US President Donald Trump has declared that his administration will investigate whether the pandemic coronavirus that has killed more than 170,000 people around the world came from a virus research laboratory in Wuhan, the central Chinese city where the pathogen was first detected.
The announcement on Friday has given new life to unsupported theories that the virus was engineered in the lab, despite repeated denials from the facility and debunking of the suggestions by the mainstream scientific community.
The facility at the centre of the rumours is the Wuhan National Biosafety Laboratory, China's only top-level biosafety facility, run by the Wuhan Institute of Virology and affiliated with the Chinese Academy of Sciences (CAS).
The lab contributed to the genome sequencing and identification of the virus in January, and its database, coordinated by leading virologist Shi Zhengli, helped to quickly link the new coronavirus to a bat virus collected from Yunnan province.
The two viruses have about 96 per cent of their genetic material in common.
In the early days of the outbreak, many of the patients were linked to a wet market in central Wuhan, raising the hypothesis that some species of wild animal, perhaps a pangolin, sold at the market was an intermediate host through which a bat-borne virus made the critical evolution and jumped to humans.
In the weeks that followed, a range of unsubstantiated theories surfaced, including a claim aired on January 25 by Steve Bannon, a former adviser to Trump, that the coronavirus was a biological weapon that had leaked from the institute.
On January 31, a group of researchers from India published a paper on preprint site bioRxiv.org, claiming the coronavirus had some traits similar to the HIV/Aids virus, which was "uncanny" and "unlikely to be fortuitous in nature".
Critics soon questioned the researchers' technical approach and interpretation of results.
The authors withdrew the paper two days later, but not before it was cited by conspiracists as a "proof" that the virus was engineered by humans.
Rumours linking the institute and the coronavirus also took off on Chinese social media, including one in mid-February that a postgraduate student at the institute had been identified as "patient zero" of the epidemic.
In another version, she was already dead from Covid-19, the disease caused by the coronavirus.
The student's supervisor later made a statement saying that the student had not been infected and had not been in Wuhan since she graduated in 2015.
On February 17, the microblog account purportedly belonging to an institute researcher was used to publish a letter accusing the institute's director of leaking the virus.
The account was later confirmed to be fake.
In the United States, one of the biggest promoters of the idea that the institute was responsible for the coronavirus is US Senator Tom Cotton.
"We also know that just a few miles away from that food market is China's only biosafety level-four super laboratory that researches human infectious diseases," he said on Fox News on February 17.
On February 22, researchers from CAS found that the virus samples from the seafood market were genetically "newer" than some from other places, meaning the virus was not originated within the market.
It also cross-confirmed clinical records published in the medical journal The Lancet in late January that some of the earliest cases had no market exposure.
The result again shrouded the origin of the virus and the path to humans in mystery.
Since the coronavirus expanded into a global pandemic in March, the origin of the virus has become a political dispute, rather than a cause for scientific exploration.
Trump has referred to the pathogen as the "Chinese virus" and blamed China for the disease. At the same time, Chinese officials have promoted a narrative the virus could have originated in the US.
But the scientific research continues.
On March 17, Nature published a paper that strongly countered the "bioweapon" theories, concluding that Sars-CoV-2, the official name of the novel coronavirus, is "clearly… not a laboratory construct or a purposefully manipulated virus".
Last week a Washington Post report said some 2018 US diplomatic cables had mentioned concerns over safety and management problems at the Wuhan institute.
Although the report did not elaborate, it again fuelled the discussion on the lab-leak theory.
Soon after, Mark Milley, chairman of the US joint chiefs of staff, said intelligence was looking into the possibility that the coronavirus outbreak could have started in the institute's laboratory.
"It's inconclusive, although the weight of evidence seems to indicate [a] natural [cause of the virus]... But we don't know for certain," Milley said.
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This article was first published in South China Morning Post.