Two years in, there is no doubt the Covid pandemic began in the Chinese city of Wuhan. But there is also little doubt that the bat carrying the progenitor of the virus lived somewhere else.
Central to the mystery of Covid’s origin is how a virus normally found in horseshoe bats in caves in the far south of China or south-east Asia turned up in a city a thousand miles north. New evidence suggests that part of the answer might lie in Laos.
The search for viruses closely related to Sars-CoV-2 took a new turn in September when a team of French and Laotian scientists found one in a horseshoe bat living in a cave in the west Laotian province of Vientiane. Other related viruses had been found in Cambodia, Thailand, Japan and elsewhere in China, but this one, Banal-52, was different. For the first time since the pandemic began, this was a virus genetically closer to the human Sars-CoV-2 virus than one called RaTG13, collected in southern Yunnan in 2013. RaTG13, which had been stored for six years in a freezer in a lab in Wuhan itself, is genetically 96.1 per cent the same as Sars-CoV-2; Laos’s Banal-52 is 96.8 per cent.
The discovery of Banal-52 was greeted with relief by champions of the theory that the virus must have jumped into people in a natural spillover event, not an accident inside a laboratory. If Covid’s closest cousins are flitting about in bats in south-east Asia, then that sample in the freezer in Wuhan looks less suspicious. ‘I am more convinced than ever that Sars-CoV-2 has a natural origin,’ said Linfa Wang of Duke-NUS Medical School in Singapore, a close collaborator of the Wuhan scientists.
True, the Laos virus lacked a critical feature in a key part of a key gene that makes Covid so infectious: a special 12-letter segment of genetic text called a furin cleavage site.