SARS-CoV-2 jumped to humans without much change from bats

How much did SARS-CoV-2 have to change to adapt to its new human host? In a research article published in the open access journal PLOS Biology Oscar MacLean, Spyros Lytras at the University of Glasgow, and colleagues show that since December 2019 and for the first 11 months of the SARS-CoV-2 pandemic, very little ‘significant’ genetic change has been observed in the hundreds of thousands. consecutive virus genomes.

The study is a collaboration between researchers in the United Kingdom, the USA and Belgium. The lead authors Prof David L Robertson (at the MRC University of Glasgow Center for Virus Research, Scotland) and Prof Sergei Pond (at the Institute for Genomics and Evolutionary Medicine, Temple University, Philadelphia) were able to reverse their experience with data analysis of HIV and other viruses after SARS-CoV-2. Pond’s latest analytical framework, HyPhy, was instrumental in teasing the signatures of evolution embedded in the virus genome, and is based on decades of theoretical knowledge on molecular evolutionary processes.

The first author, dr. Oscar MacLean, explains: “It does not mean that no changes have taken place, that mutations of no evolutionary significance accumulate and ‘surf’ along the millions of transmission events, as in all viruses.” Some changes can have an effect; for example, the Spike replacement D614G which was found to improve transmissibility and certain other adaptations of virus biology spread across its genome. In general, however, ‘neutral’ evolutionary processes dominated. MacLean adds: ‘These stases can be attributed to the extremely sensitive nature of the human population to this new pathogen, with limited pressure on the population’s immunity and lack of childbirth, leading to exponential growth that makes almost every virus a winner. . ‘

Dammetjie’s comment: “What was so surprising was how transmissible SARS-CoV-2 was from the start. Usually, viruses that jump to a new host take some time to acquire adaptations to be as capable as to spread SARS-CoV-2, and most never get past that stage, leading to stagnant currents or localized outbreaks. ‘

The study of the mutation processes of SARS-CoV-2 and related sarbecoviruses (the group of viruses to which SARS-CoV-2 belongs from bats and pangolins), the authors find evidence of a fairly significant change, but all before the emergence of SARS-CoV- 2 in humans. This means that the ‘generalistic’ nature of many coronaviruses and their apparent ability to jump between hosts, soaked SARS-CoV-2 with a ready-made ability to infect humans and other mammals, but the traits probably developed in bats before it washes away for people.

Joint First Author and Ph.D. student Spyros Lytras adds: “Interestingly, one of the nearby bat viruses, RmYN02, has an interesting genomic structure consisting of both SARS-CoV-2-like and bat-like segments. The genetic material contains both different compositional signatures ( associated with the action of host antiviral immunity), which supported the change in evolutionary rate, occurred in bats without the need for an intermediate animal species. ‘

According to Robertson, the reason for the ‘shift of gears’ of SARS-CoV-2 is in terms of the increased rate of evolution at the end of 2020, which is associated with more heavily mutated sexes, because the immunological profile of the human population is changing . “By the end of 2020, the virus has increasingly come into contact with the existing immunity of the host, as the number of people previously infected is now high. It will opt for variants that may elude the host’s response. Along with the evasion of immunity in long-term infections in chronic cases (e.g. in patients with immunodeficiency), this new selective pressure increases the number of important virus mutants.

It is important to realize that SARS-CoV-2 is still an acute virus, which in the vast majority of infections is removed by the immune response. However, it is now moving faster away from the January 2020 variant used in all current vaccines to increase protective immunity. The current vaccines will continue to work against most circulating variants, but the more time passes, and the greater the difference between the number of vaccines and non-vaccines, the greater the chance of escape. Robertson adds: “The first race was to develop a vaccine. The race now is to get the world population vaccinated as quickly as possible.”