Hundreds of thousands of people can be infected annually by animals carrying the coronavirus related to the one that causes Covid-19 in China and Southeast Asia, according to a study emphasizing the ongoing pandemic threat of spillover events.
An average of 400,000 of these infections occur each year, most are unrecognized because they cause mild symptoms or no symptoms and are not easily transmitted between people, researchers from the EcoHealth Alliance and the Singapore Duke-NUS School of Medicine said in a study. released Thursday before peer review. and publication. Still, each overflow represents an opportunity for viral adaptation that could lead to a Covid-like outbreak.
The question of where and how the virus that causes Covid emerged has become particularly contentious, with some leaders blaming a hypothetical leak from a laboratory in Wuhan, China that studies pathogens. The new research, supported by the U.S. National Institute of Allergy and Infectious Diseases, is based on evidence that bats are the primary host animals for viruses like SARS-CoV-2 and that people living nearby of their shelters are especially vulnerable.
“This is probably the first attempt to estimate how often people are infected with SARS-related bat coronaviruses,” said Edward Holmes, an evolutionary biologist at the University of Sydney who was not involved in the research. Humans are continually exposed to bat coronaviruses, he said. “Given the right circumstances, one of them could eventually cause a disease outbreak.”
Nearly two dozen species of bats that can be infected by coronavirus inhabit an area of Asia more than six times the size of Texas, and southern China and parts of Myanmar, Laos, Vietnam, and Indonesia are considered the riskiest of the contagion. Peter Daszak and his colleagues at the New York-based EcoHealth Alliance used bat distribution models and ecological and epidemiological data to estimate the risk of exposure to SARS-related coronaviruses and the rate of unreported human-bat infections. in China, South Asia and Southeast Asia.
“If you can stop this at the level of individual infections, you have a much higher chance of stopping the next pandemic,” Daszak said Tuesday in a Zoom interview.
The approach provides a proof of concept for a systematic risk assessment of wildlife overflow events to humans and a strategy to identify key geographic areas that can be prioritized for targeted wildlife, livestock and human surveillance, the researchers said.
Given the challenges of identifying the origins of Covid-19 and the pathways by which SARS-CoV-2 spread to people, this approach may also aid efforts to identify the geographic sites where the flooding first occurred. ”They said in the study.
Almost two years since Covid began infecting people in the central Chinese city of Wuhan, scientists have yet to determine the genesis of the pandemic. Daszak, who supports the wildlife source theory, has been criticized for collaborating in research funded by the National Institutes of Health at the Wuhan Institute of Virology on laboratory studies that some scientists say may have led to the creation of a parent virus.
No evidence has emerged to support the theory of laboratory leaks. Last month, the US intelligence community ruled out the possibility of China developing SARS-CoV-2 as a biological weapon, but no consensus was reached on its origin.
Daszak’s study estimated that a median of 50,000 bat-to-human overflow events occur annually in Southeast Asia and said the number could run into the millions.
That makes the risk of exposure to animal viruses in the wild “much, much greater than any possible exposure in a laboratory,” Holmes said. “And this is just bats. The risk of exposure is even greater when all possible ‘intermediate’ animal species are taken into account ”.
These include minks, civets, raccoon dogs, and other mammals commonly cultivated and traded for food and fur in Asia, according to the research. He said 14 million people were employed in wildlife farming in China alone in 2016, an industry worth $ 77 billion a year.
In Asia, about 478 million people live in an area inhabited by bats carrying the coronavirus, which covers most of Laos, Cambodia, Thailand, Vietnam, Nepal, Bhutan, Peninsular Malaysia, Myanmar, southeast China and the islands. western Indonesia. Hunting, trading, farming and consuming wildlife are common in this region, increasing the risk of exposure to bat-borne viruses, Daszak said.
Wildlife sampling in China has been much more intense than in neighboring countries, many of which are experiencing “dynamic social and environmental changes” known to increase the risk of flood events, Daszak and his colleagues said at the study.
“It’s not about finding viruses and saying ‘this country is high risk for the rest of the world,'” Daszak said. “It’s about finding communities within countries that are at risk and trying to prevent them from becoming infected by helping people in those communities reduce threats to public health.”