Analysis from the Wuhan market at the centre of one of two leading theories on the origins of Covid has confirmed the presence of genetic material from wild animals that tested positive for the virus.
The results, from swabs taken in January 2020, suggest the pandemic could have started as a zoonotic spillover event, with an animal at the market acting as an intermediate host of the virus between bats and humans. The competing theory suggests a leak from the nearby Wuhan Institute of Virology sparked the global pandemic.
Researchers say that the findings do not provide definitive proof for the animal-to-human spillover theory – while those with concerns about the report note the presence of genetic material from animals unlikely to have been at the market, including pandas, which raises questions over possible contamination.
However, publication of the data and analysis by the Chinese Center for Disease Control and Prevention in the journal Nature will still contribute to helping uncover the origins of Covid, which in a matter of months spread across the globe, killing millions of people.
‘It’s one of the most important data sets we’ve had since the emergence of the pandemic,’ said Florence Débarre, an evolutionary biologist at the French national research agency CNRS in Paris. ‘They exist because at the time the right things were done.’
Since the start of the outbreak, the Huanan market has been at the centre of the zoonotic spillover theory, with several early cases linked to the facility. However, the lab-leak theory has slowly gained momentum, and received a further credibility boost in February when a United States Department of Energy report concluded the virus most likely emerged from such a leak.
The Nature paper included analysis of 172 swaps, with 60 testing positive for SARS-CoV-2, the Covid virus, and 112 negative. The genetic material detected came from a range of animals, including raccoon dogs, a species of interest with potential to transmit the virus. It also detected both of the early strains thought to have been circulating, providing further support for the spillover origin theory.
But just as the results cannot guarantee the event that triggered the global pandemic, they also cannot rule out the possibility that the market simply acted as an amplifier. Speaking to Nature, Stanford University microbiologist David Relman said: ‘It’s just as possible that humans brought the virus into the market, as animals might have.’
Evolutionary virologist Jesse Bloom added: ‘If we ever learn the exact origins of SARS-CoV-2, I suspect it will come from new information about cases or events in early December or November of 2019, or earlier.’
Alice Hughes, a University of Hong Kong conservation biologist, raised concerns over the quality of the paper. The swabs identified genetic material from a range of wild animals, including pandas and chimpanzees.
‘There is absolutely no way any trace of panda could possibly be in that market,’ said Hughes. Killing a panda is punishable by death in China.
‘We must be exceedingly careful with interpreting or putting too much faith in the paper,’ she added, warning the results could be the result of laboratory contamination or improper data processing.
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