Briefly Noted for 2021-01-11
Briefly Noted for 2021-01-21(a)

Graydon: COVID Evolving: Comment—Noted

Graydon: COVID Evolving: Comment ‘SARS-CoV-2 derives from a bat disease. Bats are weird; bats, unlike nearly all other mammals, have two body temperatures. There's the high, active, flapping around body temperature and the low, resting/estivating, don't starve to death until you can feed again, hanging-upside-down-in-a-cave body temperature...

...Viruses are too simple to have multiple enzymes for different temperature ranges. (This is why lizard genomes are generally larger than mammal genomes; the mammal needs the enzymes for its stable body temperature. The lizard needs a range of enzymes for a range of temperatures. Viruses don't have the room; they've got one set of enzymes at most, often a partial set that relies on specific cellular machinery.) So bat viral diseases tend to have a "burst mode"; copy as much as possible before the temperature regime in this bat changes and we either freeze or burn.

We've known for a long time that the Rₜ for COVID-19 is highly variable; about a fifth of cases cause the majority of transmission in the wild type fo the disease. (Which is why the Japanese backtracking approach was effective; find the really infectious person and then find everybody they could have infected, rather than worrying about the tested-positive person, who (on the odds) wasn't going to spread the disease.) So maybe that's the burst-mode reproduction mechanism working in humans, some of the time. If that's the case, there's inevitable selection pressure for variants where the burst-mode reproduction works more reliably in humans; it's not so much random mutation as strong selection for any variant where this happens because reproduction is so much more successful for such variants.

Given that there are at least three, and probably more, such variants now known, I am finding this more plausible than I would like to find it…

.#commentoftheday  #2021-01-13