The researchers determined that the first cases of Covid-19 were concentrated in the market among the vendors who sold these live animals or the people who shopped there. They believe there were two separate viruses circulating in the animals that spilled into humans. “All eight cases of COVID-19 detected before December 20 were from the west side of the market, where mammal species were also sold,” the study said. Proximity to five stalls selling live or freshly slaughtered animals was predictive of human cases. “The clustering is very, very specific,” study co-author Christian Andersen, a professor in the Department of Immunology and Microbiology at Scripps Research, said Tuesday. The “remarkable” pattern that emerged from mapping these cases was very clear, said another co-author, Michael Worobey, head of the Department of Ecology and Evolutionary Biology at the University of Arizona. The researchers mapped the first cases unrelated to the market, Worobey noted, and those people lived or worked in close proximity to the market. “This is an indication that the virus started to spread to people working in the market, but then it started to spread to the surrounding local community as vendors went into local stores, infected people who worked in those stores,” Worobey said. The other study takes a molecular approach and appears to determine when the first coronavirus infections passed from animals to humans. The earliest version of the coronavirus, this research shows, likely came in different forms that scientists call A and B. The lineages were the result of at least two cross-species transmission events in humans. The researchers suggest that the first animal-to-human transmission likely occurred around November 18, 2019, and originated from the B lineage. They found the B lineage type only in people who had a direct connection to the Huanan market. The authors believe lineage A was introduced to humans from an animal within weeks or even days of being infected by lineage B. Lineage A was found in samples from humans who lived or stayed near the market. “These findings indicate that it is unlikely that SARS-CoV-2 circulated widely in humans before November 2019 and define the narrow window between the first circulation of SARS-CoV-2 in humans and the reporting of the first cases of COVID- 19. ” says the study. “As with other coronaviruses, the emergence of SARS-CoV-2 likely resulted from multiple zoonotic events.” The likelihood of such a virus arising from two separate events is low, admitted co-author Joel Wertheim, an associate professor of medicine at the University of California, San Diego. “Now, I realize it sounds like I just said that a once-in-a-generation event happened twice in short succession, and pandemics are indeed rare, but when all the conditions are present — this is a zoonotic virus capable of both human infection as well as human transmission in close proximity to humans — the barriers to diffusion have been reduced so that we believe multiple introductions should be expected,” Wertheim said. Andersen said the studies don’t definitively disprove the lab leak theory, but they are extremely convincing, so much so that he has changed his mind about the origin of the virus. “I was pretty convinced about the lab leak until we looked at it very carefully and looked at it much more closely,” Andersen said. “Based on data and analysis that I’ve done over the last decade on many other viruses, I’ve convinced myself that the data actually points to this particular market.” Worobey said he too believed the lab leak was possible, but the epidemiological preponderance of market-linked cases “is not a mirage.” “It’s a real thing,” he said. “It is simply not plausible that this virus was introduced in any way other than the wildlife trade.” To reduce the chances of future pandemics, researchers hope they can determine exactly which animal may have first been infected and how. “The raw ingredients for a zoonotic virus with pandemic potential are still lurking in the wild,” Wertheim said. He believes the world needs to do a much better job of policing and monitoring animals and other potential threats to human health. Andersen said that while we can’t prevent outbreaks, collaboration among the world’s scientists could be the key to the difference between a low-impact disease and one that kills millions. “The big question we have to ask ourselves is — the next time this happens, why does it happen — how can we detect this outbreak early and prevent this outbreak from becoming a pandemic?”
