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Coronavirus

Researchers trace COVID-19 origin to sales of live animals at Wuhan seafood market

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A team of international researchers have traced the origin of COVID-19 to the sale of live animals at the Huanan Seafood Wholesale Market in Wuhan, China.

The origin of the pandemic – which has killed 6.4 million globally – has been a mystery since the COVID-19 virus first emerged at the end of 2019.

Read the latest updates in our dedicated coronavirus section.

The studies, led by the University of Arizona, traced the start of the pandemic to the sale of live foxes, raccoon dogs and other mammals which were susceptible to the virus before the pandemic’s onset.

The research was published in the journal Science on Tuesday.

In the first study, scientists from Scripps Research and the University of Arizona analyzed the geographic pattern of the cases that emerged during the first month of the COVID-19 outbreak in December 2019. They were able to determine the locations of nearly all 174 infections – identified by the World Health Organization at the time – concluding that 155 of those 174 cases were in Wuhan.

These early cases were clustered tightly around the Huanan market, with later cases spreading throughout wider Wuhan, a city with a population of almost 11 million, their analysis showed. In addition, a large percentage of early COVID-19 patients had no history of visiting the market but resided very close to it, compared to others, supporting their theory that the market was the epicenter of the pandemic, the study’s lead author, Michael Worobey, said.

The building of Huanan seafood market, where the second floor remains open for optics stores, and where coronavirus believed to have first surfaced, almost a year after the start of the coronavirus disease (COVID-19) outbreak, in Wuhan, Hubei province, China December 8, 2020. Picture taken December 8, 2020. (Reuters)
The building of Huanan seafood market, where the second floor remains open for optics stores, and where coronavirus believed to have first surfaced, almost a year after the start of the coronavirus disease (COVID-19) outbreak, in Wuhan, Hubei province, China December 8, 2020. Picture taken December 8, 2020. (Reuters)

He added that vendors were the first to get infected, subsequently setting off a chain of COVID-19 infections among community members in the areas surrounding the market.

“In a city covering more than 3,000 square miles, 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,” Worobey said in a statement on Tuesday.

He also said that there was another finding to support this conclusion. When the researchers looked at the geographical distribution of the COVID-19 cases that followed, recorded in January and February 2020, they found a “polar opposite” pattern, coinciding with areas of the highest population density in Wuhan.

“This tells us the virus was not circulating cryptically,” Worobey said. “It really originated at that market and spread out from there.”

In an important addition to their earlier findings, the researchers addressed the question of whether health authorities found cases around the market simply because that is where they looked.

“It is important to realize that all these cases were people who were identified because they were hospitalized. None were mild cases that might have been identified by knocking on doors of people who lived near the market and asking if they felt ill. In other words, these patients were recorded because they were in the hospital, not because of where they lived,” Worobey said.

The researchers also analyzed swab samples from the market’s floors, cages, and other surfaces that had been closed and they found that positive samples tended to come from stalls that sold live wildlife.

They concluded that animals now known to be susceptible to COVID-19, including red foxes, hog badgers, and raccoon dogs, were sold in the Huanan market in the weeks prior to the first recorded COVID-19 cases. The team ended up developing a detailed map of the market, showing that positive samples reported by Chinese scientists in early 2020 were clearly associated with the western portion of the market, which was the area where merchants butchered meat and sold live animals in later 2019.

“Upstream events are still obscure, but our analyses of available evidence clearly suggest that the pandemic arose from initial human infections from animals for sale at the Huanan Seafood Wholesale Market in late November 2019,” explained Kristian Andersen, co-senior author of both studies and a professor in the Department of Immunology and Microbiology at Scripps Research.

In the second study, the scientists combined epidemic modeling with analyses of COVID-19’s early evolution based on the earliest possible sampled genomes. They determined that the pandemic rose from at least two separate human infections due to animal contact at the market in November and December 2019.

Their findings also suggested that there were several animal-to-human virus transmissions at the market, but that these failed to develop into COVID-19 infections.

The research team concluded that COVID-19 originated from animal-to-human transmission at the Huanan market and that the animals most probably contracted the virus from COVID-carrying bats in the wild or on local farms inside China, putting alternative origin theories to rest.

“To more fully understand the origin of SARS-CoV-2, we need to more fully understand events upstream of the Huanan market, which will require close international collaboration and cooperation,” Andersen said.

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