"We cannot say categorically how the pandemic started," Maria Van Kerkhove, an American epidemiologist at the World Health Organization (WHO), said in mid-March as the debate revived on the subject.

The scientific world widely believes that the pandemic started in early 2020 because a wild animal had, a few months earlier, transmitted the virus to humans, probably on the Chinese market of Huanan.

However, some researchers still defend the hypothesis of a laboratory leak, a priori the institute of Wuhan, the city of the market.

China strongly rejects this theory, but has also long denied that the Huanan market could have hosted animals that could transmit the virus.

What's up? Supporters of the laboratory hypothesis were encouraged at the end of February by the comments of US authorities, in particular the head of the FBI, on its "very likely" character.

The Huanan food market, March 30, 2020 in Wuhan, China, where Covid may have been transmitted from animals to humans © Hector RETAMAL / AFP/Archives

But, in contrast to their strong media impact, these statements have hardly changed the situation among scientists.

"These remarks do not seem to be based on new elements and (the laboratory leak, editor's note) remains the less convincing of the two hypotheses," said British scientist Alice Hughes, a biodiversity specialist, at the Science Media Center.

The raccoon dog

A few weeks later, proponents of natural transmission regained the media advantage, thanks to a study analyzing samples collected in early 2020 from the Huanan market.

Several American media, in particular the New York Times, relayed this work even before it was put online, presenting it as a major step forward to support natural transmission.

What is it? In early 2020, just after closing the Wuhan market, the Chinese authorities took numerous samples from the site. It is on these data that the researchers, led by the French Florence Débarre, worked.

Huanan market closes on March 30, 2020 in Wuhan, China © Hector RETAMAL / AFP/Archives

They spotted the DNA and RNA of several wild mammals, revealing their presence on the market shortly before it closed.

This is particularly the case of the raccoon dog. However, it is known that this animal, which belongs to the canine family but resembles a raccoon, can be infected with the coronavirus and, potentially, serve as an intermediary for contamination from bats to humans.

Does this work, which has not been published in a scientific journal, prove that the raccoon dog is at the origin of the pandemic? No, and it does not even allow us to say categorically that these animals were infected, since the samples were not taken directly from them.

Inaccessible data

However, this last hypothesis seems plausible since in some places on the market the DNA of these animals was very present next to that of the virus, while there was almost no human genome.

Only, even admitting their infection, it is impossible to say if they first contaminated a human or if things went the other way.

The raccoon dog, an animal that belongs to the canine family but resembles a raccoon, can be infected with the coronavirus and, potentially, serve as an intermediary for contamination from bats to humans © ALFREDO ESTRELLA / AE/AFP/Archives

This study is "a new piece of the puzzle that supports a link between the Wuhan animal market and the origin of the pandemic", but "not irrefutable proof", slices, on the site The Conversation, virologist Connor Bamford of Queen's University Belfast.

For him, it would be necessary to have older samples (at the end of 2019, when Covid emerged quietly) and directly carried out on animals.

However, this is a major problem in research on the origin of Covid: it is almost impossible to access raw data. This is even the case for those on which Ms. Débarre's team worked.

They were available on a platform accessible to researchers (Gisaid) but, since then, have been removed at the request of the Chinese researchers who had put them online.

"We have absolutely crucial data that shed light on the beginning of the pandemic (but) we cannot share them because they are not ours," Débarre told AFP.

However, "the more people who look into it, the more information we will be able to extract," she says.

© 2023 AFP