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.
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.
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.