“A virus doesn't get more virulent naturally”
Listen up everyone- Sierra’s just reinvented virology- isn’t it exciting
totally incorrect - but, exciting
“One is
in a region called the polybasic cleavage site, which is known to make other coronaviruses and flu viruses more infectious. Another appears to make the spike protein less fragile, and in lab experiments with cell cultures, it
makes the virus more infectious. The mutation has become more common as the Covid-19 pandemic goes on, which suggests — but does not prove — that it makes the virus more infectious in the real world, too. (Fortunately, though it may increase spread, it doesn’t seem to make people sicker.)
This evolutionary two-step — first spillover, then adaptation to the new host — is probably characteristic of most viruses as they shift hosts, says Daniel Streicker, a viral ecologist at the University of Glasgow. If so, emerging viruses probably pass through a “silent period” immediately after a host shift, in which the virus barely scrapes by, teetering on the brink of extinction until it acquires the mutations needed for an epidemic to bloom.
Streicker sees this in studies of rabies in bats — which is a good model for studying the evolution of emerging viruses, he says, since the rabies virus has jumped between different bat species many times. He and his colleagues looked at decades’ worth of genetic sequence data for rabies viruses that had undergone such host shifts. Since larger populations contain more genetic variants than smaller populations do, measuring genetic diversity in their samples enabled the scientists to estimate how widespread the virus was at any given time.
The team found that almost none of the 13 viral strains they studied took off immediately after switching to a new bat species. Instead, the viruses
eked out a marginal existence for years to decades before they acquired the mutations — of as yet unknown function — that allowed them to burst out to epidemic levels. Not surprisingly, the viruses that emerged the fastest were those that needed the fewest genetic changes to blossom”
https://www.smithsonianmag.com/science-nature/how-viruses-evolve-180975343/
