Spillover Beasts: Which Animals Pose The Biggest Viral Risk? : Goats and Soda Rodents, primates and bats likely carry hundreds of thousands of viruses we haven't yet identified. But how do you know which ones might infect humans?
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Spillover Beasts: Which Animals Pose The Biggest Viral Risk?

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Spillover Beasts: Which Animals Pose The Biggest Viral Risk?

Spillover Beasts: Which Animals Pose The Biggest Viral Risk?

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KELLY MCEVERS, HOST:

This next story is about where certain viruses are hiding around the world. Scientists have some new information about that and about how many might be out there. NPR's Michaeleen Doucleff says the number is surprising.

MICHAELEEN DOUCLEFF, BYLINE: Here's a question for you. Where do new human viruses come from like Ebola and Zika? Kevin Olival at EcoHealth Alliance says the answer is surprisingly simple.

KEVIN OLIVAL: Most of these come from wild mammals.

DOUCLEFF: Wild mammals - that includes exotic creatures like chimpanzees in Cameroon but also just your run-of-the-mill rodents in the Midwest. Olival and his colleagues studied the ecology of diseases, and for the past decade, they have been trying to figure out how many viruses are hiding in animals worldwide. They've scoured studies and analyzed databases and then added them all up.

OLIVAL: We're talking about almost 600 viruses. So 586 unique viruses are in the dataset and about under 800 mammal species roughly.

DOUCLEFF: Six-hundred viruses sounds like a lot, but here's the thing. That's just the viruses that we know about. Olival and his team then took their analysis one step further.

OLIVAL: We predict how many more viruses are out there on the planet and where should we go to look for those.

DOUCLEFF: So what's the answer? How many more viruses are out there?

OLIVAL: We expect there's hundreds of thousands of viruses out there, things that...

DOUCLEFF: Wait. Wait. Wait. Wait. Wait. A hundred thousand viruses are out there.

OLIVAL: Yeah, very likely.

DOUCLEFF: Olival and his team published the results in the journal Nature. They estimate that most of these viruses are in the tropics. For instance, bat viruses are concentrated in the Amazon, and monkey viruses are primarily in Central Africa and Southeast Asia. But the U.S. isn't exempt.

OLIVAL: For rodent viruses, there's actually some sort of hotspots within the U.S.

DOUCLEFF: Specifically, the researchers predict there's a bunch of rodent viruses on the western side of the Rocky Mountains. And this finding actually matches up with results from another study which found a hotspot for rodent viruses in the Midwest in Nebraska and Kansas.

OK, before you hop up and buy a bunch of hand sanitizer or get angry at that squirrel outside your window, Barbara Han, a disease ecologist at the Cary Institute, says there's really no reason to be alarmed.

BARBARA HAN: I mean I wouldn't go snuggle up with a rodent (laughter), but I wouldn't be afraid.

DOUCLEFF: Because, she says, these viruses have likely been hanging out in Midwestern mice and voles for many, many years, causing no problems at all. How many of these viruses do we really need to worry about?

HAN: So that is the golden question, right? I mean we want to know not just how many were missing and we don't know about, but we want to know the ones that are going to be a problem, the ones that are posing the risk to humans.

DOUCLEFF: To do that, we have to do more than just map out where viruses are. We have to actually figure out what makes that Ebola virus decide one day it's going to jump from a gorilla into a person. Michaeleen Doucleff, NPR News.

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