Coronavirus seems to come from the Wuhan covered market after all

An international team of scientists says they have compelling evidence that the Huanan Market in Wuhan has been the epicenter from which the Covid pandemic originated. The researchers show that the geographical distribution of the first cases of illness in December 2019 is centered around the market. Most of the patients who were confirmed to have been to the market could be linked to the western market hall of the complex. There were also stalls where (illegal) living mammals were traded.

That writes a team of international virologists led by Michael Worobey of the University of Arizona this weekend in a preprint (a concept not yet reviewed by other scientists).

“A Breakthrough on the Origin of the Pandemic”, tweeted virologist Marion Koopmans of Erasmus MC in Rotterdam. Koopmans himself is one of the authors of the article. “I think it’s now really very clear that the virus came from wild animals,” she says over the phone. “It’s the accumulation of clues that makes the evidence stronger.”

Primary source

Because the Chinese authorities are not making all the essential data available around the start of the outbreak in Wuhan in December 2019, researchers have to dig into the scarce data that exists.

Worobey’s team concludes that the Huanan market was the primary source of the virus, and that it likely spread from wildlife to humans.

The researchers have gone to great lengths to establish a link between the first covid patients and the market. They extracted that information from a card in a March 2021 WHO report with a dot for each patient. The researchers roughly determined the geographic coordinates of the dots and then showed that the density of early patients increased the closer they lived to the market.

However, critics say it can be insidious to conclude from this data that the Huanan market is the source; after all, that spot was already under a magnifying glass when registering patients.

678 shops

On the market itself, the researchers also dug further for the source. They again used a map from the WHO report, this time an overview of the covered market complex with 678 shops. It indicated where the Chinese CDC had found positive environmental samples and where sellers had become ill. The corresponding list was previously leaked through Chinese media, but is now also included in a preprint by a Chinese team led by George Gao. In January 2020, 923 environmental samples were collected on and around the market and 457 samples from animals. The animal samples were negative without exception, but 73 environmental samples did contain SARS-CoV-2. Worobey’s team concludes that positive environmental samples remarkably often coincided with stalls where live wild animals may have been traded. Evidence that they were indeed in those places comes from photos and a list from a publication about illegal wildlife trade in Wuhan.

Gao’s preprint suggests that humans, not animals, were the source. Worobey’s team considers an animal source to be the most likely and focuses in particular on one shop on the south side of the west hall, right in the middle of the zone with the highest probability of a positive environmental sample.

In a response, molecular biologist Alina Chan however, the reliability of this analysis is questionable, as it appears that the environmental samples were not taken randomly throughout the complex.

Another thing is that the most infections were relatively among market traders on the north side of the market (often fishmongers). The Worobey team explains this from the mobility of the people in the market; their location need not have been the place where they became infected. This may have gone through toilets or other public spaces that sellers shared with each other, as other scientists suggest†

From the beginning

The state of affairs after the appearance of all these preprints: the scenario that was considered plausible from the start has become slightly more plausible. That is that the virus was brought from bats to people in the big city via a wild animal as an intermediary. But alternative scenarios, including escape from a lab, remain possible.

Koopmans says the supply lines of both the farmed and wild animals need to be traced back to find more clues. “The raccoon dog is very suggestive,” she says. “We have indications that these animals were traded in the market all year round. That indicates a steady supply, so very different from, for example, wild-caught porcupines that occasionally showed up. Raccoon dogs are susceptible to this virus. But it’s like looking for a needle in a haystack, and maybe the evidence is gone because the farms are no longer there.”