For the last three years, the origin of the COVID-19 pandemic has been a topic of debate. Now, new data of environmental samples collected at a seafood and meat market in Wuhan, China suggests that raccoon dogs being illegally sold at the market may have been the source of SARS-CoV-2.
In February 2022, Chinese scientists released a study looking at the samples collected from the Wuhan market and argued that the samples that were positive for the coronavirus came from infected people rather than animals sold in the market.
However, in January, the researchers released the sample data on an open-access genomic data base called GISAID. It was then that Florence Débarre, an evolutionary biologist at the French National Centre for Scientific Research, discovered the data and alerted her colleagues.
"A scientist on the team noticed the data come online by happenstance, and because they often check the GISAID database," said Alexander Crits-Christopher, a senior scientist in computational biology at Cultivarium. "She shared the data with an international team and realized the relevance and importance of the data. This team then immediately contacted the data generators in the hopes of open communication and collaboration. The team then immediately alerted the [World Health Organization] about the presence of the data, and the WHO has helped mediate that communication. All three of the parties above have iterated a shared goal of making data and analyses as open as possible, as soon as possible."
According to the researchers, the samples contain evidence that raccoon dogs illegally sold at the market had left DNA behind in the same place where the genetic signatures of the new coronavirus had been discovered. However, the data does not definitively prove a raccoon dog was infected with the coronavirus.
Raccoon dogs are native to East Asia and can act as intermediary hosts — meaning they can pick up diseases from other sources and transmit them to humans — having spread tapeworms, rabies, coronaviruses, and other pathogens in the past. Raccoon dogs are commonly sold in wet markets that sell other live animals all stacked on top of each other.
"When these animals are in those situations where they get stressed, they are more likely to shed virus," said Krysten Schuler, a wildlife disease ecologist at Cornell University's College of Veterinary Medicine. "They're a bridge species that could cause the virus to adapt and be more likely to transmit to humans."
The team of scientists has not yet released a paper on the findings but did present an analysis to a WHO advisory group studying the origins of COVID-19.
Shortly after the research team offered to collaborate on the analysis with the Chinese researchers, the gene sequences were removed from GISAID, the New York Times reports, leading WHO to issue a statement urging China to release the data.
"These data could have — and should have — been shared three years ago," said Tedros Adhanom Ghebreyesus, WHO's director general. The missing evidence now "needs to be shared with the international community immediately," he added.
"The big issue right now is that this data exists and that it is not readily available to the international community," said Maria Van Kerkhove, an epidemiologist at WHO, adding that "[a]ny data that exists on the study of the origins of this pandemic need to be made available immediately."
Van Kerkhove noted that more studies need to be carried out on the samples. "These studies have been recommended over many years, looking at the source of the animals of the market, looking at potential intermediate hosts, looking at breaches in biosafety biosecurity," she said. "These studies have yet to be conducted, and until they are conducted, until we have the data, we aren't able to conclusively say how this pandemic began."
Some experts said that while the study may not definitively prove a raccoon dog was the source of the coronavirus, it seems likely.
"We don't have proof of the so-called smoking raccoon dog," said Angela Rasmussen, a virologist at the University of Saskatchewan. "We just have evidence that the animals were in the same part of the market where we know there was a virus."
However, Rasmussen added, the evidence does make it "more likely that an animal contributed the viral sequences that were in there."
"It's exactly what you'd expect if the virus was emerging from an intermediate or multiple intermediate hosts in the market," said Sarah Cobey, an epidemiologist and evolutionary biologist at the University of Chicago. "I think ecologically, this is close to a closed case."
Arturo Casadevall, an immunologist at the Johns Hopkins Bloomberg School of Public Health, said the data adds to the evidence of a natural spillover event.
"I would say it strengthens the zoonotic idea, that is, the idea that it came from an animal at the market," he said.
Without an actual animal that first spread the virus to people, determining the origins of the COVID-19 pandemic will always involve weighing probabilities, Casadevall added. In this case, any animals being sold at the market were removed before researchers started taking samples in early 2020, making it impossible to find the exact source.
Some experts cautioned the study doesn't prove a raccoon dog was the source of the coronavirus.
David Relman, a professor of microbiology and immunology at Stanford University, said the new data is "very inconclusive."
"Frankly, the breathlessness and alacrity with which stories like this one are promoted, in the face of very incomplete and confusing 'data,' leaves me frustrated and concerned," he said.
"Scientifically, it doesn't prove that raccoon dogs were the source, but it sure smells like infected raccoon dogs were at the market," said Jeremy Kamil, a virologist at Louisiana State University Health Sciences Center Shreveport, adding that it "raises more questions about what the Chinese government really knows."
"Do we know the intermediate host was raccoon dogs? No," Kristian Andersen, one of the co-authors of the analysis, said. "Is it high up on my list of potential hosts? Yes, but it's definitely not the only one." (Mueller, New York Times, 3/17; Doucleff/Beaubien, "Goats and Soda," NPR, 3/17; Wu, The Atlantic, 3/18; Achenbach/Johnson, Washington Post, 3/17; Rosenzweig-Ziff, Washington Post, 3/17)
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