It seems like every day we hear about a new SARS-CoV-2 mutation emerging from somewhere or other – the WHO has even had to come up with a new naming system to cope with all the new variants. And, while we’re pretty certain COVID-19 wasn’t created in a lab, nobody can claim to be totally sure where, why, or how the original novel coronavirus came into existence.
What we can do, however, is prepare for the future. That’s what a team of researchers from the University of California, Berkeley, the Polytechnic University of Milan, and the Massey University of New Zealand has set out to do, in a new analysis published this week in Nature Food which aims to locate the “hot spots” for the next coronavirus to emerge.
How did the coronavirus pandemic start?
Although the exact details of the disease’s beginnings will probably remain unclear for a while, most scientists believe that the current pandemic began when a coronavirus found in horseshoe bats somehow jumped to humans.
Based on this theory, the researchers looked for places in the world where this type of bat-to-human transfer would have the opportunity to occur again. And since it’s still not known whether the virus jumped straight from bat to human or if there was an intermediate host, the researchers had to take into account a wide range of potential carriers among wildlife and livestock.
Scientists have previously found a wide range of coronaviruses in horseshoe bats, including some that are “nearly identical” to SARS-CoV-2, the virus that causes COVID-19. And according to researchers who studied the viruses in bat populations in 2020, there are potentially thousands more out there that have yet to be discovered – though only very few of these will have the ability to jump to humans (known as zoonotic transmission).
What makes somewhere a potential coronavirus hot spot?
Since coronaviruses are found so frequently in horseshoe bats, the researchers decided to restrict their study to the species’ natural range. They analyzed land use patterns at 10,000 randomly generated locations throughout Europe and Asia to identify which areas had the highest potential for human-bat interaction.
A “hot spot” was determined to be a place where bat populations coincided with specific human activity: forest fragmentation (i.e. the breaking up of a large, connected forest into separate smaller forests), raising livestock, and human settlement. The researchers also identified places that are at risk of becoming hot spots in the future as the way humans use the land changes rapidly.
“Land use changes can have an important impact on human health … because they can increase our exposure to zoonotic disease,” said study co-author Paolo D’Odorico, a professor of environmental science, policy and management at UC Berkeley, in a statement. “Every formal land use change should be evaluated… for the potential chain reactions that could impact human health.”
The human activities identified by the researchers increase the likelihood of a coronavirus emerging at a location in multiple ways. An increase in human habitation means more opportunity for the two species to come into contact and infect each other. Similarly, an increase in livestock production provides a coronavirus with plenty of potential intermediate hosts to infect on its way into humans. Finally, an increase in forest fragmentation results in the dying off of species that require the very specific habitats provided by those large contiguous forests. With none of these “specialist” species left in an area, horseshoe bats are free to move in, further increasing the chances of meeting a human.
“By creating conditions that are disadvantageous to specialist species, generalist species [such as the horseshoe bat] are able to thrive,” explained D’Odorico. “While we are unable to directly trace the transmission of SARS-CoV-2 from wildlife to humans, we do know that the type of land use change that brings humans into the picture is typically associated with the presence of these bats who are known to carry the virus.”
Where will the next coronavirus emerge?
The coronavirus behind the current pandemic was first identified in China, and it is there that most of the current hot spots are also located.
“China … exhibits higher levels of human presence in horseshoe bat distributions, as evidenced by population density and the fraction of the landscape covered by villages, towns and other human settlements,” explains the analysis. “In China, regions close to forest fragments are more densely used for livestock production and human settlements … thereby favouring the contact between wildlife and humans either directly or through intermediate animals such as livestock.”
In fact, the researchers found that China is the global hotspot of simultaneously high forest fragmentation, livestock density, and human settlement, making the country uniquely vulnerable to the emergence of new coronaviruses.
In particular, the researchers said, China’s growing demand for meat products and the resulting increase in industrial livestock farming is particularly concerning, since the methods involved in large-scale meat production bring together large populations of animals with low genetic diversity and often suppressed immune systems – perfect for a virus to run rampant.
However, the study also identified many places outside of China that are at risk of becoming hot spots. As forest fragmentation continues in Japan and the north Philippines, the likelihood of these regions seeing their own coronavirus hot spots increases too.
Similarly, parts of Southeast Asia and Thailand are vulnerable to becoming hot spots as humans and livestock take over the natural landscape.
How can we stop a new coronavirus from emerging?
The researchers hope that their analysis will provide insight into how to prevent the emergence of a new coronavirus pandemic.
“The analyses aimed to identify … the type of land use change that could induce hot spot activation,” said study co-author Maria Cristina Rulli, a professor in hydrology and water and food security at the Polytechnic University of Milan. “We hope these results could be useful for identifying region-specific targeted interventions needed to increase resilience to coronavirus spillovers.”
One key recommendation is to try to curb forest fragmentation, creating continuous areas of forest and wildlife corridors so that specialist species can survive. Although China has been a world-leader in tree-planting efforts over the past two decades, they mostly have not been resulting in these large, contiguous forested areas, which the researchers explain are more important than the overall number of trees.
“Human health is intertwined with environmental health and also animal health,” D’Odorico explained. “Our study is one of the first to connect the dots and really drill down into the geographic data on land use to see how humans are coming into contact with species that might be carriers.”