A study disputes a widely-circulated idea that SARS-CoV2, the virus that causes COVID-19, was the result of a lab leak.

A new study by UC San Diego School of Medicine researchers and their colleagues has found that the common theory of the origins of the COVID-19 pandemic may be incorrect.

The study, published in Cell on May 7, found that the ancestor of the virus that causes COVID-19 left its point of origin in Western China or Northern Laos just several years before the disease first emerged in humans in Central China, up to 6,777 miles away.

That’s not enough time for the evolving virus to have been carried there via the natural dispersal of its primary host, the horseshoe bat, researchers state.

This has led the team to conclude that SARS-CoV-2, the virus that causes COVID-19, instead hitched a ride there with other animals via the wildlife trade, consistent with what happened during the SARS-CoV-1 (SARS) outbreak in 2002.

Horseshoe bats are the main hosts of sarbecoviruses, which give rise to coronaviruses but don’t harm the bats.

To clarify how sarbecoviruses got to where these events occurred and whether animals besides bats were involved, the researchers analyzed the family trees of both viral strains using genome sequence data available online, mapping their evolutionary history across Asia before they emerged in humans.

However, these RNA viruses undergo a large amount of recombination inside their bat hosts, exchanging genetic material.

“When two different viruses infect the same bat, sometimes what comes out of that bat is an amalgam of different pieces of both viruses,” co-senior author Joel Wertheim, professor of medicine at UCSD School of Medicine’s Division of Infectious Diseases and Global Public Health, said in a statement.

“Recombination complicates our understanding of the evolution of these viruses because it results in different parts of the genome having different evolutionary histories.”

The researchers avoided that problem by identifying all of the non-recombining regions of the viral genomes and using those to recreate the evolutionary history of the viruses instead.

The study found that sarbecoviruses related to SARS-CoV-1 and SARS-CoV-2 have circulated around Western China and Southeast Asia for millennia. During this time, they moved around the landscape at similar rates as their horseshoe bat hosts. 

In contrast, the analysis also revealed that the most recent sarbecovirus ancestors of both SARS-CoV-1 and SARS-CoV-2 left their points of origin fewer than 10 years before they were first reported to infect humans, more than 620 miles away.

Given these distances and the quick rate of coverage, it is highly improbable that they could have been carried there via bat dispersal. Much more likely: they were transported there accidentally by wild animal traders via intermediate hosts.

In fact, previous studies have suggested that SARS-CoV-1, which caused the SARS outbreak, was likely carried from Yunnan Province in Western China to Guangdong Province by infected palm civets or raccoon dogs — animals commonly traded for their fur and meat.

The current study provides the strongest evidence to date that SARS-CoV-2, which causes COVID, made it to humans in a similar manner.

The findings dispute a widely circulated idea that SARS-CoV2 and COVID were the result of a lab leak.

“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. “This paper shows that it isn’t unusual and is, in fact, extremely similar to the emergence of SARS-CoV-1 in 2002.”

Zoonotic spillover events are on the rise globally due to an increase in human-animal interactions via the wildlife trade, according to UCSD, along with urbanization and habitat destruction.

The researchers believe that by continuing to sample wild bat populations for sarbecoviruses, it may be possible to predict where the next coronavirus pandemic will come from.

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