A new genetic study bolsters the theory that COVID-19 originated from the wildlife trade, challenging claims of a lab leak. Researchers traced the virus's origins to animals sold in Wuhan markets, adding fuel to the ongoing debate amid US-China tensions.
The findings, published in Cell on May 7, 2025, point to a natural spillover, highlighting the persistent risks of zoonotic diseases stemming from the wildlife trade.
Researchers at the University of California San Diego School of Medicine and their colleagues concluded that the ancestor of SARS-CoV-2, the virus that causes COVID-19, emerged just years before the pandemic began. The virus left its origin in Western China or Northern Laos just years before the emergence, travelling nearly 2,700 kilometres to Central China. This timeframe is too short for natural dispersal by its primary host, the horseshoe bat, suggesting it "hitched a ride" via the wildlife trade, similar to the SARS outbreak in 2002.
"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 co-senior author Joel Wertheim, PhD, a professor of medicine at UC San Diego School of Medicine's Division of Infectious Diseases and Global Public Health. "Recombination complicates our understanding of the evolution of these viruses because it results in different parts of the genome having different evolutionary histories."
To overcome this, the researchers focused on non-recombining regions of the viral genomes, allowing them to more accurately reconstruct the evolutionary history.
The study indicates that sarbecoviruses related to SARS-CoV-1 and SARS-CoV-2 have circulated around Western China and Southeast Asia for millennia, spreading at similar rates as their horseshoe bat hosts.
"Horseshoe bats have an estimated foraging area of around 2-3 km and a dispersal capacity similar to the diffusion velocity we estimated for the sarbecoviruses related to SARS-CoV-2," said co-senior author Simon Dellicour, Ph.D., head of the Spatial Epidemiology Lab at Université Libre de Bruxelles and visiting professor at KU Leuven.
The analysis further revealed that the most recent sarbecovirus ancestors of both SARS-CoV-1 and SARS-CoV-2 left their points of origin less than 10 years before infecting humans more than a thousand 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," said Jonathan E. Pekar, PhD, a 2023 graduate of the Bioinformatics and Systems Biology programme at UC San Diego School of Medicine, now a postdoctoral researcher at the University of Edinburgh.
