The Health July/August 2022 - Page 24

Though previous investigations had centred on the live animal market , researchers wanted more evidence

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THE HEALTH | JULY-AUGUST , 2022

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( It is ) critical we continue to study the origins of the # Covid-19 pandemic to ensure that we are better prepared to prevent and mitigate future outbreaks , epidemics and pandemics .”
— Maria Van Kerkhove

New studies point to natural Covid-19 origin

Though previous investigations had centred on the live animal market , researchers wanted more evidence

AN ANIMAL market in China ’ s Wuhan was the epicentre of the Covid pandemic , according to a pair of new studies in the journal Science published on July 26 that claimed to have tipped the balance in the debate about the virus ’ origins .

Answering the question of whether the disease spilled over naturally from animals to humans , or was the result of a lab accident , is viewed as vital to averting the next pandemic and saving millions of lives , according to AFP .
The first paper analysed the geographic pattern of Covid-19 cases in the outbreak ’ s first month , December 2019 , showing the first cases were tightly clustered around Wuhan ’ s Huanan Seafood Wholesale Market . The second examined genomic data from the earliest cases to study the virus ’ early evolution , concluding it was unlikely the coronavirus circulated widely in humans prior to November 2019 .
Both were previously posted as “ preprints ” but have now been vetted by scientific peer review and appear in a prestigious journal .
Michael Worobey of the University of Arizona , who co-authored both 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 him “ to the point where now I also think it ’ s just not plausible that this virus was introduced any other way than through the wildlife trade at the Wuhan market ,” he told reporters on a call .
Though previous investigation had centred on the live animal market , researchers wanted more evidence to determine it was the progenitor of the outbreak , as opposed to an amplifier .
This required neighbourhood-level study within Wuhan to be more certain the virus was “ zoonotic ” – that it jumped from animals to people . The first study ’ s team used mapping tools to determine the location of most of the first 174 cases identified by the World Health Organisation , finding that 155 of them were in Wuhan .
Further , these cases clustered tightly 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 , hog badgers and raccoon dogs – were all sold live in the market , the team showed .
Two introductions to humans
The study authors also tied positive samples from patients in early 2020 to the western portion of the market , which sold live or freshly butchered animals in late 2019 . The tightly confined early cases contrasted with how it radiated throughout the rest of the city by January and February , which the researchers confirmed by drilling into social media check-in data from the Weibo app .
“ This tells us the virus was not circulating cryptically ,” Worobey said in a statement .
“ It really originated at that market and spread out from there .”
The second study focused on resolving an apparent discrepancy in the virus ’ early evolution . Two lineages , A and B , marked the early pandemic .
But while A was closer to the virus found in bats , suggesting the coronavirus in humans came from this source and that A gave rise to B , it was B that was found to be far more present around 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 a timeline of evolution – and found it unlikely that A gave rise to B .
“ Otherwise , lineage A would have had to have been evolving in slow motion compared to the lineage B virus , which just doesn ’ t make biological sense ,” said Worobey .
Instead , the probable scenario was that both jumped from animals at the market to humans on separate occasions , in November and December 2019 . The researchers concluded it was unlikely that there was human circulation prior to November 2019 .
Under this scenario , there were probably other animal-to-human transmissions at the market that failed to manifest as Covid cases .
“ Have we disproven the lab leak theory ? No , we have not . Will we ever be able to know ? No ,” said co-author Kristian Andersen of The Scripps Research Institute .
“ But I think what ’ s really important here is that there are possible scenarios and they ’ re plausible scenarios and it ’ s really important to understand that possible does not mean equally likely .”
The WHO ’ s technical lead for Covid , Maria Van Kerkhove , welcomed the studies ’ publication in a tweet .
“( It is ) critical we continue to study the origins of the # Covid-19 pandemic to ensure that we are better prepared to prevent and mitigate future outbreaks , epidemics and pandemics ,” she said . — The Health