The inside story of how a scientist concluded covid started as an overflow in the Wuhan wet market


“The penalties for violators can be severe,” says Zhou Zhaomin, an expert on China’s wildlife trade policy at China West Normal University in Nanchong. Those who trade in protected species can face up to 15 years in prison, and bringing them in or out of China in sufficient numbers could result in a life sentence.

But law enforcement was poor. Several researchers told MIT Technology Review that it is “an open secret” that the illegal wildlife trade is rampant in China.

Indeed, Zhou and his colleagues conducted a survey between 2017 and 2019, which found that four markets in Wuhan, including Huanan, sold a combined total of nearly 48,000 wild animals of 38 species, almost all sold alive, caged and stacked in cramped and unsanitary conditions, perfect for virus transmission. Animals – whether captured from the wild or non-domesticated farmed species – include species susceptible to both SARS-CoV-1 and SARS-CoV-2, such as civets, mink, badgers and raccoon dogs.

This study, published in June in Scientific reports, found that all of the wildlife trade the researchers studied was illegal. Many vendors were selling protected species; none displayed the required certificates indicating the origin of the animals or that they were disease free.

This means that as soon as Huanan was implicated in the first cases of covid-19, vendors selling live mammals, most likely illegally, would run away to avoid being jailed, while law enforcement would not admit. probably not that such activities have ever existed. Considering this, it was not surprising that Chinese authorities could not find any leads regarding sales of live animals in the Huanan market, says Harvard’s Hanage.

Restrictions on the wildlife trade were minimal in the aftermath of SARS, giving scientists nearly unlimited access to animals and traders in Guangdong’s wet markets, but even that wasn’t enough to help them. identify the source of SARS. While they quickly became aware of the viruses in civets, badgers and raccoon dogs that were more than 99% identical to SARS-CoV-1, subsequent investigations did not reveal widespread circulation of the virus, either in the wild or under farming conditions. A dominant opinion is that civets caught the virus during trade, probably bats bought and sold at the same time.

Today, 18 years later, the situation is surprisingly similar. It seems to have no widespread circulation of SARS-CoV-2 in animals. None of the roughly 80,000 samples tested by the Chinese team of the World Health Organization mission to research the origins of the pandemic, including prime suspects such as pangolins, civets, badgers and rats from bamboo, did not contain the virus.

Nonetheless, many scientists still lean strongly towards the theory that wet markets played a critical role in triggering covid-19. Even though all eyes are on Yunnan and other parts of Southeast Asia as the most likely places of the pandemic’s origins, Hanage says “it’s not crazy” to suggest that the province from Hubei to Wuhan could have been the place where SARS-CoV-2 naturally emerged.

Indeed, scientists from the Wuhan Institute of Virology have discovered SARS-like coronaviruses in bats in Hubei. While they have not systematically tested farm animals for coronavirus infection across the province, in an unknown study carried out in the aftermath of SARS, they discovered that the seven civets they had tested on a farm in the province in 2004 were all infected with relatives of SARS-CoV-1. Several research teams in China and the United States are trying to determine where animals contracted the virus, whether coronavirus infection in civets is more common than previously thought, and what impact it could have on our understanding the origins of covid-19.

Constant overflow

But without proof of an animal infected with a coronavirus that is more than 99% identical to SARS-CoV-2, some scientists have continued to oppose natural origins.

One such reviewer is Alina Chan, a molecular biologist at the Broad Institute at MIT and Harvard (this publication is owned by MIT, but editorially independent of it). The central question, she said in a recent webinar hosted by Science magazine, this is how the virus arrived in Wuhan from caves over a thousand kilometers away in China or other parts of Southeast Asia. “There is a very strong channel of scientists in Wuhan who go to these places where they [knew] they would find SARS viruses, bringing them to the city of Wuhan, thousands of kilometers away, ”she said. There is no evidence, however, of such routes for the wildlife trade, she adds.

Such a lack of clarity also affects the origins of SARS, says Linfa Wang, director of the emerging infectious diseases program at Duke-National University Singapore. The cave that produced the closest bat relative of SARS-CoV-1 is nearly 1,000 miles from the Guangdong market where the first cases of SARS appeared, similar to the distance from Wuhan to the site where one of the closest relatives of SARS-CoV -2 bats has been discovered.

And it’s increasingly clear that people in close contact with wildlife are infected with coronaviruses much more frequently than previously thought.

“[Huanan] is much more likely than other scenarios based on what we now know. “

Michael Worobey

Studies show that up to 4% of people who live near bats and work closely with wildlife in southern China have been infected with deadly animal viruses, including coronaviruses. A Laotian and French team, who discovered the closest relatives of SARS-CoV-2, found this one in five bat handlers in Laos had antibodies to these coronaviruses.

The majority of these spillover infections go away on their own, researchers say. In a study published in Science in April, Worobey and colleagues show by computer simulation that for the SARS-CoV-2 overflow to trigger major epidemics, an urban setting is essential – without it, it would die out very quickly.

“That’s hundreds, if not thousands of times more likely” than a wildlife trader who was exposed to an ancestor of SARS-CoV-2 – from bats or some other animal species – brought contagion to Huanan that a researcher who went to collect bat samples, they returned to Wuhan with the pathogen, then brought it to Huanan, Wang said.

Worobey agrees. Based on ample evidence, he is now convinced not only that the pandemic’s link to the Huanan market is real, but that it is where an ancestor of SARS-CoV-2 grew from animal to animal. the man. “It’s much more likely than any other scenario based on what we know now,” he says.

The preliminary results of the ongoing work of his group and others will help to further strengthen the case, he adds: “They are all pointing in the same direction.”

Reporting in this article was supported by a grant from the Pulitzer Center.


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