Our analysis indicates that the emergence of SARS-CoV-2 occurred through the live wildlife trade in China, and shows that the Huanan market was the epicenter of the COVID-19 pandemic.write the authors of the study, published in Science (New window)which has been peer-reviewed for several months.
Mapping to identify the epicenter
The researchers first tried to understand why, among the first data on COVID-19 cases, only 50 of the hundreds of people hospitalized at the start of the epidemic had a direct and traceable link with the Huanan market.
They mapped the cases, which revealed that many of these infected people lived near the market. Thus, the sellers and customers who were first infected at the market triggered a
chain of infections among community members in surrounding area. Unknowingly, these people then transmitted the virus to others in the community.
In fact, in this 7,770 square kilometer city, the majority of early cases were located in an area a few blocks from the market, not near the Institute of Virology – which is central to the theory. of the flight from the laboratory – located on the other side of the river.
By mapping the first infections, the researchers were also able to observe how, over time, they spread concentrically, from the Huanan market to the rest of the city.
Clues in samples and on social networks
Even before this study was published, many scientists agreed that live animal markets are ideal transmission hotbeds for the spread of new diseases. A study (New window) has also shown that nearly 50,000 animals – of 38 different species – were sold in Wuhan markets in the 18 months preceding the pandemic.
The study published on Tuesday also analyzed data from samples of liquids taken from drains and market stalls by China’s Centers for Disease Control and Prevention.
The majority of samples from the southwest side of the market were positive for SARS-CoV-2. It is in this area of the market where animals likely to be infected with coronaviruses were sold, including raccoon dogs, red foxes and badgers. And it is from this area that the first cases detected in December came from.
It is not a coincidence, wrote on Twitter Dr. Angela Rasmussen (New window)one of the study authors and a virologist at the Vaccine and Infectious Disease Organization (VIDO) at the University of Saskatchewan.
How do you know if the Huanan market was not just the place of a superspreader event?
Researchers looked at other markets and places with high population density in Wuhan to find out if they were the source of the pandemic.
They looked at social media data to compare traffic at hundreds of locations in Wuhan. Huanan Market had one of the lowest traffic rates, indicating that this location was less likely to be the site of a superspreader event.
On Twitter, Dr. Rasmussen clarified that it is difficult to determine which animal was the host of the virus, but that the samples also support the theory that a zoonosis – the natural transmission of disease or infection from a vertebrate animal to a human – is the cause of the pandemic.
Furthermore, another study (New window)also published on Tuesday in the journal Science, shows that market samples contained two variants of SARS-CoV-2. Thus, the researchers believe that the A and B lines appeared in the Huanan market in November or December 2019, and then spread to the surrounding districts.
2019″,”text”:”These results indicate that SARS-CoV-2 is unlikely to have circulated widely in humans before November 2019″}}”>These results indicate that SARS-CoV-2 is unlikely to have circulated widely in humans before November 2019., write the authors of the study. They add that
as with other coronaviruses, the emergence of SARS-CoV-2 likely resulted from multiple zoonotic events.
Further evidence that the virus did not come from a lab
In thread on Twitter (New window)Dr. Rasmussen explains that these elements again contradict the theory of a laboratory leak.
Although many questions remain unanswered, these results provide compelling evidence that SARS-CoV-2 emerged through at least two zoonoses from animals sold at Huanan Market.
One of the researchers, David Robertson, a virologist and professor at the University of Glasgow, told the BBC (New window) that he hoped their work would help
correct the false debate that the virus came from a laboratory.
Dr. Rasmussen also writes that there are still many questions to be answered and clarifies that their study cannot answer all questions about the origin of SARS-CoV-2. For example, which animals were first infected? Where did they come from? Were the animals also carriers of other coronaviruses?
These questions are essential to understand the risk of emergence of a SARS-CoV-3she writes, adding that we may never get answers to all the questions, but that the scientific community must continue its research work.
Dr. Rasmussen points out that any investigation into the origins of viruses can take years and that evidence is generally scarce and incomplete.years later, she points out, the origin of the Ebola virus is still not well understood.”,”text”:”For example, almost 50 years later, she points out, the origin of the Ebola virus is not yet well understood.”}}’>For example, almost 50 years later, she points out, the origin of the Ebola virus is still not well understood.