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COVID-19 likely reached humans through the wildlife trade, not direct bat-to-human contact, new research has suggested — mirroring the path taken by the virus behind the 2002 SARS outbreak and challenging theories of a lab-based origin.
Scientists found that the ancestor of SARS-CoV-2 — the virus responsible for COVID-19 — originated in bats from western China or northern Laos and travelled over 2,700 kilometres before the disease was first detected in central China. The findings suggested that the virus did not have enough time to travel such a distance via natural dispersal methods from its primary host: The horseshoe bat.
The study, conducted by researchers at the University of California San Diego School of Medicine and published in the journal Cell on May 7, 2025, provided fresh evidence supporting a zoonotic origin linked to wildlife trade.
Horseshoe bats (Rhinolophus spp.) are recognised as the primary hosts of Sarbecoviruses, a subgenus of the Betacoronavirus genus (family Coronaviridae). These viruses are believed to have spilled over to humans as zoonotic diseases through transmission involving transient intermediate animal hosts, ultimately giving rise to SARS-CoV.
Sarbecoviruses were responsible for both SARS-CoV-1 — the virus behind the 2002–2004 SARS outbreak — and SARS-CoV-2, which caused the COVID-19 pandemic. While these viruses do not appear to harm their bat hosts, how they reached the locations where outbreaks occurred remains unclear. Researchers attempted to analyse the family tree of both viral strains.
To trace the virus's journey, researchers analysed genome sequences to reconstruct the evolutionary history of sarbecoviruses across Asia. However, RNA viruses frequently recombine inside their bat hosts, making evolutionary mapping challenging, found the researchers.
“When two different viruses infect the same bat, sometimes what comes out of that bat is an amalgam of different pieces of both viruses,” said Joel Wertheim, co-author of the paper and professor of medicine at UC San Diego.
Recombination, he added, meant that different parts of a viral genome could follow different evolutionary paths, increasing its complexity. To overcome this, the team focused on non-recombining regions of the genome to trace a clearer lineage.
They found that sarbecoviruses had been circulating for millennia in western China and Southeast Asia, hosted by horseshoe bats. However, these bats typically forage and disperse within a range of just 2-3 kilometres. The sarbecoviruses related to both SARS-CoV-1(now extinct) and SARS-CoV-2 are believed to have similar dispersal capacity. That made it unlikely horseshoe bats could have transported viruses over thousands of kilometres in such short timescales.
The researchers estimated that the most recent ancestors of SARS-CoV-1 and SARS-CoV-2 strains emerged in their regions of origin less than ten years before the viruses began infecting humans — and at locations more than 1,000 kilometres away.
“We show that the original SARS-CoV-1 was circulating in western China just one to two years before the emergence of SARS in Guangdong Province, South Central China, and SARS-CoV-2 in Western China or Northern Laos — just five to seven years before the emergence of COVID-19 in Wuhan,” Jonathan E Pekar, a postdoctoral researcher at the University of Edinburgh, said in a statement.
Given the limited range of horseshoe bats and the need for the strains to cover large distances quickly, researchers concluded that the viruses were likely transported by wild animals traded for meat or fur — serving as intermediate hosts. This aligns with earlier findings that SARS-CoV-1 likely spread from Yunnan Province in Western China to Guangdong Province via infected palm civets or raccoon dogs, commonly sold in live-animal markets.
“However, the current study provides the strongest evidence to date that SARS-CoV-2 made it to humans in a similar manner,” the scientists underlined.
Michael Worobey, professor of ecology and evolutionary biology at the University of Arizona, added that viruses similar to SARS-CoV-2 had previously been found in palm civets and raccoon dogs in southern China—far from the original bat habitats.
“For more than two decades the scientific community has concluded that the live-wildlife trade was how those hundreds of miles were covered. We’re seeing exactly the same pattern with SARS-CoV-2,” he said.
The study also countered the widely circulated theory that, unlike SARS-CoV-1, SARS-CoV-2 leaked from a laboratory.
“At the outset of the COVID-19 pandemic, there was a concern that the distance between Wuhan and the bat virus reservoir was too extreme for a zoonotic origin,” Wertheim said, adding, that this paper shows that it isn’t unusual and is, in fact, extremely similar to the emergence of SARS-CoV-1 in 2002.
The researchers warned that the risk of future zoonotic pandemics is rising due to habitat destruction, urbanisation and the global wildlife trade. Continued monitoring of sarbecoviruses in bat populations, they said, could help identify the next pandemic threat and prepare more effectively for future outbreaks.
