Thousands of COVID-Like Cases With Animal Source Raise Risk of Future Pandemics

New Delhi: An study emphasising the ongoing pandemic threat from spillover events has established that hundreds of thousands of people may be infected annually by animals carrying coronaviruses related to the one that causes COVID-19 in China and Southeast Asia.

Most of the average 400,000 such infections that occur each year go unrecognised because they cause mild or no symptoms and aren’t easily transmitted between people, researchers with the EcoHealth Alliance and Singapore’s Duke-NUS Medical School said in a study released on Thursday before peer review and publication. Still, each spillover represents an opportunity for viral adaptation that could lead to a Covid-like outbreak, Bloomberg reported.

Bats are the main host animals

The new research, supported by the U.S. National Institute of Allergy and Infectious Diseases, builds on evidence that bats are the main host animals for viruses like SARS-CoV-2 and that people living near their roosts are especially vulnerable.

“This is probably the first attempt to estimate how often people are infected with SARS-related coronaviruses from bats,” Edward Holmes, an evolutionary biologist at the University of Sydney who wasn’t involved in the research was quoted as saying, adding that humans are continually exposed to bat coronaviruses. “Given the right set of circumstances, one of these could eventually lead to a disease outbreak,” he said.

Almost two dozen bat species that can be infected by coronaviruses dwell in an area of Asia more than six times the size of Texas, with southern China and parts of Myanmar, Laos, Vietnam and Indonesia deemed the riskiest for spillovers, Bloomberg reported.

Peter Daszak and colleagues at the New York-based EcoHealth Alliance used bat distribution modelling and ecological and epidemiological data to estimate the risk of exposure to SARS-related coronaviruses, and the rate of unreported bat-to-human infections in China, South Asia and Southeast Asia.

“If you can stop this at the level of individual infections, you’ve got a much higher chance of stopping the next pandemic,” Daszak said Tuesday in a Zoom interview.

Daszak supports the theory of wildlife source. His study estimated a median of 50,000 bat-to-human spillover events occur in Southeast Asia annually and said the number could run into the millions.

Then there are ‘intermediate’ animal species.” These include mink, civets, raccoon dogs, and other mammals commonly farmed and traded for food and fur in Asia, according to the research. It said 14 million people were employed in wildlife farming in China alone in 2016 — an industry worth $77 billion annually.

In Asia, about 478 million people live in an area inhabited by coronavirus-carrying bats, covering most of Laos, Cambodia, Thailand, Vietnam, Nepal, Bhutan, peninsular Malaysia, Myanmar, southeast China, and the western islands of Indonesia. Wildlife hunting, trading, farming and consumption is common across this region, increasing the risk of exposure to bat-borne viruses, Daszak said.

Wildlife sampling in China has been far more intense than in nearby countries, many of which are undergoing “dynamic social and environmental changes” known to increase the risk of spillover events, Daszak and colleagues said in the study, Bloomberg reported.

“This isn’t about finding viruses and saying ‘this country is a high risk to the rest of the world,’” Daszak was quoted as saying. “This is about finding communities within countries that are at risk and trying to block them from getting infected, helping people in those communities reduce public health threats.”