Scientists have repeated their assertions of “compelling evidence” that Wuhan’s Huanan seafood and wildlife market was at the centre of the COVID-19 outbreak.
Two peer-reviewed studies published on 26 July re-examine information from the initial outbreak in the Chinese city. One shows that the earliest known cases were clustered around that market. The other uses genetic information to track the timing of the outbreak, reports BBC News.
It suggests there were two variants introduced into humans in November or early December 2019.
Together, the researchers say this evidence paints a picture that Sars-Cov-2 was present in live mammals that were sold at Huanan market in late 2019. They say it was transmitted into people who were working or shopping there in two separate “spillover events”, where a human contracted the virus from an animal.
One of the researchers involved, virologist Prof David Robertson from the University of Glasgow, told BBC News that he hoped the studies would “correct the false record that the virus came from a lab”.
Pandemic epicentre
Two years of scientific effort to understand the virus that causes COVID-19 have provided these researchers with a more informed perspective.
This has enabled them to address a key conundrum in the earliest patient data: That out of hundreds of people hospitalised with COVID-19 in Wuhan, only about 50 had a direct, traceable link to the market.
“It was really puzzling that most cases could not be linked to the market,” said Robertson. “But knowing what we know about the virus now, it’s exactly what we would expect, because many people only get very mildly ill, so they would be out in the community transmitting the virus to others and the severe cases would be hard to link to each other.”
This COVID-19 case-mapping research found that a large percentage of early patients, with no known connection to the market, meaning they neither worked nor shopped there, did turn out to live near it.
This supports the idea that the market was the epicentre of the epidemic, said Prof Michael Worobey, lead author and biologist from the University of Arizona, with sellers getting infected first and setting off a “chain of infections among community members in the surrounding area”.
“In a city covering more than 7,770sq km, the area with the highest probability of containing the home of someone who had one of the earliest COVID-19 cases in the world was an area of a few city blocks, with the Huanan market smack dab inside it,” said Worobey.
That study also zoomed in on the market itself. The scientists created a map of the samples – swabs of fluid from drains and on market stalls – that tested positive for the virus.
“Most of the positive samples clustered around the south-western side of the market,” said Robertson. “And that's the location where we report species like raccoon dogs being sold. So we have confirmation of animals we now know are susceptible (to Sars-Cov-2, the virus that causes COVID-19) were sold there in late 2019.”
The lab leak theory
Over the past two years, the search for the origin of the deadly pandemic turned from a scientific investigation into a toxic political row.
One of the subjects of a fierce international blame game, primarily between politicians in the US and China, was a theory that the virus could have been leaked from a Wuhan laboratory, the Wuhan Institute of Virology.
But that hypothesis, said Prof Stuart Neil from Kings College, “can’t explain the data”.
“We’re now as sure as we can be, based on the fragmentary evidence we have, that this was a spillover event that happened in the market.”
Crowded, live animal markets, many scientists agree, provide an ideal transmission hotspot for new diseases to “spill over” from animals. And in the 18 months up to the beginning of the pandemic, a separate study showed that nearly 50,000 animals, of 38 different species, were sold at markets in Wuhan.
Neil said the pandemic was very likely to have been a consequence of an “unhealthy, cruel and unhygienic practice that Chinese authorities had been warned about”.
The major risk of being distracted by looking for someone in a laboratory to blame for all this, he added, “is that we run the risk of letting this happen again because we’ve focused on the wrong problem”.
Study 1 details
The Huanan Seafood Wholesale Market in Wuhan was the early epicentre of the COVID-19 pandemic
Michael Worobey, Joshua I. Levy, Lorena Malpica Serrano, Alexander Crits-Christoph, Jonathan Pekar, Stephen GoldsteinH7, AngelaRasmussen Moritz G. Kraemer, Chris Newman, Marion Koopmans, Marc Suchard, Joel Wertheim, Philippe Lemey, David Robertson, Robert Garry , Edward C. Holmes, Andrew Rambaut, Kristian. Andersen
Published in Science on 26 July 2022
Abstract
Understanding how severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in 2019 is critical to preventing zoonotic outbreaks before they become the next pandemic. The Huanan Seafood Wholesale Market in Wuhan, China, was identified as a likely source of cases in early reports but later this conclusion became controversial. We show the earliest known COVID-19 cases from December 2019, including those without reported direct links, were geographically centred on this market. We report that live SARS-CoV-2 susceptible mammals were sold at the market in late 2019 and, within the market, SARS-CoV-2-positive environmental samples were spatially associated with vendors selling live mammals. While there is insufficient evidence to define upstream events, and exact circumstances remain obscure, our analyses indicate that the emergence of SARS-CoV-2 occurred via the live wildlife trade in China, and show that the Huanan market was the epicentre of the COVID-19 pandemic.
Study 2 details
The molecular epidemiology of multiple zoonotic origins of SARS-CoV-2
Jonathan Pekar, Andrew Magee, Edyth Parker, Niema Moshiri, Katherine Izhikevich, Jennifer Havens, Karthik Gangavarapu, Lorena Mariana Malpica Serrano, Alexander Crits-Christoph, Nathaniel Matteson, Mark Zeller, Joshua Levy, Jade Wang, Scott Hughes, Jungmin Lee, Heedo Park, Man-Seong Park, Katherine Zi Yan Ching, Raymond Tzer Pin Lin, Mohd Noor Mat Isa, Yusuf Muhammad Noor, Tetyana I. Vasylyeva, Robert F. Garry, Edward C. Holmes, Andrew Rambaut, Marc Suchard, Kristian G. Andersen, Michael Worobey, Joel Wertheim.
Published in Science on 26 July 2022.
Abstract
Understanding the circumstances that lead to pandemics is important for their prevention. Here, we analyse the genomic diversity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) early in the coronavirus disease 2019 (COVID-19) pandemic. We show that SARS-CoV-2 genomic diversity before February 2020 likely comprised only two distinct viral lineages, denoted A and B. Phylodynamic rooting methods, coupled with epidemic simulations, reveal that these lineages were the result of at least two separate cross-species transmission events into humans. The first zoonotic transmission likely involved lineage B viruses around 18 November 2019 (23 October–8 December), while the separate introduction of lineage A likely occurred within weeks of this event. These findings indicate that it is unlikely that SARS-CoV-2 circulated widely in humans prior to November 2019 and define the narrow window between when SARS-CoV-2 first jumped into humans and when the first cases of COVID-19 were reported. As with other coronaviruses, SARS-CoV-2 emergence likely resulted from multiple zoonotic events.
BBC News article – Covid origin studies say evidence points to Wuhan market (Open access)
See more from MedicalBrief archives:
‘Strong evidence’ of COVID-19’s origin in Wuhan live-animal market
Two new studies link coronavirus origins to China’s Huanan live-animal market
WHO report on COVID-19’s Wuhan origins ‘raises more questions than answers’