New Delhi: New genetic evidence discovered from Huanan Seafood Wholesale Market in China’s Wuhan, where the first Covid cases were identified in late 2019, shows that the virus likely spread from animals, not from a lab, scientists said.
The findings, presented to a World Health Organization-convened advisory group last week, may prove to be an important piece of the puzzle for the pandemic’s origination.
According to an official WHO press release, experts who evaluated genetic data from Wuhan Market Covid samples discovered the presence of raccoon dogs’ DNA (a fox-like species belonging to the Canidae family of mammals). It suggested that the animals — known to be susceptible to the SARS viruses — were being sold in the market.
The WHO addressed these concerns in a briefing on 17 March. “WHO was made aware of new SARS-CoV-2 sequences and metagenomics data associated with samples collected in the Huanan Seafood Wholesale Market, Wuhan, China, from January 2020, that became available on Global Initiative on Sharing Avian Influenza Data (GISAID) for a short period of time. The data had subsequently been downloaded by a number of researchers from several countries. Access was restricted shortly after, apparently to allow further data updates by China CDC,” WHO Director-General Tedros Adhanom Ghebreyesus said.
The details of the international analysis were first reported on Thursday by The Atlantic.
Earlier reports from a US Department of Energy investigation found that the pandemic was the consequence of a laboratory leak, sparking a heated debate about the epidemic’s origins.
Possible identification of intermediate hosts
According to the report, experts at the Chinese Institute for Disease Control and Prevention (CDC) submitted new data from swab samples collected in January 2020 from the market’s floors, walls, and animal cages to the public global genome sequencing database GISAID.
The worldwide team, composed of virologists and biologists, then downloaded and evaluated the samples. Access has now been restricted. The samples that tested positive for the virus also contained genetic material from multiple animals, including significant amounts of raccoon dog.
The report indicates that animals were present at the market shortly before it was cleared on 1 January, 2020, as part of Chinese authorities’ public health measures. These findings could lead to the identification of SARS-CoV-2 intermediate hosts and potential human infection sources in the market.
The detailed study found that, out of 1,380 samples collected from the environment and animals within the market in early 2020, 73/923 environmental samples tested positive for SARS-CoV-2-specific virus from various stalls and sewerage systems in and around the market, but no virus was detected in the 457 animal samples tested.
The animal samples covered 18 species, including animal bodies, frozen animal carcasses, and animal products, as well as stray animals around the market. The Raccoon dogs, according to the study, were not among the animals tested. According to the WHO briefing, the presence of high levels of raccoon’s mitochondrial DNA in the metagenomics data from environmental samples identified in the new analysis suggests that the dogs and other animals were present before the market was cleaned as part of the public health intervention.
The UN agency said it was aware of data uploaded to the GISAID database in late January and subsequently removed. Although this does not establish conclusively that the virus went from raccoon dogs to humans, it is the greatest evidence to date for the natural transmission idea, according to the study.
Delay in disclosure of information
Florence Débarre, an evolutionary biologist at the French National Center for Scientific Research, discovered the genetic sequences of the virus that researchers in China, led by former CDC head George Gao, had uploaded to the GISAID, Scientific American reported.
The sequences were subsequently removed, but not before they were downloaded and analysed by a number of researchers from various nations.
The genetic material found in the same areas as SARS-CoV-2 suggested that the raccoon dogs may have been infected with the virus – possibly by other animals – which was later transmitted to humans.
The global pandemic, which has killed close to seven million people, is still a concern, and no concrete evidence has yet been provided that it spread due to a natural spillover from wildlife to humans or a lab leak from a Wuhan facility researching coronaviruses.
The new evidence, too, does not prove definitively that SARS-CoV-2 jumped from infected raccoon dogs to humans, but it adds to a growing body of evidence in favour of animal transmission. The findings have been sent for further evaluation.
The scientific community has been perplexed by the delay in disclosing information from samples taken more than three years ago. In the press briefing, WHO chief Tedros urged China to release additional information on the Covid-19 study.
(Edited by Tarannum Khan)
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