Newly published studies conclude that animals sold at Wuhan market likely started Covid-19 pandemic

Two newly published studies conclude that the Huanan Seafood Market in Wuhan, China, was most likely the epicenter for the coronavirus.

The studies were posted online as preprints in February but have now undergone peer review and were published Tuesday in the journal Science.

In one, scientists from around the world used mapping tools and social media reports to do a spatial and environmental analysis.

They suggest that although the “exact circumstances remain obscure,” the virus was probably present in live animals sold at the market in late 2019.

The animals were held close together and could easily have exchanged germs. However, the study does not determine which animals may have been sick.

The researchers determined that the earliest Covid-19 cases were centered at the market among vendors who sold these live animals or people who shopped there.

Researchers believe that there were two separate viruses circulating in the animals that spilled over into people.

“All eight COVID-19 cases detected prior to 20 December were from the western side of the market, where mammal species were also sold,” the study says.

The proximity to five stalls that sold live or recently butchered animals was predictive of human cases.

The “extraordinary” pattern that emerged from mapping these cases was very clear, said another co-author, Michael Worobey, department head of Ecology and Evolutionary Biology at the University of Arizona.

The researchers mapped the earliest cases that had no connection 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 spreading in people who worked at the market but then started that spread … into the surrounding local community as vendors went into local shops, infected people who worked in those shops,” Worobey said.

The other study takes a molecular approach and seems to determine when the first coronavirus infections crossed from animals to humans.

The earliest version of the coronavirus, this research shows, probably came in different forms that the scientists call A and B. The lineages were the result of at least two cross-species transmission events into humans.

The researchers suggest that the first animal-to-human transmission probably happened around November 18, 2019, and it came from lineage B. They found the lineage B type only in people who had a direct connection to the Huanan market.

The authors believe that lineage A was introduced into humans from an animal within weeks or even days of the infection from lineage B. Lineage A was found in samples from humans who lived or stayed close to the market.

“These findings indicate that it is unlikely that SARS-CoV-2 circulated widely in humans prior to November 2019 and define the narrow window between when SARS-CoV-2 first jumped into humans and when the first cases of COVID-19 were reported,” the study says. “As with other coronaviruses, SARS-CoV-2 emergence likely resulted from multiple zoonotic events.”

The likelihood that such a virus would emerge from two different events is low, acknowledged co-author Joel Wertheim, an associate adjunct professor of medicine at the University of California, San Diego.

To reduce the chances of future pandemics, the researchers hope they can determine exactly what animal may have first become infected and how.