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Understanding Where Coronaviruses Come From And How They Enter Humans


When the COVID-19 pandemic began last year, scientists went looking for the origins of the coronavirus. Right away, they made a huge discovery. It looked like the virus jumped to humans from bats. Now scientists are worried that another animal coronavirus will strike again, so they've gone hunting for other potential sources, and the news is not good. NPR's Michaeleen Doucleff reports.

MICHAELEEN DOUCLEFF, BYLINE: One of the virus hunters is Edward Holmes at The University of Sydney. This past year, he and colleagues trapped several hundred bats in a tiny section of Yunnan province, China, an area about the size of Los Angeles Airport. Then they looked for viruses inside the animals.

EDWARD HOLMES: So in this very small area we sampled, like a thousand hectares, an amazing number of new bat viruses.

DOUCLEFF: In terms of coronaviruses alone, these bats carry 24 new ones, including four closely related to SARS-CoV-2, the virus that causes COVID-19. On top of that, Holmes says these bats are flying all across Southeast Asia.

HOLMES: So you can just imagine if you apply that to the whole of Southeast Asia, what the amazing diversity of these viruses are. And it's just an enormous number of them.

DOUCLEFF: In fact, Holmes says, that if you look all around the world, there are likely thousands of undetected coronaviruses out there, coronaviruses that are different than SARS-CoV-2.

HOLMES: And we're only just starting to scratch the surface of that, and the virusphere of coronavirus is just immense.

DOUCLEFF: And the viruses aren't just in bats. They're in many, many animals - dogs, cats, birds, chickens, pigs, rodents in people's homes.

HOLMES: So under our feet, there is coronaviruses. Above our head in bats, there are coronaviruses. We live almost in a kind of coronavirus world.

DOUCLEFF: And the big question now is how often do these viruses jump from animals into people? Peter Daszak is a disease ecologist at EcoHealth Alliance and an investigator for the World Health Organization. Back in 2003, he and his team tried to answer that question in communities in southern China. They drew blood from about 400 people and looked for signs of previous coronavirus infections.

PETER DASZAK: In one place, we got 2.8% positive, which is pretty high.

DOUCLEFF: That means, at the time, 3 out of every 100 people there had been infected with an unknown coronavirus.

DASZAK: So if you do the math on that and multiply it up, given the total population in Southeast Asia where the bats are that carry these viruses and just the rural population, the ones that are highly exposed, you're looking at over a million people a year getting infected.

DOUCLEFF: In other words, different coronaviruses are constantly jumping from bats and other animals into people. Scientists call this spillover.

DASZAK: It's happening every day. I mean, I look at the spillover event as it's a little bit like rain or snow, you know, with a nice winter snow this year. And it's a bit like snowflakes falling. These viruses are getting into our populations, trickling across.

DOUCLEFF: The vast majority of these spillover events do very little. But each one gives the virus the opportunity to adapt and spread more easily from person to person. And every once in a while, that contagious virus infects a person who finds their way into a city. And so both Daszak and Edward Holmes agree - the next coronavirus outbreak, even the next pandemic, could be right around the corner.

HOLMES: I hate to disturb listeners, but this is not a once-in-100-year event. It could be any time.

DOUCLEFF: It could even be next year.

Michaeleen Doucleff, NPR News.

(SOUNDBITE OF OKAMI (O)'S "UNDERGROWTH") Transcript provided by NPR, Copyright NPR.

Michaeleen Doucleff, PhD, is a correspondent for NPR's Science Desk. For nearly a decade, she has been reporting for the radio and the web for NPR's global health outlet, Goats and Soda. Doucleff focuses on disease outbreaks, cross-cultural parenting, and women and children's health.
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