Three years after the appearance of Covid-19, debates on its origin are rebounding. Fueled by a recent study, the hypothesis of transmission by a wild animal largely dominates the scientific world, but the supporters of a laboratory leak are not giving up.
“We cannot say categorically how the pandemic started,” said Maria Van Kerkhove, American epidemiologist at the World Health Organization (WHO) in mid-March, when the debates were rekindling on this subject.
The scientific world widely believes that the pandemic started at the beginning of 2020 because a wild animal had, a few months earlier, transmitted the virus to humans, probably in 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 housed animals capable of transmitting the virus.
What's new ? Proponents of the laboratory hypothesis were encouraged at the end of February by the remarks of American authorities, in particular the boss of the FBI, on its "very probable" character.
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", judges the British scientist Alice Hughes, specialist in biodiversity, with the organization Science Media Center .
A few weeks later, supporters of natural transmission regained the media advantage, thanks to a study analyzing samples collected in early 2020 on 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 in supporting natural transmission.
What is it about ? In early 2020, just after closing the Wuhan market, the Chinese authorities took numerous samples from the site. It is on this data that the researchers worked, led by the Frenchwoman Florence Débarre.
They spotted the DNA and RNA of several wild mammals, which helps to prove their presence on the market shortly before it closed.
This is particularly the case of the raccoon dog. However, we know that this animal, which belongs to the canine family but looks like 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 the source of the pandemic? No, and it does not even allow us to state categorically that these animals were infected, since the samples were not taken directly from them.
However, this last hypothesis seems plausible since in certain places of the market the DNA of these animals was very present next to that of the virus, while there was hardly any human genome.
Only, even admitting their infection, it is impossible to say if they first infected a human or if things happened the other way around.
This study constitutes “a new piece of the puzzle which supports a link between the Wuhan animal market and the origin of the pandemic”, but “not irrefutable proof”, slice, on the site The Conversation, the virologist Connor Bamford of the Queen's University Belfast.
For him, it would be necessary to have older samples (at the end of 2019, when the Covid emerged quietly) and directly taken from 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 Mrs. Débarre's team worked.
They were available on a platform accessible to researchers (Gisaid) but have since been withdrawn at the request of the Chinese researchers who had put them online.
“We have absolutely crucial data which shed light on the start of the pandemic (but) we cannot share them because they are not ours”, regrets to AFP Ms. Débarre.
However, “the more people there are who look at it, the more information we will be able to extract”, she underlines.
03/24/2023 09:57:42 - Paris (AFP) - © 2023 AFP
