(Paris) A study on the origins of COVID-19 published Thursday provides new elements reinforcing the hypothesis of transmission to humans by infected animals introduced to a market in Wuhan (China) at the end of 2019.
Nearly five years after its emergence, the international scientific community has still not managed to determine with certainty the origin of COVID-19.
Although the first cases were initially detected in Wuhan at the end of 2019, two theories are currently being considered: a leak from a laboratory in the city where similar viruses were being studied, or an intermediary animal that infected people who frequented a local market. The scientific community favours this last theory.
The study published Thursday in the journal Cell is based on the analysis of more than 800 samples collected in this market where different species of wild animals were sold.
Collected in January 2020, after the market closed, they were taken from surfaces, from various market stalls, including those selling wild animals, and from sewers.
With this type of data, made available to researchers by Chinese scientists, “we cannot say with certainty whether the animals [présents sur le marché] were infected or not,” warns Florence Débarre, researcher at the CNRS and co-author of the study.
But, “our study confirms that there were wild animals in this market at the end of 2019, including species such as raccoon dogs and civets. And that these animals were present in the southwest corner of the market, which also happens to be an area in which many SARS-CoV-2 viruses, responsible for COVID-19, have been detected,” she explained to AFP.
The presence at the market of these species, identified as probable intermediate hosts of the virus between bats and humans, has been disputed and until now only photographic evidence and the results of a study describing the animals sold in Wuhan were available.
Infected cages
As part of the study, “animal carts, a cage, a garbage cart and a hair and feather removal machine from a wildlife stand” tested positive for SARS-CoV-2 and there was “more DNA from wild mammal species than human” in these samples.
Wildlife DNA was found in positive samples from this stand, including species such as civet cats, bamboo rats and raccoon dogs.
“These data indicate that either animals present at this stall shed SARS-CoV-2 detected on animal equipment or that unreported early human cases of COVID-19 shed the virus at the exact same location as the detected animals,” the study authors explain.
Another element points to the market as the starting point for the spread of the virus.
The study establishes that the “most recent common ancestor (MRCA)” of SARS-CoV-2 found in the market samples, i.e. the original strain, is “genetically identical” to the MRCA of the pandemic as a whole.
“This means that the early diversity of the virus is found in the market, as you would expect to see if this is the place of emergence,” says M.me Get out.
This new study “provides very strong evidence that wildlife stalls in the market […] were a hotbed of the COVID-19 pandemic,” James Wood, an epidemiologist at the University of Cambridge, told the Science Media Center.
“This work is important,” he said, because despite efforts “on a global scale to strengthen laboratory biosafety […]little or nothing has been done to limit the live wildlife trade, biodiversity loss or land use changes, which are the likely real drivers of past and future pandemic outbreaks.”