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In order for there to be an evolutionary pressure toward becoming less severe, having higher severity has to give some disadvantage - e.g. killing the host befo
by m12k 5y ago
In order for there to be an evolutionary pressure toward becoming less severe, having higher severity has to give some disadvantage - e.g. killing the host before it can spread the disease or giving stronger symptoms so hosts can be isolated before they can spread it. The corona virus is pretty unique in how much it can spread before/without any symptoms showing up, which should mean there's relatively less room for improvement by lowering the severity.
- oezi 5y agoI think it is the other way around, there is no pressure to maintain a high severity as long as the virus can spread thus leading to mutations that lose the severe traits.
- lrem 5y agoUh, can you point at an example of a pressure to kill your host?
- oezi 5y agoNo that's why I said there is no pressure to be severe. Killing hosts doesn't provide many benefits (unless you spread via people touching dead bodies such as Ebola).
- red_trumpet 5y agoSurely such mutations can and will happen. But will they become dominant, if they do not provide any advantage?
- h0l0cube 5y agoPerhaps if it requires less energy to replicate and/or it invokes a weaker immune response?
- Quarrelsome 5y agosometimes the "best" team doesn't win the league. Its plausible.
- XorNot 5y agoViruses aren't trying to kill their hosts, they're trying to replicate. But to replicate they kill the cells they're in. COVID's severity is because it's making a tradeoff between the time it takes the immune system to destroy it, vs the need to get a host walking around and socializing while breathing it out onto new hosts. The lethality is a side-effect of its replication strategy.
- oezi 5y agoI thought the lethality was just the immune system running havoc. If a virus could achieve it, it would remain symptom-less and just spread.
- XorNot 5y agoViruses lyse (explode) the cells they take over in order to exit the cell, since packaging for membrane transport is much more complicated. Unchecked, they would just exponentially destroy your tissue. Cytokine storm responses are a particular kind of immune system over-reaction that can make relatively benign viruses much more dangerous to a healthy host then a more immunologically suppressed host, but that's not the behaviour of COVID-19 which is showing pretty standard lethality profiles.
- greendesk 5y agoCan someone explain whether corona is unique in this attribute of spreading versus other viruses? I would expect most cold-related viruses or other viruses in the human virome to exhibit this pattern.
- orra 5y agoAs you suspect, Coronavirus isn't unique in having an incubation period, or in being infectious during the latter part of the incubation period. Of course, there's questions of degree.
- chana_masala 5y agoAsymptomatic spread is a myth - https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2774102 https://jamanetwork.com/journals/jamanetworkopen/fullarticle...
- freemint 5y agoThe study you cite doesn't seem to say what you want it to say. > Controlling for differences across studies, secondary attack rates were higher in households from symptomatic index cases than asymptomatic index cases, to adult contacts than to child contacts, to spouses than to other family contacts, and in households with 1 contact than households with 3 or more contacts. It acknowledges asymptomatic spread.