Scientist revisits data on raccoon dogs and Covid, highlighting unknowns

After analyzing genetic data collected from a market in Wuhan in early 2020, a virologist said it was unclear whether the animals for sale there had been infected.

A new study of genetic data from a market in Wuhan, China, said the data did not support the hypothesis that the pandemic started with illegally traded animals, sparking a new debate over the samples that other scientists consider essential pieces of the puzzle of how the coronavirus reached humans.

The new study, which looked at the relative amounts of animal and viral material in swabs taken from surfaces on the market in early 2020, said it was difficult to draw conclusions about whether given samples of the virus came from infected live animals or were simply from accidental contamination.

But several outside experts have said that The analysis, published online this week by study author Jesse Bloom, a virologist at the Fred Hutchinson Cancer Center, could have been affected by a number of unknown variables and decisions about how to filter the data.

For these reasons, they said, the results did little to influence their impression of previous studies. Market samples containing animal and viral genetic material, they said, were consistent with the possibility that an animal there - possibly a raccoon dog - transmitted the virus to people, but did not prove that it had happened.

"I think there's a pretty reasonable chance they caught an infected raccoon dog, but that doesn't prove that that was the origin,” said Frederic Bushman, a microbiologist at the University of Pennsylvania who specializes in analyzing samples like those taken from the Wuhan market, but who was not involved in any of the studies. market. "I don't think Bloom's article changes my thinking that much."

Chinese researchers wrote about market data last year, then made the genetic sequences available this year, allowing a team of international scientists to study them. This team wrote in a report last month that based on the data, they could not conclusively identify an animal that transmitted the virus to humans.

But they said the data confirmed that animals suspected of being susceptible to the virus, such as raccoon dogs and masked palm civets, a small Asian mammal implicated in the SARS outbreak two decades ago, were being sold on the market in late 2019. Many of the first Covid-19 patients also worked or shopped at the market.

Because the market was one of only four places from Wuhan who were selling live animals that could plausibly spread the virus, the scientists said it was unlikely that so many early patients were linked to the market by pure chance. They said the genetic data was also supported by other evidence, including that two early strains of the virus were on the market.

This week's study took a different approach to analyzing gene sequences.

Dr. Bloom investigated whether the amount of genetic material from the virus correlated with the amount of genetic material from susceptible animal species in the samples. If a species on the market was largely responsible for shedding the virus, he said in an interview, he would have expected to see a clear link between the amount of genetic material in the virus and the amount of this species.

< p class="css-at9mc1 evys1bk0">But the study found no such clear correlation. Instead, the strongest correlations involved various fish sold in the market that could not have been infected, an indication that the infected people had probably deposited viral material where the fish was.

Dr. Bloom said the finding suggested the virus, also known as SARS-CoV-2, was widely available on the market by the time swabs were collected in early 2020.

"Similarly, we shouldn't read much about there being a bunch of SAR...