A recent study has provided fresh evidence supporting the theory that Covid-19 first spread to humans from infected animals at the Huanan Seafood Market in Wuhan, China, in late 2019. The research, published in Cell journal, is based on more than 800 samples collected from market surfaces in January 2020, shortly after the market was closed.

The origins of Covid-19 remain disputed nearly five years after the first cases were detected in Wuhan. The global scientific community remains divided between two main hypotheses: that the virus either leaked from a nearby laboratory or was transmitted to humans from infected wild animals. While the animal origin theory has generally been favored, the debate continues.

The new study, co-authored by evolutionary biologist Florence Debarre from France’s CNRS research agency, confirms the presence of wild animals such as raccoon dogs and civets at the market at the time of the outbreak. The research found significant traces of SARS-CoV-2, the virus responsible for Covid-19, in several market stalls, including those selling wildlife. Notably, these samples contained more mammalian DNA than human DNA, suggesting the virus may have been present in the animals.

Though the samples were not taken directly from animals, the study reinforces the idea that raccoon dogs and civets, both known to carry viruses similar to SARS-CoV-2, could have served as an intermediary host between humans and bats, in which the virus likely originated.

While the study cannot conclusively confirm the animals were infected, James Wood, an infectious disease expert from Cambridge University, called it “very strong evidence” that wildlife stalls in the Huanan market were a key site for the virus’s emergence.