Genetic Evidence Ties Covid’s Origin to Raccoon Dogs

A group of scientists say they have new evidence supporting the theory that the Covid-19 pandemic began with a spillover from animals to humans, as opposed to a leak from a lab, the Atlantic’s Katherine J. Wu first reported last week.

Samples taken in early 2020 from the Huanan Seafood Wholesale Market in Wuhan, China, contained both the SARS-CoV-2 virus and genetic material from raccoon dogs, according to a new analysis.

While the research adds new evidence to the mystery of the pandemic’s origin, it is not a smoking gun, experts say. Such a finding “places the virus and the dog in very close proximity,” Michael Imperiale, a microbiologist and immunologist at the University of Michigan who did not contribute to the work, tells Dake Kang and Maria Cheng of the Associated Press (AP). “But it doesn’t necessarily say that the dog was infected with the virus; it just says that they were in the same very small area.”

“We can’t definitively prove that there were infected raccoon dogs who were the first source of the virus going into humans,” Stephen Goldstein, a virologist at the University of Utah who worked on the analysis, tells the Washington Post’s Joel Achenbach and Mark Johnson. “But it is highly suggestive of that.”

The researchers presented their results to a World Health Organization (WHO) scientific advisory group last Tuesday—the findings have not gone through a peer review process, nor have they been published in a scientific journal.

But the new analysis “really strengthens the case for a natural origin,” Seema Lakdawala, a virologist at Emory University who did not contribute to the analysis, tells the Atlantic.

Researchers from the Chinese Center for Disease Control and Prevention quietly uploaded data from the genetic samples taken at the Wuhan market, the site of the first documented Covid-19 outbreak, to an open-access database a few weeks ago, per the Atlantic. The data was recently taken down, but international scientists had already downloaded the data and begun to analyze it.

The samples were collected in animal stalls in early 2020, after the market had been closed, per the Washington Post. Because the samples had raccoon dog genes, scientists think the creatures may have been infected. “There’s a good chance that the animals that deposited that DNA also deposited the virus,” Goldstein tells the AP. “If you were to go and do environmental sampling in the aftermath of a zoonotic spillover event … this is basically exactly what you would expect to find.”

Angela Rasmussen, a virologist at the University of Saskatchewan in Canada who participated in the research, tells the Atlantic, “there’s really no other explanation that makes any sense.”

Still, exactly what caused the Covid-19 pandemic remains uncertain. The FBI has expressed a belief that a lab leak is to blame, and last month, the Department of Energy issued a report that reached the same conclusion, albeit with “low confidence,” per ABC News’ Mary Kekatos. Several labs that collect and study coronaviruses are located in Wuhan. Meanwhile, four U.S. agencies and the National Intelligence Council say the virus likely passed from animals to humans.

Given the possibility of both of these explanations, the new data are “very inconclusive,” David A. Relman, a microbiologist and immunologist at Stanford University who did not contribute to the research, tells the Washington Post in an email. “Frankly, the breathlessness and alacrity with which stories like this one are promoted, in the face of very incomplete and confusing ‘data,’ leaves me frustrated and concerned.”

Several researchers have expressed concerns that information surrounding the pandemic’s origin, such as the recently analyzed genetic data, was not released to the public sooner—or at all. The WHO is asking officials in China to release such data.

“The big issue right now is that this data exists and that it is not readily available,” says WHO epidemiologist Maria Van Kerkhove, according to NPR’s Michaeleen Doucleff and Jason Beaubien. “Any data that exists on the study of the origins of this pandemic need to be made available immediately.”

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Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.