Global land-use changes through human settlement, agricultural expansion and livestock production are creating hot spots favourable for coronavirus-carrying bats, and where conditions are ripe for diseases to jump from the flying mammals to humans, according to a study.
While the exact origins of the SARS-CoV-2, the virus that causes COVID-19, remain unclear, scientists believe that the disease likely emerged when a virus that infects horseshoe bats was able to jump to humans.
It could have done so either directly through wildlife-to-human contact or indirectly by first infecting an intermediate animal host, such as the pangolin.
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Horseshoe bats are known to carry a variety of coronaviruses, including strains that are genetically similar to ones that cause COVID-19 and severe acute respiratory syndrome (SARS).
The new study, published in the journal Nature Food, used remote sensing to analyse land use patterns throughout the horseshoe bat's range, which extends from Western Europe through Southeast Asia.
The researchers analysed the areas of forest fragmentation, human settlement and agricultural and livestock production, and compared these to known horseshoe bat habitats.
By doing so, they were able to identify potential hot spots where habitat is favourable for these bat species, and where these so-called zoonotic viruses could potentially jump from bats to humans.
The researchers noted that most of the current hot spots are clustered in China, where a growing demand for meat products has driven the expansion of large-scale, industrial livestock farming.
Concentrated livestock production is particularly concerning because the practice brings together large populations of genetically similar, often immune-suppressed animals that are highly vulnerable to disease outbreaks, they said.
"Land use changes can have an important impact on human health, both because we are modifying the environment, and also because they can increase our exposure to zoonotic disease," said study co-author Paolo D'Odorico, a professor at the University of California, Berkeley in the US.
"Every formal land use change should be evaluated not only for the environmental and social impacts on resources such as carbon stocks, microclimate and water availability, but also for the potential chain reactions that could impact human health," D'Odorico said.
The researchers also identified locations that could easily become hot spots with changes in land use.
They found that parts of Japan, the north Philippines and China south of Shanghai are at risk of becoming hot spots with further forest fragmentation, while parts of Indochina and Thailand may transition into hot spots with increases in livestock production.
"The analyses aimed to identify the possible emergence of new hot spots in response to an increase in one of three land use attributes, highlighting both the areas that could become suitable for spillover and the type of land use change that could induce hot spot activation," said study co-author Maria Cristina Rulli, a professor at the Politecnico di Milano in Italy.
"We hope these results could be useful for identifying region-specific targeted interventions needed to increase resilience to coronavirus spillovers," Rulli said.
Human encroachment into natural habitat can also can indirectly increase exposure to zoonotic disease by reducing valuable biodiversity, according to the researchers.
When forest lands become fragmented and natural habitats are destroyed, species that require very specific habitat to survive, called "specialists," may dwindle or even go extinct, they said.
The researchers noted that without competition from specialists, "generalist" species, which are less picky about their habitat, can take over.
Horseshoe bats are a generalist species and have often been observed in areas characterised by human disturbance.
Previous work by the research team linked forest fragmentation and habitat destruction in Africa to outbreaks of the Ebola virus.
"By creating conditions that are disadvantageous to specialist species, generalist species are able to thrive," D'Odorico said.
"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, he added.