randomly mutate to find vulnerabilities.

Their biggest issue is finding solutions using a genetic optimisation algorithm.

Their biggest strength is that it is a massively parallel search. Think of 10^x monkeys bashing at all points in their reproduction (maybe 10^18 for peak covid in human hosts).

Viruses don't reproduce by mutation, they reproduce by getting the host to manufacture more copies of the virus, which takes resources (which ultimately come down to energy) away from the host.

The "monkeys" aren't trying huge numbers of variations, they are making huge numbers of identical copies with very rare (and usually non-functional) variations when they fail to copy exactly.

The survivorship bias is strong in you.

You're ignoring unsuccessful mutations... But those are the chaos monkeys that really matter!! "on the order of 10¹⁷–10¹⁹ individual nucleotide mutations per month". In part because infectious virions are far fewer than total viral RNA copies.

Which ends up with 2-3 mutations per month in the successful lineage. That's the "rare" number you're thinking of, but mutations are extremely common (as anyone with cancer finds out).

Your "energy" point is just plain wrong. You might carry 100ug of virus when infected - a tiny proportion of your weight. Total mass of virions in humanity at peak might have been 10kg.

See "The total number and mass of SARS-CoV-2 virions" https://pmc.ncbi.nlm.nih.gov/articles/PMC7685332/

I suspect you aren't reading well. I said:

> ...they are making huge numbers of identical copies with very rare (and usually non-functional) variations...

to which you replied:

> You're ignoring unsuccessful mutations...

You are also conflating absolute numbers with likelihoods; flipping two dozen heads in a row is a rare occurrence (1:2⁻²⁴). Saying that "if everyone on Earth tried it today we'd expect it to happen ~500 times" is not a counter argument.

You're also conflating the substitution rate (rate of mutation rate accumulation in the viral gene pool) with the frequency of copying errors (your "chaos monkeys" metaphor, to which I'm objecting).

Your objection to my statement that viral reproduction consumes resources from the host (which I shorthanded as "energy" since all cellular resources ultimately depend on this) is nonsensical. Who cares about the mass of the viruses?

That's like disputing the claim that "the vandals caused $3 million in property damage" by saying "but they only had $273.15 with them". It's completely irrelevant.

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