The recent coronavirus outbreak could have started as early as September 2019, scientists have said.
Cases of COVID-19 were believed to have first emerged in December 2019 and were linked to a wet market in Wuhan, China.
However, researchers from the University of Cambridge have now claimed the outbreak could have begun six months ago – and much further south than the central Chinese city of Wuhan.
The scientists made their revelation about the virus’ origin after analysing a large number of strains from around the world.
And they calculated that the initial outbreak occurred in a window between September 13 and December 7 – before going on to infect more than two million people across the world.
University of Cambridge geneticist Peter Forster said: “The virus may have mutated into its final ‘human-efficient’ form months ago, but stayed inside a bat or other animal or even human for several months without infecting other individuals.
“Then, it started infecting and spreading among humans between September 13 and December 7.”
The team analysed the different strains of coronavirus using a phylogenetic network – a mathematical process that can map the global movement of organisms through the mutation of their genes.
They were still trying to pinpoint the exact location of “patient zero”, and were hoping for help from scientists in China.
However, some early signs were prompting them to look into areas to the south of Wuhan, where coronavirus infections were first reported in December.
“What we reconstruct in the network is the first significant spread among humans,” Forster added.
In the new study, which has not been peer-reviewed, the scientists could trace the origin of the virus’ global spread more precisely with every strain they analysed.
By counting the mutations, they could get closer to working out when the first person was infected by a strain that was closest to the first outbreak.
Sars-CoV-2, the virus that causes Covid-19, is believed to have originated from bats.
It has been found to share 96 per cent identical genes with a coronavirus isolated by Chinese scientists from bat droppings in the southwestern province of Yunnan in 2013.
Despite this, there were hundreds of mutations between Sars-CoV-2 and the one in Yunnan, and a coronavirus usually acquires one mutation per month.
Some scientists have therefore suspected the virus may have been spreading quietly in host animals and humans for years to gradually evolve to a highly adaptive form that could infect humans.
According to the Cambridge team, the first outbreak could be a recent event involving the last few mutations that completed the leap from harmless strain to deadly pathogen.
The virus’ origin has become the subject of countless conspiracy theories.
Online rumours have claimed the virus was created in a lab and is the work of the US military, while other wacky webizens allege the outbreak was designed to stop Brexit.
Earlier this week, it was reported that the virus could have originated from a biosafety laboratory in Wuhan.
Despite this, this lab-origin theory has long been dismissed by top scientists across the world due to scientific evidence pointing to a natural origin.
The ongoing Cambridge study could shed more light on the issue.
“If I am pressed for an answer, I would say the original spread started more likely in southern China than in Wuhan,” Forster said.
“But proof can only come from analysing more bats, possibly other potential host animals, and preserved tissue samples in Chinese hospitals stored between September and December.
“This kind of research project would help us understand how the transmission happened, and help us prevent similar instances in the future.”
Su Bing, a genetic researcher with the Kunming Institute of Zoology in Yunnan, said the Cambridge study was eye-opening but their method had its limits.
He revealed that during an unprecedented outbreak, the virus could undergo transformations in unpredictable patterns.
“So it cannot be very precise – there is always a margin for error,” he said.
“This work may provide some important clues to future investigations, but the conclusions should be treated with caution.”