Researchers at China’s Wuhan Institute of Virology have found a new branch in the family tree of bat coronaviruses.
The viruses, described in a preprint paper released last Friday, are more distantly related to the coronavirus that causes Covid-19 than several other known viruses, the researchers said, but have high levels of similarity across certain areas of the genome.
It was the first time that the facility, which has become the centre of unsubstantiated theories that the Covid-19 pandemic could have started from a lab leak, had released details of the viruses, which it collected several years ago.
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“These results suggested the [coronaviruses] we discovered from bats now may be just the tip of the iceberg,” the team wrote in the paper on the server bioRvix.
They also provide new insight into viruses stored by the institute.
The latest research examines eight viruses gathered during a 2015 visit to a town in the southwestern province of Yunnan, where researchers from the Wuhan institute (WIV) collected over 1,000 samples from bats in and around a mining cave over a three-year period.
The work began after several people who had visited the mine fell ill, the researchers have previously said. After tests showed they were not ill with known viruses, they suspected the patients had been infected by an unknown one and began searching the mine for bat viruses. The WIV team has since said that tests showed they were also not infected with Covid-19.
In their research of the cave, the team found nine viruses to be in a category that includes the viruses that cause severe acute respiratory syndrome and Covid-19, the Wuhan researchers said in the journal Nature in November.
One, known as RaTG13, was published by the researchers last February, and remains the closest known relative to Sars-CoV-2, which causes Covid-19. The remaining eight appear to be the viruses categorised in the latest paper.
The origins of Covid-19 remain unknown and highly contentious, over a year after it was first detected in Wuhan in central China.
Some scientists and US government officials have questioned whether the virus could have been the product of a leak from the institute or other Wuhan laboratories studying bat viruses – a charge it has vehemently denied.
Scientists on a World Health Organization-backed field mission to Wuhan earlier this year called this theory “extremely unlikely”. The virus most probably came from an animal such as a bat before passing into humans via another animal in close human contact, a common route for such spillovers, said the team of international and Chinese scientists.
But critics, including the head of the WHO, have said the investigation was not extensive enough to rule out a lab accident. Meanwhile, calls to further examine this possibility have gained steam in recent weeks in the United States, with prominent scientists and lawmakers among those calling for more investigation of the theory.
On Sunday The Wall Street Journal cited a previously undisclosed US intelligence report that found three researchers from the institute fell ill and sought hospital care a month before Wuhan‘s first confirmed cases of Covid-19.
China‘s foreign ministry spokesman Zhao Lijian told a regular briefing on Monday that the report was “totally inconsistent with the facts”.
How the investigation into the origins of the virus should continue is likely to be up for discussion at the meeting of the WHO’s 194 member countries this week.
The Wuhan researchers address “speculation” about a lab leak in their latest paper, but said the “evidence cannot support” the theory since the closest strain in their laboratories, with a 96 per cent similarity to Sars-CoV-2 or decades of evolutionary distance, has a very weak ability to bind to human cells.
The eight newly described viruses, which were highly similar to each other, were at most just over 77 per cent identical across the whole genome to Sars-CoV-2. None were isolated in the lab, the researchers said.
They also could not efficiently bind to a human cell receptor used by other coronaviruses that infect people, according to experiments run on one of the viruses, dubbed RaTG15, indicating little spillover potential without further adaptation.
It’s not clear from the paper why full genetic information about the lineage was not released earlier.
Evolutionary biologist Edward Holmes at the University of Sydney, who was not involved with the work, said the paper provides further evidence that the Wuhan lab does not contain a close enough virus to Sars-CoV-2 for it to have been the source of the Covid-19 outbreak.
“For the ‘lab leak’ allegation against the WIV to be true, this institute must possess a virus that is more closely related to Sars-CoV-2 than RaTG13,” he said, noting the latest viruses are “clearly distant to Sars-CoV-2”.
“It also just really reiterates the amazing diversity of animal coronavirus there are in nature,” said Holmes, who was part of a separate team that found four new bat viruses closely related to Sars-CoV-2 among just over 400 samples also collected in Yunnan.
The region has been singled out by the WHO as an important area for further research into the origins of Covid-19, although it is unclear whether such work is under way.
In the recent paper, the Wuhan researchers said that their work and other recent discoveries highlight the potential for the related coronaviruses to swap parts and further adapt, perhaps via other species, before spreading in humans – a process which could have given rise to Covid-19.
They called for more “systematic and longitudinal sampling” of bats and pangolins.
Pangolins have been found with a coronavirus able to effectively bind to human cells, unlike those in the new lineage and other bat viruses related to Sars-CoV-2 identified so far, according to the Wuhan team.
Maciej Boni, an associate professor at Pennsylvania State University’s Centre for Infectious Disease Dynamics, said that there were likely wide gaps between the newest lineage and viruses closely related to Sars-CoV-2, but currently there were not enough known viruses to see the big picture.
“We need to get to a place where our bat coronavirus database has thousands and thousands of viruses … until we get to thousands of viruses there won’t be a lot of new discoveries about where Sars-CoV-2 came from,” he said.
This article Wuhan laboratory adds another branch to bat coronavirus family tree first appeared on South China Morning Post