Researchers behind a new study have concluded that the COVID-19 pandemic was sparked by wildlife trade in China, similar to the circumstances that led to the SARS outbreak in 2002. The results undermine the widely circulated (and much contested) view that the virus was manufactured in a lab.
The analysis shows that the ancestor of SARS-CoV-2, the virus that causes COVID-19, originated in Western China or Northern Laos and then left there several years before the disease appeared in humans in central China. This means that the virus traveled up to 2,700 kilometers (1,678 miles) in a pretty short time – too fast for it to be accounted for by natural dispersal via its primary hosts, horseshoe bats.
SARS-CoV-2 is just one strain of a group of respiratory viruses, known as sarbecoviruses, that are mainly hosted by horseshoe bats. This group also includes the viral strain responsible for the 2002 to 2003 SARS outbreak, SARS-CoV-1.
These viruses do not harm the bats themselves, but can transfer to humans, in whom they cause disease, through a process known as “zoonotic spillover”. As we have seen, this can lead to pandemic events, but it is still not completely clear where exactly this transfer occurred or whether animals other than bats were involved.
To find out, Joel Wertheim, a professor of medicine at UC San Diego School of Medicine’s Division of Infectious Diseases and Global Public Health, and colleagues analyzed the genome sequence data of both SARS-CoV-1 and 2. This allowed them to map the viruses’ evolutionary history across Asia prior to their emergence in humans.
This is not an easy process.
“When two different viruses infect the same bat, sometimes what comes out of that bat is an amalgam of different pieces of both viruses,” Wertheim explained 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.”
To skirt around this problem, the team instead identified and used all of the non-recombining regions of the viral genomes to make their viral family tree.
This map revealed that sarbecoviruses related to SARS-CoV-1 and Sars-CoV-2 have circulated around Western China and Southeast Asia for thousands of years, moving around these regions at similar rates to their hosts.
“Horseshoe bats have an estimated foraging area of around 2-3 [kilometers (1.2 to 1.9 miles)] and a dispersal capacity similar to the diffusion velocity we estimated for the sarbecoviruses related to SARS-CoV-2,” Simon Dellicour, co-senior author and head of the Spatial Epidemiology Lab at Université Libre de Bruxelles and visiting professor at KU Leuven, added.
The research also showed that the most recent ancestors to these two strains left their original homes less than 10 years before they first appeared in humans.
“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 study author Jonathan E. Pekar, a 2023 graduate of the Bioinformatics and Systems Biology program at UC San Diego School of Medicine and now postdoctoral researcher at the University of Edinburgh.
Given this information, it is extremely unlikely that these viral strains could have moved that far that quickly via bats. Instead, it is much more likely that they were transported accidentally by wild animal traders via intermediate hosts. Previous research had already suggested that SARS-CoV-1 was originally transported from Yunnan Province in Western China to Guangdon Province by infected palm civets and raccoon dogs, both of which are traded for their fur and meat. This new data provides solid evidence that COVID-19 likely made its way to humans in a similar way.
“The viruses most closely related to the original SARS coronavirus were found in palm civets and raccoon dogs in southern China, hundreds of miles from the bat populations that were their original source,” study author Michael Worobey, professor and head of the Department of Ecology and Evolutionary Biology at The University of Arizona, explained.
“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.”
These findings fly in the face of the claim that COVID-19 was lab grown while SARS was a natural outbreak.
“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.”
SARS and COVID-19 are both examples of zoonotic spillover events, which are becoming more common across the world as human-animal interactions increase due to wildlife trade, increased urbanization, and habitat loss. This research suggests that monitoring sarbecoviruses in bat populations may be a way to indicate where the next potential spillover event could occur, and by understanding the evolutionary history of these viruses and other pathogens, aid in our efforts to combat future outbreaks.
The study is published in Cell.
Source Link: Bat Virus Evolution Suggests COVID-19 Virus Emerged Naturally, Spreading To Humans Through Wildlife Trade
