Why are the origins of the pandemic so controversial?

How Covid-19 began has become increasingly contentious, with the US and other allies suggesting China has not been transparent about the origins of the outbreak.

Donald Trump, the US president, has given credence to the idea that intelligence exists suggesting the virus may have escaped from a lab in Wuhan, although the US intelligence community has pointedly declined to back this up. The scientific community says there is no current evidence for this claim.

This follows reports that the White House had been pressuring US intelligence community on the claim, recalling the Bush administrations pressure to stove pipe the intelligence before the war in Iraq.

A specific issue is that the official origin story doesnt add up in terms of the initial epidemiology of the outbreak, not least the incidence of early cases with no apparent connection to the Wuhan seafood market, where Beijing says the outbreak began. If these people were not infected at the market, or via contacts who were infected at the market, critics ask, how do you explain these cases?

Two laboratories in Wuhan studying bat coronaviruses have come under the spotlight. The Wuhan Institute of Virology (WIV) is a biosecurity level 4 facility the highest for biocontainment and the level 2 Wuhan Centre for Disease Control, which is located not far from the fish market, had collected bat coronavirus specimens.

Several theories have been promoted. The first, and wildest, is that scientists at WIV were engaged in experiments with bat coronavirus, involving so-called gene splicing, and the virus then escaped and infected humans. A second version is that sloppy biosecurity among lab staff and in procedures, perhaps in the collection or disposal of animal specimens, released a wild virus.

The scientific consensus rejecting the virus being engineered is almost unanimous. In a letter to Nature in March, a team in California led by microbiology professor Kristian Andersen said the genetic data irrefutably shows that [Covid-19] is not derived from any previously used virus backbone in other words spliced sections of another known virus.

Far more likely, they suggested, was that the virus emerged naturally and became stronger through natural selection. We propose two scenarios that can plausibly explain the origin of Sars-CoV-2: natural selection in an animal host before zoonotic [animal to human] transfer; and natural selection in humans following zoonotic transfer.

Peter Ben Embarek, an expert at the World Health Organization in animal to human transmission of diseases, and other specialists also explained to the Guardian that if there had been any manipulation of the virus you would expect to see evidence in both the gene sequences and also distortion in the data of the family tree of mutations a so-called reticulation effect.

In a statement to the Guardian, James Le Duc, the head of the Galveston National Laboratory in the US, the biggest active biocontainment facility on a US academic campus, also poured cold water on the suggestion.

There is convincing evidence that the new virus was not the result of intentional genetic engineering and that it almost certainly originated from nature, given its high similarity to other known bat-associated coronaviruses, he said.

The accidental release of a wild sample has been the focus of most attention, although the evidence offered is at best highly circumstantial.

The Washington Post has reported concerns in 2018 over security and management weakness from US embassy officials who visited the WIV several times, although the paper also conceded there was no conclusive proof the lab was the source of the outbreak.

Le Duc, however, paints a different picture of the WIV. I have visited and toured the new BSL4 laboratory in Wuhan, prior to it starting operations in 2017- It is of comparable quality and safety measures as any currently in operation in the US or Europe.

He also described encounters with Shi Zhengli, the Chinese virologist at the WIV who has led research into bat coronaviruses, and discovered the link between bats and the Sars virus that caused disease worldwide in 2003, describing her as fully engaged, very open and transparent about her work, and eager to collaborate.

Maureen Miller, an epidemiologist who worked with Shi as part of a US-funded viral research programme, echoed Le Ducs assessment. She said she believed the lab escape theory was an absolute conspiracy theory and referred to Shi as brilliant.

While the experts who spoke to the Guardian made clear that understanding of the origins of the virus remained provisional, they added that the current state of knowledge of the initial spread also created problems for the lab escape theory.

When Peter Forster, a geneticist at Cambridge, compared sequences of the virus genome collected early in the Chines outbreak and later globally he identified three dominant strains.

Early in the outbreak, two strains appear to have been in circulation at roughly at the same time strain A and strain B with a C variant later developing from strain B.

But in a surprise finding, the version with the closest genetic similarity to bat coronavirus was not the one most prevalent early on in the central Chinese city of Wuhan but instead associated with a scattering of early cases in the southern Guangdong province.

Between 24 December 2019 and 17 January 2020, Forster explains, just three out of 23 cases in Wuhan were type A, while the rest were type B. In patients in Guangdong province, however, five out of nine were found to have type A of the virus.

The very small numbers notwithstanding, said Forster, the early genome frequencies until 17 January do not favour Wuhan as an origin over other parts of China, for example five of nine Guangdong/Shenzhen patients who had A types.

In other words, it still remains far from certain that Wuhan was even necessarily where the virus first emerged.

The pandemic has exacerbated existing geopolitical struggles, prompting a disinformation war that has drawn in the US, China, Russia and others.

Journalists and scientists have been targeted by people with an apparent interest in pushing circumstantial evidence related to the viruss origins, perhaps as part of this campaign and to distract from the fact that few governments have had a fault-free response.

The current state of knowledge about coronavirus and its origin suggest the most likely explanation remains the most prosaic. Like other coronaviruses before, it simply spread to humans via a natural event, the starting point for many in the scientific community including the World Health Organization.

Further testing in China in the months ahead may eventually establish the source of the outbreak. But for now it is too early.

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Where did Covid-19 come from? What we know about its origins - The Guardian