A new genetic analysis of the virus that caused Covid-19 taken from more than 7,600 patients worldwide shows that this virus has been circulating in humans since the end of last year, and must have spread very quickly after the first infection.
Researchers in the UK looked at mutations in the virus and found evidence of rapid spread, but there was no evidence that the virus became more easily transmitted or was more likely to cause serious illness.
“This virus is changing, but this by itself does not mean getting worse,” geneticist Francois Balloux of the University College London Genetics Institute told CNN.
Balloux and colleagues drew a string of viruses from a giant global database used by scientists around the world to share data. They looked at samples taken at different times and from different places, and said they showed that the virus first infected people at the end of last year.
“This leaves aside any scenarios that assume SARSCoV-2 might have circulated long before being identified, and therefore have infected a large portion of the population,” wrote Balloux’s team in their report, published in the journal Infection, Genetics and Evolution.
That is bad news. Some doctors expect the virus to circulate for months and may have secretly infected more people than was reported. That would offer hope that there might be immunity already established in some populations.
“Everyone hopes for that. Me too,” Balloux said.
Their findings poured cold water on such an idea. At best, 10% of the global population has been exposed to the virus, Balloux estimates.
Between humans and bats
Many different studies show that the new coronavirus, which is often called SARS-CoV-2 by scientists, originates from bats but must have infected other animals before jumping into humans. The first human case was reported in Wuhan, China, last December.
Viruses make mistakes every time they replicate themselves, and this mutation can be used as a so-called molecular clock to track viruses through time and geography.
“Our results are in accordance with previous estimates and show all sequences sharing a common ancestor towards the end of 2019, supporting this as a period when SARS-CoV-2 jumps to human hosts,” the team wrote.
“This is very new,” Balloux said. “We are absolutely sure that the host leap took place late last year.”
That’s because virus samples taken from all over the world show many mutations, and they are similar mutations. “Everything is everywhere,” the team wrote.
“This has been introduced and introduced and introduced in almost all countries,” Balloux added.
They also found genetic evidence supporting the suspicion that the virus had infected people in Europe, the US and elsewhere weeks or even months before the first official cases were reported in January and February. It is impossible to find a “first” patient in any country, Balloux said.
“All these ideas about trying to find Zero Patients are useless because there are so many zero patients,” he said.
The Balloux team’s findings were reviewed by other experts, a process called peer review, before being published in the journal. He said several reports by other teams, which were published online on a website called pre-printed, might have drawn the wrong conclusions.
“All viruses mutate naturally. Mutations in themselves are not a bad thing and there is no suggestion that SARS-CoV-2 mutates faster or slower than expected. So far we cannot say whether SARS-CoV-2 is more or less less deadly and contagious, “Balloux said.
Lane Warmbrod is an analyst at the Johns Hopkins Center for Health Security who has tracked reports about the genetics of the new corona virus. He said more research was needed on animals to show how genetic changes in the virus could make it more or less infectious or pathogenic.
“Just because this research tells us that this mutation quickly spreads or becomes dominant doesn’t mean anything unless we know it happened. It doesn’t really tell us anything about what is happening biologically,” Warmbrod told CNN.
Reports about mutations can be important for teams working on drugs and vaccines to fight the corona virus. Vaccines, in particular, need to target portions of the virus that are conserved – which do not change much over time.
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