Scientists found the strongest evidence yet that the coronavirus SARS-CoV-2 jumped from animals to humans in a market in China, leading the first reported outbreak of COVID-19. The genetic data was uploaded to a public database and then immediately deleted at the request of the Chinese team who shared it first.
An international team of scientists reported that swabs taken in and around the stalls at the Huanan Seafood Wholesale Market in early 2020 contained genetic sequences of SARS-CoV-2 mixed with the DNA of common raccoon dogs (Nyctereutes procyonoides). The Atlantic Ocean (opens in new tab) first reported the findings on Friday (March 17). Raccoon dogs, a fox relative with dark spots around their eyes, are known to be able to carry and transmit the coronavirus. That reports the New York Times (opens in new tab).
Given when and how the swabs were collected, and the fact that the virus cannot persist indefinitely in the environment without a host, the analysis suggests that raccoon dogs infected with SARS-CoV-2 may have a contagious virus excreted while illegally traded on the market in December 2019, the team concluded.
The analysis, which is not yet complete and has not yet been published, cannot prove with certainty that infected raccoon dogs were present on the market. And if the animals were infected, the research cannot show how they contracted the virus or how the virus spread from there.
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However, the presence of SARS-CoV-2 and genetic material from raccoon dogs in the exact same swabs at least suggests that infected wild animals were on the market and thus had the potential to spread the virus, the scientists said.
“This is a very strong indication that animals on the market were infected,” Angela Rasmussen (opens in new tab), a virologist involved in the study told The Atlantic. “There’s really no other explanation that makes sense.”
The newly analyzed genetic sequences were uploaded to GISAID, an open-access genomic database, earlier this month by researchers affiliated with China’s Center for Disease Control and Prevention (CDC), according to The Atlantic. Evolutionary biologist Florence Debarre (opens in new tab) saw that the raw sequence data had been shared and alerted other researchers.
Just hours after downloading the data from GISAID, scientists followed through Christian Andersen (opens in new tab), Edward Holmes (opens in new tab)And Michael Worobey (opens in new tab) discovered raccoon dog DNA mixed with SARS-CoV-2 genetic material. The team presented their findings Tuesday (March 14) to the World Health Organization’s (WHO) Scientific Advisory Group on the Origin of Novel Pathogens, The Atlantic reported.
In February 2020, China’s CDC researchers had analyzed the same data, but published only part of it, without mentioning raccoon dog DNA. They reported in a preprint finding an “abundance” of it homo sapiens DNA (opens in new tab) associated with SARS-CoV-2, which they said infected people were marketing the virus to. They couldn’t find any evidence pointing to an animal host in that data, they wrote. But graphs in the same preprint contradicted that claim animal DNA was found mixed with SARS-CoV-2 (opens in new tab)Science first reported in 2022.
Shortly after Tuesday’s WHO meeting, the Chinese research group’s preprint for 2020 was reviewed in a peer-reviewed Nature Research journal, suggesting a new version will be published soon.
The team that presented their findings to WHO initially contacted the Chinese researchers to collaborate on the study, but shortly after they reached out, the genetic sequences were removed from GISAID, The New York Times reported.
GISAID noted that the sequences were removed at the request of the submitter, Science reported (opens in new tab). When asked why the sequences were not shared sooner, former head of China’s CDC George Gao told Science that the data “[n]something new. It was known that there was illegal trade in animals, so the market was closed immediately.” question of the origin of SARS-CoV-2which he said is “still scientific and open”.
Critics of the widely held spillover hypothesis – that SARS-CoV-2 jumped from animals to humans – may ultimately want more conclusive evidence than research can provide, Joel Wertheim (opens in new tab)an evolutionary biologist involved in the analysis told Science.
“You can’t observe the zoonotic transmission of a new virus from animals to humans,” he said. “We’re just never going to get to that level of data.”