In late 2019, Chinese colleagues of Oxford University wildlife biologist and co-author Chris Newman reported seeing a number of wild mammals for sale at the Huanan market. Dr. Holmes said that any of them could have caused the pandemic.

The Raccoon Dogs Are “Certainly a Suspect,” He Said, “But You Can’t Prove Them Yet.”

Critics have questioned Dr. Holmes’ and his colleagues’ ability to be certain that a Huanan animal was responsible. However, it’s possible that there are other cases of pneumonia that haven’t been recognised as early Covid infections.

Expert on biosecurity at King’s College London, Filippa Lentzos, said, “We still know far too little about the earliest cases — and there are likely additional cases we do not know about” to draw final conclusions. For me, both natural and research-related origins are possible.

Another issue is that if infected animals did in fact start the pandemic, no one will ever find out who they are. The Chinese C.D.C. arrived at the market in January 2020 to investigate and found that all of the animals had been slaughtered.

There is, however, ample evidence to support Dr. Holmes’ claim that animal markets could lead to another pandemic. After conducting research on 18 commonly sold animal species in China and the United States, he and his Chinese colleagues recently published a study.

Dr. Holmes Described Them as Being “Completely Infected” With Various Viruses.

More than 100 viruses that can infect vertebrates, including some that could be dangerous to humans, have been discovered. Bird flu infected badgers, and canine coronaviruses were recently found infecting raccoon dogs, for example. Human viruses had infected some of the animals as well.

Dr. Holmes has argued that the simplest way to reduce the likelihood of future pandemics is to conduct studies like this one at the human-wildlife interface. Because of his own discoveries of new viruses, he’s come to the conclusion that trying to catalogue every possible threat in wildlife is pointless.

If you sampled every virus out there, you’d never know which one could infect humans, said Dr. Holmes. “I don’t see how that could work.”