By Victoria Gill and Roland Pease
BBC News and BBC World Service
We now, finally, person "the champion evidence" we are ever apt to find of however the microorganism that causes Covid-19 was archetypal transmitted to a human, a squad of scientists has said.
It's a decision that emerged from the latest technological twist successful the troubled, highly politicised hunt for the origin of the worst pandemic successful a century.
The astir caller investigation points to a peculiar taxon arsenic the apt carnal root of the virus. That decision is based connected grounds that was gathered 3 years agone from the Huanan Wildlife Market successful Wuhan, which has ever been a focal constituent of the archetypal outbreak.
During the aboriginal days of 2020, erstwhile Covid was inactive a enigma disease, the Chinese Centers for Disease Control (CDC) took samples from the market. The familial accusation contained successful those samples has lone precocious been made, briefly, public, and that enabled a squad of researchers to decode them and constituent to racoon dogs arsenic a imaginable "intermediate host" from which the illness spilled implicit into people.
The crux of this investigation is that DNA from racoon dogs, chaotic mammals that were being sold unrecorded successful the marketplace for meat, was recovered successful the aforesaid locations arsenic swabs from the marketplace that tested affirmative for SARS CoV-2, according to an investigation that was published online connected 20 March.
But successful the messy hunt for the outbreak's origin, wherever the marketplace has agelong since closed and immoderate animals connected merchantability killed, we inactive bash not person definitive proof. And the three-year hold successful releasing this captious information has been described by immoderate scientists arsenic "scandalous".
Now, the scientists progressive successful the three-year ngo to analyse Covid's root person told the BBC wherefore this mightiness beryllium the closest we volition get to knowing however the outbreak started. And wherefore the divisions betwixt China and the West are hampering the technological effort to lick that mystery.
What does the caller probe show?
The afloat familial sequences from these important swabs from the marketplace were spotted by Dr Florence Debarre, a elder researcher astatine the Institute of Ecology and Environmental Sciences successful Paris. She told the BBC World Service's Science successful Action that she had been "obsessed" with uncovering this information since she archetypal recovered retired it existed.
Having recovered and downloaded the codes connected a familial database called GISAID, wherever scientists stock this benignant of information, she and her colleagues acceptable retired to find retired which taxon matched the samples that were recovered successful the aforesaid locations arsenic the virus. "We saw the results look connected our screens, and it was: racoon dog, racoon dog, racoon dog, racoon dog," she recalled.
"So we recovered animals and microorganism [together]," explained Dr Debarre. "That does not beryllium that the animals were infected, but that is the astir plausible mentation of what we've seen."
According to Prof Eddie Holmes from the University of Sydney, who was besides progressive successful the study, this is the "best grounds we volition get" of an carnal root of the virus.
"We volition ne'er find that intermediate [animal] big - it's gone," Prof Holmes told the BBC.
"But it's bonzer that the familial information has recovered these ghosts - and it perfectly tells america not conscionable what taxon were there, but precisely wherever they were successful the market," Prof Holmes told the BBC.
What tin scientists bash present to find Covid's origin?
This caller information could supply much leads for further probe into the root of the outbreak, but pursuing those leads volition beryllium complicated.
Prof Marion Koopmans from Erasmus University successful Rotterdam was portion of the World Health Organization investigative squad that went to Wuhan successful 2020. She explained that the caller investigation "pinned their beingness down to circumstantial stalls, truthful you could cheque wherever animals sold determination came from".
"Of people if that is portion of amerciable sales, the question is if you would ever find that out."
There could besides inactive beryllium biologic grounds contiguous successful farms wherever these animals are raised for the trade. If researchers could find farmed animals with antibodies that amusement they had been infected with SARS Cov-2, that could supply different clue. This familial accusation could astatine slightest constrictive down wherever to look.
But uncovering the existent microorganism successful an animal, says Prof Holmes, volition beryllium precise hard.
Does this reply the question of however the pandemic started?
This is not definitive proof. That is thing we mightiness ne'er have.
The hunt for that impervious has itself go heavy politicised and often toxic. While this lends value to the mentation that the microorganism emerged successful chaotic animals and dispersed to humans astatine the market, different mentation has focused connected a imaginable "lab leak" of a microorganism from Wuhan Institute of Virology.
That mentation gained headlines erstwhile again precocious weeks aft an quality appraisal from the US vigor section and Republican-led hearings into the pandemics origins.
In his interrogation with BBC Science successful Action, Prof Holmes pointed to a previous survey of the earliest known cases of Covid successful Wuhan. "The outbreak started astir the market," helium said. "And present we tin spot wherefore - the cardinal animals are there.
"It didn't commencement astir the lab, which is 30km away. And determination is not a azygous portion of information showing immoderate aboriginal cases astir the laboratory."
The years-long hold successful releasing this invaluable information has led to vexation and choler with the China CDC.
"The information are 3 years aged - it's an implicit ungraded that it's taken this agelong for it to spot the airy of day," said Prof Holmes.
The accusation had really been posted onto the GISAID familial database backmost successful February 2022. But it was near determination unnoticed. It's assumed that this was done to supply supporting grounds for a probe insubstantial based connected the information that was being prepared by Chinese researchers from the CDC. (Sharing specified inheritance information is considered a request for technological publication.)
But soon aft the Chinese researchers learned that others had seen the information, it became hidden again.
In a property league connected 17 March, Tedros Adhanom Ghebreyesus, director-general of the World Health Organization (WHO) said that "every portion of data" was important successful moving america person to that answer. "And each portion of information relating to studying the origins of Covid-19 needs to beryllium shared with the planetary assemblage immediately."
"We person to get beyond the authorities and backmost to the axenic science," said Prof Holmes.
He added: "Humans get viruses from wildlife - it's been existent passim our full evolutionary history. The champion happening we tin bash is abstracted ourselves from this wildlife and person amended surveillance.
"Because this volition hap again."