Contentious hunt for COVID-19’s origin points to animal trade in China

Scientists tracing the origins of the COVID-19 pandemic believe they’ve identified a possible transmission source: China’s thriving wildlife trade.

The highly anticipated findings from experts convened by the World Health Organization and the Chinese government are expected to show parallels to the 2002 spawning of severe acute respiratory syndrome, or SARS, a batborne coronavirus that was spread by civets and killed 800 people. The path trod by SARS-CoV-2, the coronavirus that causes COVID-19, remains a mystery, though it’s one that researchers say can be solved.

In Wuhan, where the first cluster of cases occurred in December 2019, scientists involved in the hunt identified four hypotheses to explain the virus’ genesis, including two that stoked controversy even as they were deemed unlikely. The idea that the virus was introduced via contaminated food or packaging is one embraced in Beijing, while the Trump administration said it might have been the result of a laboratory accident. But the most plausible theory, say experts involved in the mission, concerns China’s wildlife trade for food, furs and traditional medicine, a business worth about $80 billion in 2016.

Live animals susceptible to coronavirus infection were present at the Huanan food market in downtown Wuhan. It’s possible they acted as conduits for the virus, carrying it from bats — likely the primary source — to humans, says Peter Daszak, a zoologist who was part of the joint research effort, which saw international experts visit Wuhan this year after months of stonewalling by the Chinese government.

“The main conclusion from this stage of the work — and it’s not over yet of course — is that the exact same pathway by which SARS emerged was alive and well for the emergence of COVID,” said Daszak, who is also president of EcoHealth Alliance, a New York-based nonprofit that works to prevent viral outbreaks around the world.

The scientists’ report, slated for release this week after delays due to political wrangling, is likely to be far from conclusive. More studies are planned, including outside China, with deciphering COVID-19’s creation story vital to understanding how best to thwart its resurgence and to help avert similar catastrophes in the future.

While the hunt for the virus’ origin has become a political football for the world’s superpowers, Daszak says he thinks the scientific process will prevail. Significant data on where SARS-CoV-2 came from and how it emerged will be uncovered over the next few years, he said during a March 10 webinar organized by Chatham House.

Farmed and wild-caught civets, a small, nocturnal mammal consumed in China, were blamed for spreading the SARS virus in a market in the southern province of Guangdong in 2003. Scientists later found the infection originated in horseshoe bats, a natural reservoir of coronaviruses.

The two species likely collided in markets where live animals are caged in crowded conditions, potentially allowing the bat-borne virus to adapt and amplify before it spilled over to humans, initially among workers and those handling the animals.

Scientists working on the origin hunt say a similar scenario might have played out with COVID-19. A study of the first 99 patients treated at an infectious-diseases hospital in Wuhan found half were linked to the

Huanan seafood market, which also reportedly sold live animals, some illegally captured in the wild and slaughtered in front of customers.

It’s possible the virus was introduced through an infected animal that was sold at the Huanan market or somewhere else in Wuhan, said Dominic Dwyer, who is a microbiologist in Sydney and was part of the WHO-convened team that traveled to the Chinese city in February.

Still, questions remain about the market’s ultimate role.

Testing after it was shut down in December 2019 failed to turn up any infected animals. Contaminated surfaces were widespread, compatible with the virus being introduced via infected people or tainted animal products. Compounding the confusion, the first known COVID-19 patient developed symptoms four days before the earliest cases tied to the market.

An analysis of SARSCoV-2 samples collected in mid-December found subtle genetic differences between them. The variation indicates the virus might have circulated surreptitiously for weeks in the community before doctors were alerted to it via a handful of severely ill patients.

The original spillover of the coronavirus to a human was probably followed by rapid adaptation of the virus, said Joel Wertheim, an associate professor of medicine at the University of California, San Diego. It’s possible the virus was transmitted multiple times and went extinct when infected individuals didn’t transmit the virus to anyone, Wertheim and colleagues said in a paper published March 18 in the journal Science. Eventually, the virus infected someone who passed it to several people, who also passed it on to others, possibly in a super-spreading event.

The Huanan market might have been where that occurred, Wertheim said.