BEIJING — International experts agree that the presence of raccoon dog DNA in samples of COVID-19 found in a Chinese market close to where the first human cases were identified provides further support for the idea that the virus originated in animals rather than in a laboratory.
World Health Organization Director-General Tedros Adhanom Ghebreyesus said on Friday that the data do not provide a definitive answer to how the pandemic began, but that every piece of data is important in moving us closer to that answer.
It is still unknown what caused the emergence of the coronavirus. Like many other viruses before it, many scientists think it likely spread from animals to humans at a wildlife market in Wuhan, China. Scientists say it’s possible the virus spread from one of the many labs in Wuhan dedicated to collecting and studying coronaviruses.
The new findings have not been reviewed by other experts or published in a peer-reviewed journal, so they cannot be considered definitive.
At a press briefing, Tedros said, “this data could have and should have been shared three years ago.” He was critical of China for waiting so long to reveal the genetic information.
The first human cases of COVID-19 were discovered in late 2019, and the samples were taken from surfaces at the Huanan seafood market in Wuhan in early 2020.
According to Tedros, researchers at China’s Center for Disease Control and Prevention have just uploaded the genetic sequences to the largest public virus database in the world.
They were subsequently taken down, but not before a biologist in France happened upon them by accident and passed the data along to researchers investigating the coronavirus outside of China.
Evidence suggests that animals involved in the wildlife trade may have been infected with COVID because some of the samples tested positive for the virus also contained raccoon dog genes, as reported by the researchers. The Atlantic was the first publication to report on their findings.
“There’s a good chance that the animals that deposited that DNA also deposited the virus,” said Stephen Goldstein, a virologist from the University of Utah who helped analyze the data. “If you went out and did environmental sampling after a zoonotic spillover event, this is basically exactly what you would expect to find,” the authors write.
Due to their raccoon-like appearance, these dogs are commonly bred for their fur and then slaughtered for food in animal markets all over China.
Epidemiologist Ray Yip, who helped establish the Chinese branch of the US Centers for Disease Control and Prevention, deemed the results to be noteworthy but not conclusive.
By far the strongest evidence to support animal origins is the market environmental sampling data published by China CDC,” Yip told the AP in an email. He had nothing to do with the latest findings.
Maria Van Kerkhove, the technical lead for COVID-19 at the WHO, cautioned that the investigation did not find the virus in any animals and did not provide definitive evidence that any animals infected humans.
This does give us some hints as to what may have happened, she said. She also mentioned that the international team reported to WHO that they discovered raccoon dog DNA in addition to DNA from other animals in the seafood market samples.
Scientists believe COVID-19 came into human populations either directly from a bat or indirectly through an animal such as a pangolin, ferret, or racoon dog due to the genetic code’s striking similarity to that of bat coronaviruses.
The massive increase in human infections during the first two years of the COVID-19 pandemic, as well as an increasingly bitter political dispute, have complicated efforts to trace the pandemic’s origins.
A related virus, SARS, baffled virus experts for over a decade before they finally traced it back to animals.
According to Goldstein and coworkers, their analysis provides the first convincing evidence that infected wildlife may have been sold at the market. However, it’s also possible that the raccoon dogs contracted the virus from humans who brought it to the market or who accidentally left infected bodily fluids nearby.
The group’s scientists reportedly contacted the China CDC, and the sequences were subsequently removed from the global virus database. The delay in disclosing information from samples taken more than three years ago has baffled researchers. Tedros has pleaded with China to release more information about the COVID-19 virus.
Despite an email request from the Associated Press, Gao Fu, the former head of the Chinese CDC and lead author of the Chinese paper, has yet to respond. However, he argued that the sequences are “nothing new” in an interview with Science magazine. The market was closed immediately because of reports of illegal animal trading
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Goldstein reported this week that the WHO advisory panel looking into the origins of COVID-19 had been presented with the findings of his group.
Finding a sample with sequences from the virus and a raccoon dog “places the virus and the dog in very close proximity,” as microbiology and immunology expert Michael Imperiale of the University of Michigan put it, who was not involved in the data analysis. But this doesn’t prove the dog was infected, only that they shared a small space.
He noted that studies published last summer suggested the market was the likely early epicenter of the scourge and concluded that the virus spilled over from animals into people twice. He concluded that the weight of scientific evidence at this point supports a natural exposure at the market. The professor questioned the likelihood of two separate lab leaks.
University of Edinburgh infectious disease expert Mark Woolhouse has said it will be crucial to compare the genetic sequences of raccoon dogs to what is known about the historical evolution of the COVID-19 virus. “That’s probably as good evidence we can expect to get that this was a spillover event in the market,” he said, if the dogs are confirmed to have COVID and the viruses from which they contracted it are shown to have an earlier origin than the ones that infected people.
WHO spent weeks in China investigating the source of the pandemic, and in 2021 they released a report saying that COVID-19 probably spread to humans from animals and that its origin in a laboratory was “extremely unlikely.”
The next year, however, the UN health agency reversed course, claiming that “key pieces of data” were still missing. In addition, Tedros has stated that all possibilities should be considered.
In February, researchers from the China Centers for Disease Control and Prevention who had previously analyzed the Huanan market samples published a preprint paper indicating that they believed humans, rather than animals, were responsible for bringing the virus to the market. Animal genes were found in the positive samples, but this fact was left out of their paper.
It was reported in February by the Wall Street Journal that the US Department of Energy had “low confidence” that the virus had escaped from a laboratory. However, some members of the US intelligence community disagree and think it was actually developed by animals first.
It may be years, if ever, before the true cause of the pandemic is discovered, according to experts.
