Multiple opportunities existed in Wuhan animal markets for ‘spillover into humans’
Covid-19 emerged naturally and is not is the product of an accidental leak from a Chinese laboratory, according to a team of internationally-regarded virologists, following a review of all available evidence.
The finding – the second in a less than a week to declare the virus a natural phenomenon – dismisses the possibility that the virus escaped from a Wuhan laboratory in China, where Sars-CoV-2 was first detected.
It backs up the findings of other experts outlined in a letter to the Lancet medical journal.
The 23 scientists – including Prof Edward Holmes, who first shared the Sars-CoV-2 genetic map known as a genome with Chinese colleagues in January 2020; Wellcome Trust director Sir Jeremy Farrar and leading US virologist Dr Angela Rasmussen – assessed the evidence including genetic indications.
Their findings were released as “a pre-print” study which is due to be submitted to a research journal in coming days.
“There is currently no evidence that Sars-CoV-2 has a laboratory origin . . . There is a substantial body of scientific evidence supporting a zoonotic [animal-to-human] origin for Sars-CoV-2,” they conclude.
The epidemiological history of the virus “is comparable to previous animal market-associated outbreaks of coronaviruses with a simple route for human exposure”, they add.
Contact tracing to markets in Wuhan “exhibits striking similarities” with early spread of the original SARS-CoV virus at markets in Guangdong, China, where it “spilled over into humans”.
By definition, this selects for viruses “able to infect humans”, they noted, whereas “laboratory escapes” known to date have “almost exclusively” involved viruses being investigated because of their known human infectivity”.
The suspicion that Sars-CoV-2 is linked to the Wuhan Institute of Virology “stems from the coincidence that it was first detected in a city that houses a major virological laboratory that studies coronaviruses,” they note.
Covid-19 is the seventh identified coronavirus to have infected humans in the past 20 years that feed off cities such as Wuhan, a heavily-populated travel and commercial hub with multiple animal markets.
Viruses closely related to Sars-CoV-2 have been documented in bats and pangolins in Asia but “a significant evolutionary gap exists” in this instance, they add, so neither can be blamed on the current evidence.
The data shows, however, the Huanan market in Wuhan was “an early and major epicentre of Sars-CoV-2 infection” – with thousands of live wild animals for sale, including high-risk species such as civets and raccoon dogs”.
The possibility of a laboratory accident “cannot be entirely dismissed, and may be near-impossible to falsify” but it is highly unlikely given the number of human-animal contacts “that occur routinely in the wildlife trade,” they note.
A failure now to “comprehensively investigate” the natural origins of Covid-19 would leave the world vulnerable to future pandemics from human actions that “have repeatedly put us on a collision course with novel viruses,” they warn.
Virologist Dr Jonathan Stoye from the Francis Crick Institute in London, who was not part of the review, said the debate surrounding the origins of the orgin of Sars-CoV-2 had become increasingly acrimonious. The failure to find a potential natural host for Covid-19 has spurred “speculative, at times verging on the conspiratorial” theories, but there “ is little or no evidence” for them,” he added.
“The failure to detect a potential natural host has stimulated suggestions by some that the Covid-19 pandemic has resulted from the escape of an engineered virus from a lab in Wuhan, China. However, there is little or no evidence for such an event and lab leak theories remain essentially speculative, at times verging on conspiratorial,” he said.
By contrast, this latest paper “provides a refreshingly clear and reasoned description of the virological events that have taken place during the emergence of the pandemic virus. It makes a strong case for the natural origin of the virus followed by on-going adaptation in humans”.
The continuing evolution of the virus to give new variants “is clearly inconsistent with the notion of a purposely manipulated virus optimised for growth on human cells”, Dr Stoye believed.
While there are still gaps in knowledge that should be explored further, particularly regarding events that occurred before December 2019, “the conclusions reached here seem entirely consistent with those in the WHO report released earlier this year”, he said.