On March 4, Florence Débarre, an evolutionary biologist at the French National Center for Scientific Research, happened to be searching that database for information related to the Huanan market when, she said in an interview, she noticed more sequences than usual popping up. Confused at first about whether they contained new data, Dr. Débarre put them aside, only to log in again last week and discover that they held a trove of raw data.
Virus experts had been awaiting that raw sequence data from the market since they learned of its existence in the Chinese report from February 2022. Dr. Débarre said she had alerted other scientists, including the leaders of a team that had published a set of studies last year pointing to the market as the origin.
An international team — which included Michael Worobey, an evolutionary biologist at the University of Arizona; Kristian Andersen, a virologist at the Scripps Research Institute in California; and Edward Holmes, a biologist at the University of Sydney — started mining the new genetic data last week.
One sample in particular caught their attention. It had been taken from a cart linked to a specific stall at the Huanan market that Dr. Holmes had visited in 2014, scientists involved in the analysis said. That stall, Dr. Holmes found, contained caged raccoon dogs on top of a separate cage holding birds, exactly the sort of environment conducive to the transmission of new viruses.
The swab taken from a cart there in early 2020, the research team found, contained genetic material from the virus and a raccoon dog.
"We were able to figure out relatively quickly that at least in one of these samples, there was a lot of raccoon dog nucleic acid, along with virus nucleic acid," said Stephen Goldstein, a virologist at the University of Utah who worked on the new analysis. (Nucleic acids are the chemical building blocks that carry genetic information.)
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Dr. Goldstein, too, cautioned that "we don't have an infected animal, and we can't prove definitively there was an infected animal at that stall." Genetic material from the virus is stable enough, he said, that it is not clear when exactly it was deposited at the market. He said that the team was still analyzing the data and that it had not intended for its analysis to become public before it had released a report.
"But," he said, "given that the animals that were present in the market were not sampled at the time, this is as good as we can hope to get."
The idea that raccoon dogs can transmit SARS is not new: back in 2009, the WIV published a study titled "Angiotensin-converting enzyme 2 (ACE2) from raccoon dog can serve as an efficient receptor for the spike protein of severe acute respiratory syndrome coronavirus".
Raccoon dogs might have been intermediate hosts for severe acute respiratory syndrome–associated coronavirus in 2002–2004. We demonstrated susceptibility of raccoon dogs to severe acute respiratory syndrome coronavirus 2 infection and transmission to in-contact animals. Infected animals had no signs of illness.
Prof. Markus Pfenninger, molecular ecologist at LOEWE TBG and SBiK-F, and Professor of Molecular Ecology at University of Mainz: "The genetic information showed that raccoon dogs are likely susceptible to SARS-COV-2 and that they can potentially transmit it to other animals." The data also show that one of the raccoon dog's membrane proteins binds with higher affinity to the spike protein of SARS-CoV-2 than membrane proteins in their relatives such as foxes and wolves, but also than bats, or Asian pangolins.
"Recently, bats and pangolins have been regarded as potential direct vectors of SARS-CoV-2 to humans," Klimpel says. "Which animal host transferred the coronavirus ultimately to humans is still unresolved. However, our study shows that the raccoon dog is a suitable reservoir host for the coronavirus."
We know that raccoon dogs can get SARS-CoV-2 infections and not look sick; that the virus is better adapted to them than to other animals; that they can transmit it; and that the virus was found in raccoon dog cages at the Wuhan market where the outbreak started.
