A new piece has just been added to the puzzle on the origins of Covid-19. An international team of scientists assured Thursday, March 16 to have for the first time found a link between animals sold on the seafood market in Wuhan (where the first official cases of Covid were recorded at the end of 2019) and the epidemic of Covid-19. In concrete terms, the analysis of Chinese genetic data – published and then deleted – from samples taken in early 2020 in and around the Wuhan market shows that the raccoon dogs, which were sold there illegally, could have “carried and perhaps excreted the virus at the end of 2019”, reports The Atlantic. This reinforces the hypothesis of a zoonotic origin of the pandemic which officially caused nearly 7 million deaths worldwide (at least double according to the WHO). Several of the researchers presented their findings on Tuesday (March 14) to the Scientific Advisory Group on the Origins of Novel Pathogens (SAGO), an expert group convened last year by the World Health Organization (WHO). A report containing all the details of this study is to be published in the coming days.
Let’s go back to the beginning. Shortly after the start of the pandemic, from January 1 to March 2, 2020, Chinese scientists went to the market in Wuhan, where several cases were detected, and took environmental swabs from walls, floors, metal cages and carts often used to transport animals. At that time, the place has been closed to the public and the animals have been evacuated for several days. More than three years later, the French researcher Florence Débarre flushes out “by chance” these genetic sequences first published in GISAID, a virological database, by Chinese researchers, before being deleted. Result: in the samples that came back positive for Sars-CoV-2, the scientists found genetic material belonging to animals, and largely to the raccoon dog.
What does this prove? “This is in addition to the large collection of results which go in the direction of a natural origin linked to the Wuhan market”, reacts to L’Express Florence Débarre. “This shows that animals were present at the market when the epidemic emerged,” she continues. This evidence is consistent with a scenario in which the virus spread to humans from an intermediate animal which could, therefore, be a raccoon dog. But let’s be specific: this does not definitively prove that any of these mammals were themselves infected, or even that they were the only animals in the market to have contracted the virus; nor does it prove that a raccoon dog served as an intermediate host between a bat and the human. But absence of proof is not proof of absence.
A raccoon dog photographed in Germany.
© / Biosphoto via AFP
Above all, these results are all the more surprising in that they contradict an initial publication by the group of Chinese scientists behind these samples, led by the director of the Chinese CDC George Gao, who had indicated that they had spotted in these samples of human genetic material, but not DNA from other animals sold on the market. The team, which had published its work on February 25, 2022 in the journal Research Square, suggested that humans had brought the virus to market. In other words, the market was not the origin of the pandemic, but simply a place of early spread. Why such a conclusion? And why did you delete the data afterwards? Contacted by Science, George Gao said the footage presented “nothing new”. “We knew there was an illegal trade in animals, and that’s why the market was immediately closed.” But the pressure will now be even stronger to push the Chinese authorities to make public all the footage at their disposal.
The hope of having access to raw data
If this new element does not solve the enigma of the origins of Covid-19, it reinforces the thesis of a natural overflow with the help of an intermediate animal potential. It remains to be determined whether raccoon dogs played the role of intermediate host and what was that of the Wuhan market: a place of emergence of the virus or an amplifier of the epidemic? Again, nothing has been done so far. “With this discovery, we would need to know if other animals were identified in the genetic sequences to know the quality of the sampling; and we would need to know where precisely the sequences are located in the phylogenetic tree of the epidemic and identify the presence of viruses in samples taken from animals at the market or on farms”, assures Etienne Decroly, of the CNRS. Basically, to understand if these samples are at the origin of the epidemic or simply the result of various contaminations.
In recent weeks, the lab leak theory, which posits that Sars-CoV-2 has a link (accidental or not) to the Wuhan Institute of Virology, has gained traction thanks to a new assessment. of the US Department of Energy. But market genetic data offers hard evidence of how the virus could have spread to humans from animals outside the lab. We already knew that viruses very close to Sars-CoV-2 (baptized BANAL) were discovered very far from Wuhan, in cavities in Laos, with a nucleotide identity of 97%. But it also suggests Chinese scientists have given an incomplete account of evidence that could provide details about the spread of the virus in the city market.
Because the new study is based on data that had been published, while the raw sequencing data was no longer available. “This study confirms, if necessary, that if we want to go further in the search for origins, we need transparency on the raw data. Without them, we cannot do science, but simply speculation” , regrets Etienne Decroly.