Do three new studies add up evidence of COVID-19’s origins in an animal market in Wuhan? | Science
Do three new studies add up evidence of COVID-19’s origins in an animal market in Wuhan?  |  Science

Do three new studies add up evidence of COVID-19’s origins in an animal market in Wuhan? | Science

Three new studies provide one indisputable conclusion about the origins of SARS-CoV-2: Despite the course of 2 years and the Chinese government’s lack of transparency, data still exists that may shed light on the pandemic’s biggest mystery. And while these new analyzes do not all reach the same conclusion as to how COVID-19 was triggered, each undermines the theory that the virus somehow escaped from the Wuhan Institute of Virology, which has long been a focus of suspicion.

The studies examine various aspects of the viral spread at Huanan Seafood Market in Wuhan, China, the city where the first cases were discovered. Two international efforts are based on the fact that SARS-CoV-2 jumped to humans from infected animals – a zoonotic leap – on the market, probably twice, at the end of 2019. A third, pretty much Chinese efforts describe early signs of coronavirus in environmental and animal samples from the market, but suggests that the virus was imported there, perhaps from outside countries – a conclusion that Michael Worobey of the University of Arizona, an evolutionary biologist who is a similar author to the two international studies, calls “a huge disruption.”

The studies were published as pre-printed and have not been peer reviewed, but scientists, biosafety experts, journalists and others are already intensely investigating their details. “I have been brought closer to the zoonosis side with these pre-prints,” says Flo Débarre, an evolutionary biologist at the French National Research Bureau (CNRS), who has followed the origins debate closely and has not cast his lot with either natural origins or the lab leak camp. Evolutionary biologist William Hanage of Harvard University agrees that these studies “will be taken as a blow” to the hypothesis of laboratory leakage. “They are significantly moving the needle of origin in the direction of the market,” Hanage says.

Skeptics of the theory of natural origin claim that the market cluster could only be a superspreader event that was affected when someone infected with a laboratory-escaped coronavirus visited it. But Worobey believes additional data could make that claim even less tenable. In particular, a more transparent analysis of the market’s genetic sampling data can identify exactly which animal species are sold there that carry the virus.

In a study, Worobey and colleagues describe two subtly different lineages of SARS-CoV-2 was found in humans at Huanan Seafood Market in late 2019, which they take as a sign that the virus jumped twice from animals to humans there. Their second studio offers one geospatial analysis of the earliest human cases identifying the market as the “epicenter” of the emergence of SARS-CoV-2, showing both genera of infected people who had connections to the market or lived near it. It also links the specific stalls in the market where live animals were sold to environmental samples that are known to have tested positive for the virus. “Together, these analyzes provide dispositive evidence for the emergence of SARS-CoV-2 through wildlife trade and identify the Huanan market as the unambiguous epicenter of the COVID-19 pandemic,” they conclude.

Worobey and colleagues had hoped to release their preprints next week, but hastened their plans and opted for a preprint server that delivers without delay when the Chinese study was published on February 25 on the Research Square website. Led by George Gao of the Chinese Academy of Sciences and co-author of 37 other scientists (one is from Canada), this research – based on data previously leaked to the media but never officially published – provides the most detailed description to date of environmental samples that it Chinese Center for Disease Control and Prevention obtained at Huanan Seafood Market between January 1 and March 2, 2020.

In the new pre-print, Gao and colleagues analyzed 1,380 samples from 188 animals on the market and in the environment, including sewer wells, soil, removal machines and “containers.” They found SARS-CoV-2 in 73 samples. But because everyone was from the environment, not the animals themselves, they claim that humans introduced the virus to the market. The authors call the market an “amplifier”, not the source of SARS-CoV-2.

Closely related to the government’s claims about the origin of COVID-19, the oppression of Gao and colleagues notes studies that have reported evidence of SARS-CoV-2 in other countries before it appeared in Wuhan, without mentioning criticism attributing this evidence to pollution. . It also hovers a highly controversial theory that frozen foods imported into China may have been the original source. (The newspaper’s writers, including Gao, did not respond to requests to discuss the work.)

The Corona lineage analysis from Worobey and colleagues refines an argument put forward by virologist Robert Garry last year. In data on the early human cases, Garry had identified two different forms of SARS-CoV-2 that differ only in two mutations that he claimed appeared in different Wuhan markets in December 2019. The new work, which includes Garry as a co-author and citing evidence from the GAO study, significantly transforms this scenario. It concludes that both genera, christened A and B, originated in the Huanan Seafood Market and quickly spread to nearby neighborhoods. B probably jumped from animals to humans in late November 2019, leading to the first detected case on December 10, and pedigree A a few weeks later, the group concludes. Either way, the team claims that the almost simultaneous emergence of two lineages challenges the dissertation on laboratory origin, as it would require two different viruses to leak at roughly the same time. (GAO and colleagues also found both SARS-CoV-2 lines in their environmental samples.)

The second advance from the international team is based on a Chinese-led study from June 2021, which spent 2 years documenting a tick fever in mammals for sale in a specific stall on the market. The new study points for the first time where species susceptible to SARS-CoV-2 – including raccoon dogs, hedgehogs, badgers, red foxes and bamboo rats – were sold and map these sites for the positive environmental samples, including in one “container” think the authors were a cage. “To anyone who really understands what’s in all these three papers, I think it’s very hard to deny that this is a very, very, very strong case that this pandemic started in that market, “says Worobey.

Others say they are not final. “These are interesting studies, but I do not think they close the case of what happened to the origin of the virus,” said Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Center, who has criticized colleagues for overly dismissing laboratory hypotheses. . “I am particularly skeptical of the conclusion that there must have been two zoonotic leaps.”

He notes that in about 10% of human transmissions of SARS-CoV-2, the virus acquires two mutations, meaning that a different lineage could have arisen after the infection of the first human instead of two zoonotic leaps. Worobey, Garry, and colleagues did a computer simulation that challenges Bloom’s claim. They modeled what would have happened if there was an introduction of a single lineage and compared it with viruses sequenced from Wuhan cases until January 23, 2020. By matching the sequence data from the actual epidemic, they found that there was only a 3.6% chance that a single genus mutated into another.

The environmental samples from the Wuhan market, which tested positive for SARS-CoV-2, may be able to resolve the stalemate over the origin of the virus if they can detect a specific animal source of the virus. “If you find a positive sample with lots of raccoon dog DNA, for example, you have a hit,” says evolutionary biologist David Robertson of the University of Glasgow, co-author of the epicenter.

But the prejudice of Gao and colleagues only notes that these samples contain DNA from many animals without specifying which – other than humans. “The authors have already done the analysis, they just have not put all the necessary results to interpret them in their paper,” says evolutionary biologist Andrew Rambaut from the University of Edinburgh, a co-author of both studies. “This will no doubt be rectified if the paper gets through peer review.”

Yet Worobey and his co-authors even admit that evidence may not be enough to end this polarizing debate. “With the way people have been able to just push any evidence aside that points away from a laboratory leak, I fear that even if there was evidence from one of these samples that was full of red fox DNA and SARS-CoV -2 that people might say, ‘We still think it actually came from the driver of the red fox,’ Worobey says.

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