4 ms·

> Usually viruses become more transmissible and less lethal in response to rational behavior in their hosts--but humans are proving we're not rational. I was u

> Usually viruses become more transmissible and less lethal in response to rational behavior in their hosts--but humans are proving we're not rational. I was under the impression viruses became less lethal because if they became more, they'd kill off their hosts and be less likely to spread. There's a chance you get some super virus that becomes both more transmissible and lethal, but that is very rare (from what I can see).

AbortedLaunch 5y ago
It depends. It’s hard to model and even think about the selection pressures accurately. West Nile virus showed a marked increase in virulence in corvids recently as did rabbit hemorrhagic disease. And let’s not forget about Mareks disease, where a non-sterilizing vaccine is thought to have contributed to a massive increase in virulence, killing nearly 100% of unvaccinated chickens now vs causing mild disease decades ago.
CraigJPerry 5y ago
Does that not assume that you’re symptomatic at the same time you’re spreading the virus? With covid you appear to be able to spread before you know you have it. Given that, what force would cause the virus to be selected for less lethality? With a different presentation of disease where symptoms and spread occur concurrently then there would be a pressure on the virus selecting for strains that arent so lethal a carrier has no chance to spread. In covid’s case, that pressure doesn’t exist as far as i can see?
outworlder 5y ago
> I was under the impression viruses became less lethal because if they became more, they'd kill off their hosts and be less likely to spread. Only if the lethality is negatively impacting their fitness. If it can spread to another host quickly, who cares if the previous host dies. There's no selective pressure against it. Which is why Delta is scary. Not just because of the higher viral load, but new strains could be more lethal and still not be selected against.
deleted 5y ago
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AbortedLaunch 5y ago

It depends. It’s hard to model and even think about the selection pressures accurately. West Nile virus showed a marked increase in virulence in corvids recently as did rabbit hemorrhagic disease. And let’s not forget about Mareks disease, where a non-sterilizing vaccine is thought to have contributed to a massive increase in virulence, killing nearly 100% of unvaccinated chickens now vs causing mild disease decades ago.

CraigJPerry 5y ago

Does that not assume that you’re symptomatic at the same time you’re spreading the virus? With covid you appear to be able to spread before you know you have it. Given that, what force would cause the virus to be selected for less lethality? With a different presentation of disease where symptoms and spread occur concurrently then there would be a pressure on the virus selecting for strains that arent so lethal a carrier has no chance to spread. In covid’s case, that pressure doesn’t exist as far as i can see?

outworlder 5y ago

> I was under the impression viruses became less lethal because if they became more, they'd kill off their hosts and be less likely to spread. Only if the lethality is negatively impacting their fitness. If it can spread to another host quickly, who cares if the previous host dies. There's no selective pressure against it. Which is why Delta is scary. Not just because of the higher viral load, but new strains could be more lethal and still not be selected against.

deleted 5y ago

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