Evidence that Wuhan market is source of COVID-19 outbreak

Analysis of genetic samples taken from the Huanan Seafood Market in Wuhan, China, has identified a list of wild animals sold there that are the most likely source of the virus that caused the COVID-19 pandemic.

Bats are thought to be the original vector for the SARS-CoV-2 virus, but it has previously been suggested that an intermediate wild species may have become infected and brought it to a market, where human infections began, where seafood as well as live animals were sold.

Another theory is that the virus leaked from the Wuhan Institute of Virology, where staff were known to have been studying bat coronaviruses, but not SARS-CoV-2.

However, a new study by an international team concludes that the virus likely originated from wild animals sold at the market, rather than being an escapee from a lab. The researchers reanalyzed data from 800 samples collected at the Huanan market by the China Center for Disease Control and Prevention from January 1, 2020, and also studied the viral genomes of the earliest COVID-19 cases.

Team member Ed Holmes, from the University of Sydney, said investigators in China swabbed surfaces, freezers, drains and cages to test for the presence of SARS-CoV-2.

“We analyzed these data to determine which species were present and where they were found in the market, specifically in relation to where SARS-CoV-2 was found,” Holmes said.

Contrary to statements by Chinese investigators, the team found evidence that a variety of wild animals sold at the market may have been intermediate hosts for the virus, including raccoon dogs.Nycterleutes procyonoides), Palm Civet (Pug bear larvae) and White Bamboo Mouse (Rhizomis pruinosus).

Importantly, Holmes said, these animal traces were found in the exact same stalls as SARS-CoV-2: “This suggests, but does not prove, that the animals were infected. It is therefore very likely that SARS-CoV-2 originated in a live animal market.”

“All the scientific data points in one direction, that the natural zoonotic origin of SARS-CoV-2 is the Huanan market in Wuhan,” Holmes said.

The researchers report that genetic studies of the virus in the earliest COVID-19 cases revealed that few, if any, people had been infected before the outbreak at the market, but they could not rule out the possibility that the virus was introduced to the market by an infected person who worked with animals.

Zach Hensel, a member of the research team at NOVA University in Lisbon, Portugal, said the study highlights the preventable risks posed by human-wildlife contact at the South China market and the need to mitigate such risks in similar locations.

“Of course, there were people everywhere in the Huanan market, and live mammals were concentrated in a few stalls, but human viruses other than SARS2 were rare, and several animal viruses were quite abundant,” Hensel says.

“This included influenza viruses with zoonotic potential, as well as animal viruses that are closely related to other viruses that have caused devastating epizootics.”

Hansel said simple personal protective equipment, which was recommended in these settings before COVID-19, may have prevented the entire pandemic.

Robert Edwards of Flinders University in Adelaide, Australia, who was not involved in the study, said the latest research was carried out by a “dream team of evolutionary biologists.”

“The origin of SARS-CoV-2 in a wet market is now beyond doubt,” Edwards said. “While the authors argue that humans initiated the infection at the market, alternative origin theories must explain why the market was the only source of so many infections.”