A study on the origin of the Covid-19 virus, published this Thursday, September 19, revealed new elements reinforcing the hypothesis that the infection was transmitted to humans by contaminated animals present in a market in Wuhan (China) at the end of 2019.
Nearly five years after its appearance, the international scientific community has still not managed to identify with certainty the source of the virus responsible for the Covid-19 pandemic.
The first cases of Covid were detected in late 2019 in Wuhan, giving rise to two conflicting theories: a leak from a laboratory in the city where related viruses were being studied, or the infection of an intermediary animal that transmitted the virus to people frequenting the local market. The scientific community favors the second hypothesis.
The study, published in the journal Cell, is based on the analysis of more than 800 samples collected from the market, where various types of wild animals are sold.
These samples were taken in January 2020, after the market closed, from different surfaces and stalls, including those selling wild animals, as well as from the sewer network.
With this data provided by Chinese scientists, ” We cannot definitively say whether the animals (present on the market) were infected or not.“, says Florence Débar, researcher at the National Center for Scientific Research and co-author of the study.
She told AFP that ” Our study confirms the presence of wild animals in this market at the end of 2019, including species such as raccoon dogs and civets. These animals were in the southwest part of the market, which is also the area where many SARS-CoV-2 viruses responsible for Covid-19 have been identified.”.
The presence of these species on the market has been denied, but they have been identified as potential intermediate hosts of the virus between bats and humans. To date, only photographic evidence and study results describing the animals sold in Wuhan have been revealed.
As part of the study, contaminations of ” animal transport carts, a cage, a garbage bin and a plucking and plucking machine from a wildlife stand” with the SARS-CoV-2 virus were found. These samples contained “more DNA from wild mammals than from humans« .
Wildlife ribonucleic acid was found in positive samples from this site, including species such as civets, bamboo rats and raccoon dogs.
The authors of the study point out that ” These data indicate either that the animals present in this stand excreted the SARS-CoV-2 virus, traces of which were found on the machinery used for the animals, or that early, unreported human infections of Covid-19 transmitted the virus in the same place where the animals were discovered.Another element suggests that the market was a starting point for the spread of the virus.
The study showed that the ” last common ancestor (MRCA) » of SARS-CoV-2 present in market samples, i.e. the original strain, is « genetically identical ” to the most recent common ancestor of the entire pandemic. Débar explained: ” This means that the early diversity of the virus was present in the market, and we expect to see if this is where the virus emerged.”.
For his part, James Wood, an epidemiologist at the University of Cambridge, said that this new study ” provides compelling evidence that wildlife stalls in the market (…) were the hotbed of the emergence of the Covid-19 pandemic”.
He stressed that ” This study is important” because, despite efforts “globally to improve biosafety in laboratories, no significant steps have been taken to reduce wildlife trade, biodiversity loss or land-use changes, which are potential drivers of past and future pandemics”.
