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Raccoon dogs blamed for the Covid pandemic were not responsible, a new analysis suggests, after samples at a Wuhan market were found to contain virtually no virus.
Last month a controversial study suggested that raccoon dog DNA found at Huanan Seafood Wholesale Market in January 2020 was mixed with Covid-19, providing ‘strong evidence’ that the coronavirus jumped to humans from animals .
The paper was based on swabs taken by Chinese market researchers at the start of the pandemic and recently uploaded to an international database. The authors said it pointed to a zoonotic origin for the pandemic rather than a laboratory leak.
But a new in-depth genetic analysis of samples by respected computational virologist Dr Jesse Bloom, of the Fred Hutchinson Cancer Center in Seattle in the United States, has shown that there is almost no Covid-19 mixed with the raccoon dog’s DNA.
Of the 14 raccoon dog samples studied, 13 did not have Covid-19 at all, while one had only one fragment of the virus for every 200 million fragments of animal DNA.
Conversely, the virus has been found in larger quantities mixed with human DNA, as well as species such as largemouth bass, catfish, cowfish, carp and snakefish, none of which could transmit the virus to humans.
The team concluded that there actually was a “negative correlation” between Covid-19 and raccoon dog DNA.
Dr Bloom also cautioned that the samples were taken several weeks after the first cases of Covid emerged in Wuhan, at a time when Covid-19 had already been widely spread in the market by humans.
“What can we conclude about the origins of Covid-19 from all of this? Probably not much,” he told her.
“We should analyze everything, but this data doesn’t tell us how the pandemic started.
“Environmental samples taken more than a month after humans began shedding the virus do not reliably indicate the origin of the outbreak.
“If we ever know the origin of Sars2, I suspect it will come from information about events that happened in November 2019 or earlier.”
The Huanan Seafood Wholesale Market has been associated with a cluster of first cases, which has led some scientists to suggest that that’s where COVID-19 jumped from animals to humans.
Raccoon dogs were considered a likely candidate because they were known to be susceptible to the virus, but no DNA linking the animal to Covid-19 had ever been found.
Earlier this year, a group of Chinese scientists uploaded genetic data from swabs taken on the market during the early days of the pandemic that appeared to show raccoon dog DNA mixed with Covid-19.
The upload was spotted by Dr Florence Débarre, an evolutionary biologist at France’s National Center for Scientific Research, who published an unpeer-reviewed report with colleagues saying it showed “strong evidence” of an animal spillover.
Ahead of publication, the story was also leaked to The Atlantic, which said it was “the clearest evidence that an animal started the pandemic”.
The Chinese scientists who collected the original samples published their study in the journal Nature saying there was no way to know if raccoon dogs were infected and cautioning that the origin of Covid could not be determined from their samples.
The researchers pointed out that humans had already been infected when they first took swabs in January 2020, so even if the animals had been infected, they could have gotten the virus from humans.
The Chinese team also found Covid-19 in sewers, suggesting that infected humans or animals may have helped spread the virus. Previous studies have highlighted that the largest concentration of Covid-19 was found near the toilets in the market.
The Huanan Seafood Wholesale Market was located a few kilometers from the Wuhan Institute of Virology which was collecting and conducting experiments on bat coronaviruses, the closest relatives of Covid-19.
Last week a US Senate committee released a 300-page report concluding that the pandemic most likely stemmed from a lab leak that resulted from a “research-related” incident in Wuhan.
The report said the theory that Covid-19 jumped from animals to humans in a market “no longer deserves the benefit of the doubt or a presumption of accuracy”.
