Researchers of the EcoHealth Alliance and Singapore’s Duke-NUS Medical School have raised an alarm over the possibility of a new pandemic from spillover events.
The study, released on Thursday before peer review and publication, estimated 400,000 such infections happen every year. Most of them, however, go undetected because they either have mild or no symptoms and are not easily transmitted between people.
It said that each spillover event – when a virus overcomes naturally occurring barriers to “spill over” from one species to another – could lead to a Covid-like outbreak.
The origin of the novel coronavirus, which causes Covid, remains a mystery and has become a matter of contention among world leaders and experts alike, years after the disease emerged and spread to become a pandemic.
At the heart of the controversy are two theories that suggest the deadly virus either naturally “spilled over” to human beings from bats through an intermediary host animal or that the virus spread as the result of a lab leak.
The research by New York-based EcoHealth Alliance and Singapore medical college builds on the former theory that suggests bats are the main host-animals for viruses and people living in the vicinity of the mammals are most vulnerable.
The research was supported by the US National Institute of Allergy and Infectious Diseases.
“This is probably the first attempt to estimate how often people are infected with Sars-related coronaviruses from bats,” Edward Holmes, a biologist at the University of Sydney who was not involved in the research, told Bloomberg.
He said it was not unusual for humans to be exposed to bat coronaviruses. “Given the right set of circumstances, one of these could eventually lead to a disease outbreak,” he added.
The Asian subcontinent is home to almost two dozens bat species that can be infected by coronaviruses. Southern China and parts of Myanmar, Laos, Vietnam and Indonesia have been found to be most vulnerable for spillovers, according to the study.
Mr Holmes said: “This is just bats. The risk of exposure is even higher when you factor in all the possible intermediate animal species.”
The study found that in Asia alone, there are about 478 million people, who live in areas inhabited by coronavirus-carrying bats.
Peter Daszak and his colleagues at the New York-based EcoHealth Alliance estimated that about 50,000 bat-to-human spillover events occur in South-east Asia annually and the conservative figure could actually run into millions.
Dr Daszak has faced criticism from several quarters for collaborating in research funded by the National Institutes of Health at the Wuhan Institute of Virology, which has been at the centre of the lab-leak theory.
The theory, which was earlier dismissed as a far-right conspiracy theory, has since seemingly been acknowledged by many in the scientific community.