COVID-19: Live animals sold at the Wuhan Market are the source of the virus – Sade

Huanan Seafood Wholesale Market in Wuhan, China
Scientists say Sars-CoV-2 has likely jumped from animals to humans more than once (photo: Noel Celis/AFP)

An international team of scientists has just published, in the renowned journal Science, two articles with “robust evidence” that the Huanan Seafood Wholesale Market in Wuhan, China, was the epicenter of the COVID-19 pandemic. After a set of spatial, environmental and molecular analyses, the 18 researchers concluded that live animals sold at the establishment are the initial source of the coronavirus contagion to humans, and that this process occurred through multiple viral introductions.

For the team, the results practically eliminate suggested alternative scenarios for the emergence of the health crisis, such as the leakage of Sars-CoV-2 from a laboratory. “Analysis of the available evidence clearly suggests that the pandemic emerged from initial human infections of animals sold in the Huanan market at the end of November 2019”, emphasizes, in a statement, Kristian Andersen, a biologist in the Department of Immunology and Microbiology at the Scripps Research Institute. in La Jolla, United States, and author of both studies.
In one of the surveys, the team examined the places where the first cases of COVID-19 were recorded, as well as swab samples taken from surfaces at various locations in the Chinese market. Led by Michael Worobey of the University of Arizona and Andersen, the scientists determined the locations of nearly all 174 Covid-19 cases identified by the World Health Organization in December 2019 — 155 were in Wuhan. Analysis showed that these cases were clustered around the Huanan market, while later cases were widely dispersed across the Chinese city, which has more than 11 million people.
The study also shows that an “impressive percentage” of early COVID patients with no known connection to the market — neither working nor shopping there — lived close by. In Worobey’s assessment, this supports the idea that the market was the epicenter of the pandemic, “with vendors getting infected first and setting off a chain of infections among community members in the surrounding area.”

Another discovery made by the group reinforces this hypothesis. By analyzing the geographic distribution of later COVID cases, recorded in January and February 2020, they identified a “polar opposite” pattern of contagion, according to Worobey. Instead of being concentrated in the market, the infections were in areas of greater population density in Wuhan. “This tells us that the virus was not circulating cryptographically. It actually originated in that market and spread from there,” says the researcher.

Analyzes of swab samples taken from market surfaces such as floors and cages that tested positive for Sars-CoV-2 were “significantly associated” with stalls selling live wild animals. In addition, the group found that mammals now known to be susceptible to the virus, such as red foxes, badgers, and raccoon dogs, were sold live at the market in the weeks prior to the first recorded cases of COVID.

multiple species

According to Andersen, getting to the animal that was the host of the virus is a key issue and the answer is still unknown. “The raccoon has already been identified as a suspect, and it is possible, but we have nothing to prove it. In fact, it may not have been a single animal, but multiple species,” he said at a press conference. The hypothesis was raised by the group in light of the results of the second study, which focused on the analysis of genomic sequences from samples of viruses that infected people in the first weeks of the pandemic in China.

The research, led by Jonathan Pekar and Joel Wertheim, both at the University of California, San Diego, by Marc Suchard, at the University of California at Los Angeles, as well as Andersen and Worobey, indicates that Sars-CoV-2 has likely jumped. from animals to humans more than once. Analyzes show that the pandemic emerged from at least two separate human-animal infections at the Huanan market in November or December 2019, and initially involved two subtly distinct strains of the coronavirus.

Previous studies have reported on both strains, indicating that A, related to viral relatives in bats, would have given rise to B. The new study, however, shows that the two strains jumped from animals to humans on separate occasions. Wertheim explains that it is not so simple for a virus to migrate from one species to another and already evolve to the point of becoming transmissible between humans. “By comparing the virus genome, we saw that there was no way for lineage A (the original one) to evolve into lineage B, in humans. Instead, the simulations we did were much more consistent with distinct and separate introductions of the two lineages.” justifies.

Further analyzes carried out by the group brought more details about the onset of the infection. “We believe that most people who caught COVID early on did not transmit the virus. In fact, in 70% of cases, the virus could not survive. We propose that it probably took eight to 24 episodes of virus introduction to humans for the transmission of A and B lineages between people to be successful”, explains Wertheim.

The authors of the peer-reviewed studies suggest that to reduce the risk of new pandemics, scientists and public officials should seek a better understanding of the wildlife trade in China and elsewhere, as well as promote more comprehensive testing of live animals. sold in markets. “It is vital that we know as much as possible about the origin of COVID because only by understanding how pandemics start can we hope to prevent them,” emphasizes Wertheim.

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