NEW YORK - An international team of virus experts said on Thursday that it had found genetic data from a market in Wuhan, China, linking the coronavirus with raccoon dogs for sale there.

The data added evidence to the case that the worst pandemic in a century could have been ignited by an infected animal that was being dealt through the illegal wildlife trade.

The genetic data was drawn from swabs taken in and around the Huanan Seafood Wholesale Market starting in January 2020, shortly after the Chinese authorities shut down the market because of suspicions that it was linked to the outbreak of a new virus.

By then, the animals had been cleared out, but researchers swabbed walls, floors, metal cages and carts.

In samples that came back positive for the coronavirus, the international research team found genetic material belonging to animals, including large amounts that they said were a match for the raccoon dog.

The jumbling together of genetic material from the virus and the animal does not prove that a raccoon dog itself was infected. And even if a raccoon dog had been infected, it would not be clear that the animal had spread the virus to people.

Another animal could have passed the virus to people, or someone infected with the virus could have spread it to a raccoon dog.

But the analysis did establish that raccoon dogs – fluffy animals that are related to foxes and known to be able to transmit the coronavirus – deposited genetic signatures in the same place where genetic material from the virus was left, three scientists involved in the analysis said.

That evidence, they said, was consistent with a scenario in which the virus had spilt into humans from a wild animal.

A report with the full details of the international research team’s findings has not yet been published. The analysis was first reported by The Atlantic.

The new evidence is sure to provide a jolt to the debate over the pandemic’s origins, even if it does not resolve the question of how it began.

In recent weeks, the so-called lab leak theory, which posits that the coronavirus emerged from a research lab in Wuhan, has gained traction thanks to a new intelligence assessment from the US Department of Energy and hearings led by the new Republican House leadership.

But the genetic data from the market offers some of the most tangible evidence yet of how the virus could have spilt into people from wild animals outside a lab.

It also suggests that Chinese scientists have given an incomplete account of evidence that could fill in details about how the virus was spreading at the Huanan market.

Dr Jeremy Kamil, a virus expert at Louisiana State University Health Sciences Centre Shreveport who was not involved in the study, said the findings showed that “the samples from the market that had early Covid-19 lineages in them were contaminated with DNA reads of wild animals”.

Dr Kamil said that fell short of conclusive evidence that an infected animal had set off the pandemic. But, he said, “it really puts the spotlight on the illegal animal trade in an intimate way”.

Chinese scientists had released a study looking at the same market samples in February 2022.

That study had reported that samples were positive for the coronavirus but suggested that the virus had come from infected people who were shopping or working in the market, rather than from animals being sold there.

At some point, those same researchers, including some affiliated with the Chinese Centre for Disease Control and Prevention, posted the raw data from swabs around the market to Gisaid, an international repository of genetic sequences of viruses.

Attempts to reach the Chinese scientists by phone on Thursday were unsuccessful.

On March 4, Dr Florence Debarre, an evolutionary biologist at the French National Centre for Scientific Research, happened to be searching that database for information related to the Huanan market when, she said in an interview, she noticed more sequences than usual popping up.

Confused at first about whether they contained new data, Dr Debarre put them aside, only to log in again last week and discover that they held a trove of raw data.

Virus experts had been awaiting that raw sequence data from the market since they learnt of its existence in the Chinese report from February 2022.

Dr Debarre said she had alerted other scientists, including the leaders of a team that had published a set of studies in 2022 pointing to the market as the origin.

An international team – which included Dr Michael Worobey, an evolutionary biologist at the University of Arizona; Dr Kristian Andersen, a virus expert at the Scripps Research Institute in California; and Dr Edward Holmes, a biologist at the University of Sydney – started mining the new genetic data last week.

One sample, in particular, caught their attention. It had been taken from a cart linked to a specific stall at the Huanan market that Dr Holmes had visited in 2014, scientists involved in the analysis said.

That stall, Dr Holmes found, contained caged raccoon dogs on top of a separate cage holding birds, exactly the sort of environment conducive to the transmission of new viruses.

The swab taken from a cart there in early 2020, the research team found, contained genetic material from the virus and a raccoon dog.

“We were able to figure out relatively quickly that at least in one of these samples, there was a lot of raccoon dog nucleic acid, along with virus nucleic acid,” said Dr Stephen Goldstein, a virus expert at the University of Utah who worked on the new analysis. Nucleic acids are the chemical building blocks that carry genetic information.

After the international team stumbled upon the new data, they reached out to the Chinese researchers who had uploaded the files with an offer to collaborate, hewing to rules of the online repository, scientists involved with the new analysis said. After that, the sequences disappeared from Gisaid.

It is not clear who removed them or why they were taken down.

Dr Debarre said the research team was seeking more data, including some from market samples that were never made public. “What is important is there is still more data,” she said. NYTIMES