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by azangru
1996 days ago
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> Is there any theory or data that more the R or transmission rate less deadly the virus is in itself? There's a vague evolutionary argument that the less deadly for the host a parasite is the more widely it can spread and thus the more evolutionarily successful it will become. But there is no mechanism that guarantees the inverse — that an increase in infectiousness will be accompanied by a decrease in lethality. From the molecular biological perspective, the molecules responsible for viral spread and the molecules responsible for the damage that the virus does to its host (or that the host does to itself when attacking the virus) are likely to be quite different, so there is no reason for a change in one to be accompanied by a change in the other. |
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I’m not clear; the argument effectively defines infectiousness as how-not-lethal the virus is. Thus, the virus cannot be made more infectious without decreasing lethality.
There is however an interim period, as evolutionary arguments are long-term arguments, where the virus can be both more infectious and more deadly, before settling into its stationary state.
The molecular perspective isn’t too useful against an evolutionary argument as well — evolution is always a sum-of-the-parts system. The question is simply: is the virus ultimately more capable of spreading? And at least in the extreme, an instantly killed host is unlikely to do an real spreading, no matter how trivially the virus could spread (had the host persisted). And in the other extreme, a completely non-lethal virus can survive and spread forever, especially in dense populations, especially if it doesn’t incapacitate the host significantly (acting as a simple parasite), allowing it to continue meeting new hosts.
Of course, a virus that doesn’t need the victim to be the host is a different story; eg malaria persists and spreads through mosquitos, so it could instantly kill humans and yet receive no evolutionary pressure against it.