The long-running debate over the origins of covid-19 took another turn this week, after a French scientist spotted that genetic sequences put on a database by Chinese researchers suggest that the coronavirus responsible might have come from animals such as raccoon dogs at the Huanan Seafood Market in Wuhan.
Within a few days, the sequences were removed by the same researchers – although some other scientists managed to download them beforehand and are investigating further.
“It is really critical that any and all data that relates to how this pandemic began be made available immediately,” Maria Van Kerkhove at the World Health Organization (WHO) said at a press conference on 17 March.
“There are several hypotheses that need to be examined, including how the virus entered the human population, either from a bat, through an intermediate host or through a breach in biosecurity from a lab. And we don’t have a definitive answer.”
The Huanan market has long been seen as a probable origin for the SARS-CoV-2 coronavirus, as many of the first cases of covid-19, in December 2019, were in people with a connection to it and the stalls sold a range of live and dead animals, not just seafood.
SARS-CoV-2’s original host is thought to be bats, as they carry many coronaviruses, although they haven’t yet been found with SARS-CoV-2. The ancestor of this virus may have jumped from bats to an intermediate host sold at the market, and then to people.
An alternative explanation is that the virus escaped from the Wuhan Institute of Virology, where researchers were known to be studying bat coronaviruses, but not SARS-CoV-2. While this is a less-favoured idea among scientists, in February, the US Department of Energy said it was the most likely explanation, but didn’t release supporting evidence.
Now, genetic sequences uploaded onto a global virology database called GISAID by the Chinese Center for Disease Control and Prevention may have shed more light on SARS-CoV-2’s origin. These sequences were derived from swabs taken from various surfaces at the market in early 2020 after it had been shut down.
They were noticed by Florence Débarre at the French National Centre for Scientific Research, who shared her findings with the WHO on 14 March. “I was focusing on market sequences when I logged in, but I was not expecting to find the data I found,” says Débarre.
Débarre declined to say any more until her analysis is complete, but Van Kerkhove said at the press conference: “Amongst the samples that were positive for SARS-CoV-2, they saw evidence of DNA of animals. Some of these animals include raccoon dogs.”
Raccoon dogs (Nyctereutes procyonoides) have previously been found to be susceptible to SARS-CoV-2 and to be capable of spreading it. “We know they are good at carrying it,” says Alice Hughes at the University of Hong Kong.
This doesn’t prove that raccoon dogs or any of the other animals at the market were infected with the virus in December 2019 and such evidence is now impossible to source, says Hughes.
Jonathan Stoye at the Francis Crick Institute in London says: “The data would appear to provide convincing evidence that raccoon dogs and other animals were present at the market at a critical time. This is another link in the chain that you would expect to see if the pandemic started that way.”
Off the back of the information Débarre shared, Van Kerkhove said that the WHO has asked the Chinese Center for Disease Control and Prevention to rerelease the genetic data. “The big issue is that this data exists and that it is not readily available to the international community, not to mention that it should have been made available years earlier.”