They confirm that the Covid-19 originated in the live animal market in Wuhan

• Coronavirus New studies refocus the origin of Covid on the Wuhan market

• Pandemic A fishmonger in the Wuhan market is the first known case of Covid

A team of researchers from the University of Arizona (United States) has confirmed that

Huanan Seafood Wholesale Market in

, Hubei Province (China), were the

Covid-19 pandemic.

.

Led by the university's virus evolution expert Michael Worobey, international teams of researchers have traced the start of the pandemic to the Wuhan market.

Their findings have been published this Tuesday in two articles in the journal

.

The publications, which have since undergone peer review and include additional analysis and conclusions, virtually eliminate alternative scenarios that have been suggested as the origin of the pandemic.

Furthermore, the authors conclude that

from animals likely

in the Huanan market in late November 2019.

One of the studies scrutinized the locations of the earliest known cases of Covid-19, as well as swab samples taken from surfaces at various market locations.

The other focused on the genomic sequences of SARS-CoV-2 from samples collected from Covid-19 patients during the first weeks of the pandemic in China.

The first work, led by Worobey and Kristian Andersen at the Scripps Research Institute in San Diego, California, examined

, December 2019. The team was able to determine the location of nearly all of the 174 Covid-19 cases identified by the World Health Organization that month, 155 of which were in Wuhan.

Analyzes showed that these cases clustered tightly around the Huanan market, while subsequent cases were widely dispersed across Wuhan, a city of 11 million people.

In particular, the researchers found that

no known connection to the market (meaning they didn't work or shop there)

.

"This supports the idea that the market was the epicenter of the epidemic," says Worobey, explaining that vendors became infected first and caused a chain of infections among community members in the surrounding area.

"In a city that covers more than 5,000 square kilometers, the area most likely to contain the home of someone who had one of the first cases of Covid-19 in the world was an area of ​​a few streets, with the Huanan market right inside it," says Worobey, who directs the Department of Ecology and Evolutionary Biology at the University of Arizona.

But this conclusion was supported by another finding.

When the authors looked at the geographic distribution of subsequent Covid cases, from January and February 2020, they found a "diametrically opposite" pattern, in Worobey's words.

While

.

"This tells us that the virus was not circulating cryptically," says the researcher.

"It really originated in that market and spread from there," he says.

Cases of people hospitalized

"It is important to realize that all these cases were people who were identified because they were hospitalized," says the expert.

"None were mild cases that could have been identified by knocking on the doors of people living near the market and asking if they were feeling unwell," he adds.

In other words,

," he stressed.

To rule out any possibility of bias, Worobey's team went one step further.

Starting with the market, they began removing cases from their analysis, moving further and further away from the market, and ran the statistics again.

The result was that

.

"Even in that scenario, with most of the cases cleared, we found that the remaining ones lived closer to the market than would be expected if there were no geographic correlation between these early Covid cases and the market," Worobey said.

Positive tests associated with stalls selling live wild animals

The study also

, after the market closed.

Samples that tested positive for SARS-CoV-2 were significantly associated with stalls selling live wild animals.

The researchers determined that mammals now known to be susceptible to SARS-CoV-2, including

, were being sold live at the Huanan market in the weeks before the first recorded cases of the virus.

Covid-19.

"Upstream events remain obscure, but our analyzes of available evidence strongly suggest that

at the Huanan Seafood Wholesale Market in late November 2019," Andersen said. , co-lead author of both studies.

The virus could have jumped from animals to humans more than once

The second study, an analysis of SARS-CoV-2 genomic data from early cases, was co-led by Jonathan Pekar and Joel Wertheim of the University of California, San Diego, and Marc Suchard of the University of California, Los Angeles. Angeles, both in the United States, as well as by Andersen and Worobey.

They determined that the pandemic, which initially involved two subtly distinct lineages of SARS-CoV-2, likely arose from at least two separate human infections of animals in the Huanan market in November 2019 and perhaps December 2019. The analyzes also suggest that, in this period,

.

The authors used a technique known as

, which relies on the natural rate at which genetic mutations occur over time, to establish a framework for the evolution of SARS-CoV-virus lineages. two.

They found that the hypothesis of a single introduction of the virus into humans, rather than multiple introductions, would be inconsistent with molecular clock data.

Previous studies had suggested that one lineage of the virus -- named A and closely related to viral relatives in bats -- gave rise to a second lineage, named B.

Most likely, based on the new data, is a scenario where

, both in the Huanan market, according to Worobey.

Thus, the two studies provide evidence that Covid-19 originated by jumping from animals to humans in the Huanan market, probably after transmission to those animals from

.

Going forward, the researchers say that scientists and government officials should seek to better understand the wildlife trade in China and elsewhere and promote more extensive testing of live animals sold in markets to reduce the risk of future pandemics.

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