SARS-CoV-2 jumped from bat to human without major changes

How much did SARS-CoV-2 need to be modified to adapt to the new human host?Research papers published in open access journals PLOS Biology Oscar McLean, Spyros Lytras of the University of Glasgow, and colleagues have seen few hundreds of thousands of “significant” genetic changes during the first 11 months of the SARS-CoV-2 pandemic since December 2019. It shows that. Sequenced viral genome.

This study is a collaborative study by researchers in the United Kingdom, the United States and Belgium. Lead authors Professor David L Robertson (MRC-Center for Virus Research, University of Glasgow, Scotland) and Professor Sergei Pond (Institute of Genomic Evolutionary Medicine, Temple University, Philadelphia) have been able to change the experience of data analysis. From HIV and other viruses to SARS-CoV-2. HyPhy, Pond’s state-of-the-art analytical framework, helps elicit signs of evolution embedded in the viral genome and is based on decades of theoretical knowledge of molecular evolutionary processes.

Lead author Dr. Oscar McLean said, “This does not mean that no changes have occurred, but that evolutionarily insignificant mutations have accumulated and, like all viruses, millions of transmission events. “Surfing” along. ” Some changes may affect you. For example, spike substitution D614G, which has been shown to enhance transmissibility, and other specific tweaks of viral biology scattered throughout its genome. But overall, the “neutral” evolutionary process dominated. McLean said, “This stagnation may be due to the highly sensitive nature of the human population to this new pathogen, due to limited immunity pressure from the population and lack of containment. It leads to exponential growth and almost every virus wins. “

Ike commented, “What is very surprising is how infectious SARS-CoV-2 was from the beginning. Usually, the virus that jumps to a new host species is the same as SARS-CoV-2 when it spreads. It takes time to acquire adaptation to be as capable as it is, and in most cases it does not go through that stage, resulting in dead-end spillover effects and local outbreaks. “

When studying the mutation process of SARS-CoV-2 and the associated salvecovirus (a group of viruses in which SARS-CoV-2 belongs to the bats and pangolins), the authors found evidence of a fairly significant change. , All before the advent of SARS-CoV-. 2 for humans. This means that the “generalist” nature of many coronaviruses and their apparent ability to jump between hosts has imbued SARS-CoV-2 with its ready-made ability to infect humans and other mammals. However, these traits probably evolved in bats before the spillover effect on humans.

Spyros Lytras, co-lead author and PhD student, adds: “Interestingly, one of the closer bat viruses, RmYN02, has an interesting genomic structure composed of both SARS-CoV-2-like and bat virus-like segments (host antiviral immunity). Both different compositional features (related to action) support this change in the pace of evolution that took place in bats without the need for intermediate animal species. “

Robertson said, “The reason for the” gear shift “of SARS-CoV-2 in terms of increased evolutionary rate at the end of 2020, which is associated with more highly mutated strains, has changed the immunological profile of the population. “With the current high number of previously infected people, the virus is in increasing contact with existing host immunity towards the end of 2020, which can dodge part of the host’s response. Variants that can be selected. These new selective pressures, coupled with immune avoidance in long-term infections in chronic cases (eg, immunocompromised patients), are increasing the number of significant viral variants.

It is important to understand that SARS-CoV-2 is still an acute virus and is eliminated by the immune response of the majority of infectious diseases. However, it is currently rapidly transitioning from the January 2020 variant used in all current vaccines to boost protective immunity. Current vaccines continue to work for most of the circulating mutants, but the longer the elapsed time and the greater the difference between the number of vaccinated and unvaccinated people, the greater the vaccine. You will have more chances to escape. “The first competition was to develop a vaccine. The competition now is to get people around the world to get the vaccine as soon as possible,” Robertson added.