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Has Covid-19 passed from animals to humans on multiple occasions?

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Molecular biologists have discovered abnormalities in the phylogenetic tree of Sars-CoV-2 – a flowchart that shows how the virus has evolved since its discovery – which some scientists believe could indicate the coronavirus has passed from animals to humans to several times, according to a report from Nature.

The anomalies require further investigation, scientists told Nature, suspecting they are mainly the result of errors, but they raise a strong possibility that virtually diminishes the theory that the virus began to spread from it. ‘a laboratory.

covid origin

, which was the basis of the strongest theory to date that it originated in mammals before jumping to humans, either directly or via intermediate hosts.

Efforts to understand the evolution of Sars-CoV-2 are supported by genomic data submitted by thousands of laboratories around the world to what is known as the GISAID database. This database shows that all Sars-CoV-2 sequences go back to line A or line B, which were first sampled by laboratories in China.

Lineage B, according to the Nature article, is the dominant globally and was first seen in samples taken from people who visited the Huanan seafood market in Wuhan. The A lineage has spread in China, including to people who traveled to other markets in Wuhan, according to the report.

In a study cited in the Nature article, the dots between the two lineages do not meet – giving rise to the theory that patient zero in each of the lineages could have been different people, possibly infected with an animal.

The discrepancy was reported by molecular biologists who posted their results on virological.org, saying it was likely the result of errors in the submitted samples. But some scientists involved in the sampling say it is unlikely there were any errors, the Nature article continued.

“This is a very important study,” said the article quoting virologist Robert Garry. “If you can show that A and B are two separate lineages and there have been two fallouts, that virtually eliminates the idea that it (Sars-CoV-2) came from a lab,” the scientist said. , who works at Tulane University in New Orleans.

At the heart of the mystery are 38 genomes collected before February 28, 2020. These were considered transient, that is to say linking the two lineages. But, the researchers said they found other mutations that usually wouldn’t happen.

“The more we dug, the more it looked like, maybe we can’t trust any of the ‘transitional’ genomes,” the article said, citing study co-author Michael Worobey, a biologist at the evolution at the University of Arizona at Tucson. The authors suggest that a lab or computer error likely occurred while sequencing one of the two mutations in these “intermediate” genomes, which is not unusual.

That is why, said another researcher cited in the article, there must be more investigations. Xiaowei Jiang, an evolutionary biologist at Xi’an Jiaotong-Liverpool University in Suzhou, China, said the team behind the study must verify the results by obtaining “the raw sequencing data. original for as many genomes as possible ”.

It remains to be seen to what extent this will be possible. China has refused to grant more access to labs or data than it already has, prompting a World Health Organization (WHO) team to visit the country last year to conclude that the origins cannot be conclusively traced.


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