A recent study which found the deadly Covid-19 may have originated in raccoon dogs from the Wuhan market in China, hints that the pandemic may be the result of a spillover from an animal, according to scientists.
The study, now posted on scientific research repository Zenodo and not peer reviewed yet, is based on genetic data drawn from swabs taken from in and around the Huanan Seafood Wholesale Market starting in January 2020.
The swabs were collected in early 2020, after the market was shut down and cleared of animal products, after being linked to the outbreak of Covid pandemic. The researchers got the samples from swabbing walls, floors, metal cages and carts that are used for transporting animal cages.
Besides raccoon dogs, the international team of scientists also found DNA of bamboo rats, palm civets, Malayan porcupine and Amur hedgehog. Their results showed that large amounts of genetic material were a match for the raccoon dog, suggestive of a spill over from an animal.
While the study does not confirm whether the animals themselves were infected with the Covid virus, it does establish that the animals were present at the market. This supports the hypothesis that the pandemic had an animal origin, according to some researchers.
"Of course, this is not direct evidence. But this is the best we can get now, because all the animals have been eliminated from the market and we don't have swabs of the animals," Leo Poon, a virologist at the University of Hong Kong, was quoted as saying in a report in the journal Nature.
However, some researchers said the analysis "falls short of definitive proof," as they did not find an infected animal. The work confirms the animal species that were at the market, but because it includes only samples that had tested positive, "there is no data in this work associating SARS-CoV-2 with the presence of any of these animals", Justin Kinney, a quantitative biologist at Cold Spring Harbor Laboratory in New York, was quoted as saying.
"These data do not provide a definitive answer to the question of how the pandemic began," said Tedros Adhanom Ghebreyesus, Director-General of the World Health Organization (WHO), at a recent press event.
"But every piece of data is important in moving us closer to that answer," he said. "These data could have -- and should have -- been shared three years ago," he said, while rebuking China for hiding such crucial information from the rest of the world for three years.
Meanwhile, the data used for the analysis was discovered almost by chance on the public data repository GISAID on March 4, by Florence Debarre, an evolutionary biologist at the French National Centre for Scientific Research, who is also a co-author on the latest report.
"Basically, (they're) the ones we've been waiting for, for a year," she was quoted as saying. In total, Debarre and her colleagues downloaded around half a terabyte of genomic data from some 50 samples.
But soon after, it disappeared from public view on GISAID. Debarre and her colleagues say they reached out to authors of the preprint to collaborate on the analysis, but the China CDC declined.
The researchers said many more forensic insights could still come from the data if they were made public again. "We continue to call on China to be transparent in sharing data, and to conduct the necessary investigations and share the results," Ghebreyesus said last week.