A pair of new studies point to a natural origin of Covid
Washington (AFP) – An animal market in China’s Wuhan has truly been the epicenter of the Covid pandemic, according to two new studies in the journal Science published Tuesday that claim to have tipped the scales in the debate over the origins of the virus.
Answering the question of whether the disease spread naturally from animals to humans, or whether it was the result of a laboratory accident, is considered essential to averting the next pandemic and saving millions of lives.
The first article analyzed the geographical distribution of Covid cases during the first month of the outbreak, December 2019, showing that the first cases were tightly clustered around the Huanan market.
The second looked at genomic data from early cases to study the early evolution of the virus, concluding that the coronavirus was unlikely to have circulated widely in humans before November 2019.
Both were previously published as “preprints”, but have now been approved by scientific peer review and appear in a prestigious journal.
Michael Worobey of the University of Arizona, co-author of the two papers, had previously called on the scientific community in a letter to be more open to the idea that the virus was the result of a lab leak.
But the findings moved it “to the point where now I also think it’s just not plausible that this virus was introduced other than through the wildlife trade in the Wuhan market,” he said. he told reporters on a call about the findings.
Although the previous investigation focused on the live animal market, the researchers wanted more evidence to determine that it was really the ancestor of the outbreak, as opposed to an amplifier.
This required a neighborhood-level study in Wuhan to be more certain that the virus was “zoonotic” – that it jumped from animals to humans.
The team in the first study used mapping tools to determine the location of the first 174 cases identified by the World Health Organization, finding that 155 of them were in Wuhan.
Moreover, these cases clustered closely around the market – and some early patients with no recent history of visiting the market lived very close to it.
Mammals now known to be infectable with the virus – including red foxes, badgers and raccoon dogs – were all sold alive in the market, the team showed.
Two introductions to man
They also linked positive samples from patients in early 2020 to the western part of the market, which sold live or freshly slaughtered animals in late 2019.
The first tightly contained cases contrasted with how it radiated across the rest of the city in January and February, which researchers confirmed by mining social media registration data from the Weibo app.
“This tells us that the virus was not circulating in an encrypted manner,” Worobey said in a statement. “It was really born in that market and spread from there.”
The second study focused on resolving an apparent discrepancy in the early evolution of the virus.
Two lineages, A and B, marked the start of the pandemic.
But while A was closer to the virus found in bats, suggesting that the coronavirus in humans came from this source and that A gave rise to B, it was B that was found to be much more present on the market.
The researchers used a technique called “molecular clock analysis”, which relies on the rate at which genetic mutations occur over time to reconstruct an evolutionary timeline – and found it unlikely that A gave birth to b.
“Otherwise, the A line would have had to evolve in slow motion compared to the B line virus, which just doesn’t make biological sense,” Worobey said.
Instead, the probable scenario was both passed from market animals to humans on separate occasions, in November and December 2019. The researchers concluded that it was unlikely that there was human circulation before November 2019.
In this scenario, there were likely other animal-to-human transmissions in the market that did not manifest as Covid cases.
“Have we disproved the lab leak theory? No, we didn’t. Will we ever know? No,” said co-author Kristian Anderson of the Scripps Research Institute.
“But I think what’s really important here is that there are possible scenarios and they are plausible scenarios and it’s really important to understand that possible doesn’t mean equally likely.”
© 2022 AFP