Scientists discredit raccoon dog Covid origin study

·4-min read
Raccoon dog
Raccoon dog

A study suggesting that raccoon dogs may have started the Covid pandemic is “risibly thin” and compiled by authors who have previously claimed to have “incontrovertible” proof of a market origin, scientists have warned.

On Monday evening a group of researchers published a pre-print saying they had found new evidence that animals capable of spreading Covid-19 were being sold at Huanan Seafood Market, where the earliest human cases were found.

One of the pre-print’s authors, Prof David Robertson of the University of Glasgow’s Centre for Virus Research, said the new data provided “strong evidence” that SARS-CoV-2 jumped to humans at the market.

Before publication, the story was leaked to The Atlantic, who claimed it was “the strongest evidence yet that an animal started the pandemic”.

Yet after the study was published last night, several experts said the claims were misleading, arguing that the sale of raccoon dogs at the market was already widely known, and that discovering their DNA proved little about the origins of the outbreak.

'No substantive new information'

A letter from Biosafety Now, a group of experts calling for tighter control on lab experiments which could create deadly pathogens, said: “The data provide no substantive new information about the origins of Covid-19, even if taken at face value.

“There is no evidence that this raccoon dog was even infected with SARS-CoV-2, as there was also human DNA in the sample, and the viral material could just as easily have come from an infected human.”

A statement from the Scientific Advisory Group for the Origins of Novel Pathogens, the World Health Organisation group looking into how the pandemic started, also stated that the paper “does not provide conclusive evidence as to the intermediate host or origins of the virus”.

The new sequences came to light after they were uploaded to an international genomic database by a Chinese group of researchers, including George Gao the former head of the Chinese Centre for Disease Control and Prevention.

Dr Gao, who is expected to publish his own findings on the DNA shortly, told the journal Science that the sequences did not resolve the question of the pandemic’s origin, which he said is “still scientific and open”.

His team published a pre-print last year showing that Covid-19 samples from the market contained human genetic material but no DNA from other animals, suggesting that humans brought the virus to the market.

But the new study, by a 19-strong international team, said they had found DNA from raccoon dogs, porcupines, bamboo rats, Himalayan marmots, masked palm civets and Siberian weasels and said the virus could have jumped from one of exotic species.

“Our findings reinforce the need for further analyses to address transmission between and from possible intermediate host species, and provide potential clues to the upstream events that led to the emergence of SARS-CoV-2 into humans,” said the pre-print, which has not been peer reviewed.

'Doesn't take us any further forward'

Viscount Ridley, who co-authored the book Viral: the Search For the Origins of Covid-19, said: “We’re in an odd situation where western virologists are frantically clutching at any straws to say the pandemic started in the market, while Chinese scientists closest to the sequences are saying it doesn’t come from the market. That’s pretty strange.

“All this paper proves is that raccoon dogs were in the market, and we already knew that. We just didn’t know they were there at the outbreak, and we still don’t because that DNA could have been left over from months earlier.

“I don’t think this takes us any further forward in our understanding of what happened.”

In a pre-print published in February, many of the same authors said they had “incontrovertible evidence” that Covid-19 emerged from the wildlife trade, but the claim was removed when the study was published in the journal Science.

Prof Richard Ebright, a molecular biologist from Rutgers University in the US, described the latest pre-print as “The Emperor’s New Clothes”.

“Turns out to be risibly thin, and nearly content free,” he said after the article was published.

Previous research has also shown that the biggest concentration of Covid was found near toilet blocks at the market rather than where animals were sold, suggesting the market was a super-spreader event rather than the origin of the pandemic.

The authors of the new pre-print also acknowledge that animal DNA in a sample does not mean that animal was the source of the virus.

“The most abundant animal in the sequencing data of a particular sample is not necessarily the source of the virus in that sample,” they write.