SOREN WHEELER: Hey, this is Soren Wheeler, senior editor and producer at Radiolab with a quick update. So David Quammen's book Spillover has—it's been out for a couple years now. And as we all know, we are actually now at this moment facing the tragic consequences of another spillover. This time it's the Ebola virus, and we found ourselves wondering just how far it's going to spill.

SOREN: Okay? All right. Okay.

SOREN: So Robert and I called up David Quammen again. He had actually just reprinted with updates the chapter about Ebola from his book.

DAVID QUAMMEN: Yeah. Ebola: The Natural and Human History of a Deadly Virus.

ROBERT: First of all, how old is this disease? Anyone have any idea?

DAVID QUAMMEN: Well, as a human disease, as far as we know it dates to 1976. There was this outbreak of a strange disease at the Yambuku Mission in northern Zaire.

SOREN: 318 cases. 280 people die.

DAVID QUAMMEN: And then there was another one in Sudan at about the same time.

SOREN: This time 151 people die, and then it just disappears.

DAVID QUAMMEN: Hiding in the forest.

SOREN: Without a trace. Until in 1994, thousands of miles away in Gabon another outbreak.

DAVID QUAMMEN: Yes. That's—that's the history since 1976. It disappears for—for two or three years at a time. Sometimes it disappears for a decade, and then it spills over and causes a human outbreak.

ROBERT: Well, if—if something is in the closet and is going to jump out at you, then the natural question to ask is where's the closet? Like, where is it hiding?

DAVID QUAMMEN: Well, the main suspects are bats. We don't know that for sure, because nobody has ever isolated live Ebola virus from an African bat.

ROBERT: Have they tried? Have they looked in lots and lots of bats?

DAVID QUAMMEN: Yeah, they've looked in lots—they've looked in all kinds of animals. They've looked in insects. They've looked in snakes. They've looked in forest antelopes. They've looked in monkeys. They looked in plants. Literally hundreds of different species they looked in. Found zero traces of live Ebola virus.

SOREN: So we really don't know where it's coming from or where it might come from next.

DAVID QUAMMEN: No. No.

ROBERT: Can I just ask you just to describe the Ebola virus? It's—it's apparently—viruses are generally teeny. Is this a teeny, teeny, teeny one?

DAVID QUAMMEN: Yes. Yeah. It's a teeny virus. It belongs to a family they call the filoviruses. Filo as in thread. It's a—it's a spaghetti-shaped virus. Its genome is carried on just one strand of the—the genetic material RNA.

SOREN: And while those genes have let the virus live happily for hundreds of thousands, even millions of years in bats or whatever animal it lives in, when it gets into humans ...

DAVID QUAMMEN: Ebola burns too hot.

SOREN: ... it makes so many copies of itself so quickly that it just destroys the body and the person is usually dead within a few weeks, which David says is actually bad for the virus, because Ebola can only pass through direct contact with bodily fluids and because it kills so quickly, it doesn't have a lot of opportunities to get into the next person.

DAVID QUAMMEN: So the scientists have a term for that, too. They call—at least they used to call us a 'dead-end host.' How's that for a phrase? We're the dead-end host of Ebola. And that means that when Ebola gets into us, it has no great future. It's either gonna burn out and come to an end or we're gonna stop it. But right now, we don't seem like a dead-end host.

SOREN: Yeah. I am wondering, like, you know, if we've—if, since we've started noticing in 1976 a burst here, a burst there, why—why now this? Why is it ...

DAVID QUAMMEN: Yeah. That's the big question for Ebola, 2014. This time we've got a very different situation. It's gotten out of control. Why has it gotten out of control? Well, partly because we recognized it late. It began back in December of 2013 with a two-year-old boy in southeastern Guinea. At least he's the first known case at this point. He died. His mother died about a week later. His sister died, his grandmother died, other people in the village died. This went on from early December until the middle of March.

SOREN: By then it had spread from these small villages into larger cities in part, David says, because well, previous outbreaks had been in very remote places, it now found itself in a more densely-populated area.

DAVID QUAMMEN: The capital cities in these small West African countries are not very many miles away from the villages of the countryside. Then the virus got into these poor neighborhoods like West Point, where people were living together in—in crowded, slum-like neighborhoods. And—and when their loved ones got sick, the people took care of them. And when their loved ones died, people cleaned the bodies and—and touched the bodies and said goodbye to them. So the infection spread. And of course, those—those dense, poor neighborhoods in the capital cities are not that far from the international airports. So suddenly you've got the opportunity for the—almost the first time, for Ebola to get on an airplane.

SOREN: So if you—have people changed the way they think about Ebola, because I mean, is there a mood shift there?

DAVID QUAMMEN: There's a little bit of a mood shift, but the experts, the scientists, the public health officials are still saying this is not that kind of virus. It still is, as far as we know, a virus that is only transmissible by direct contact with bodily fluids. It should be easy to stop, easy to contain.

SOREN: But according to David, the thing that some scientists are worried about is that as Ebola gets into more and more people and makes more and more copies of itself, it's changing.

DAVID QUAMMEN: Yes, every time it replicates there is a chance of a mistake.

SOREN: There's a chance that the genes for the next virus will come out just a little bit different. It'll mutate.

DAVID QUAMMEN: Most mutations are either insignificant or they do damage. But occasionally, there can be a mutation that might possibly help the virus.

ROBERT: Can we track these things? Like, can we—can we take a person who's got sick of Ebola in Sudan and compare it to a person who's sick of Ebola in the Congo, and compare that to a person who's sick of Ebola in Niger or in wherever. Can we do that and see whether it's changing?

DAVID QUAMMEN: Yes. And it has been done. Steven Guyer and his colleagues published a paper in Science in early September which involved doing exactly that.

SOREN: And one of the things they found, says David, is that since this virus has been in us during this outbreak, it's been changing twice as fast as it has previously when it's living in it's animal hiding place.

DAVID QUAMMEN: Yeah. So it has had more opportunities to replicate in more different people. It hasn't just been in 300 people. It's been in 9,000 people now.

ROBERT: That—is that the key word? Is that the more opportunities you have to have a 'good mutation,' from your point of view, that this is suddenly—this disease has gotten an enormous number of opportunities?

DAVID QUAMMEN: That is the operative word, yeah. Mm-hmm.

SOREN: Are there boundaries around that? I mean, like, do we have any sense of how big a leap it would be for this to suddenly be transmissible in the air?

DAVID QUAMMEN: Yeah. We know that for this to spread through the air, there are very special machinery, you know, grappling hooks, proteins on the outside of a virus that help it catch hold of particular cells and enter them. And Ebola doesn't have the right grappling hooks to lay hold of cells in the respiratory tract and get in them and then come bursting out of them and be carried outward on your breath. To get to that point would require a number of mutations, each of which is infinitesimally unlikely. And when you ...

ROBERT: Is that a mutation that it would be startling, like a what to a what?

DAVID QUAMMEN: Yeah, some people have been saying that it would be like mutations that allowed a giraffe to fly. But there are other scenarios that are a little more probable. For instance, it might mutate and adapt in such a way that it kills fewer people or kills them more slowly, and leaves people infectious for a longer period of time. Maybe people are walking around for three or four weeks with an occasional vomiting episode, but they're not dying. That would potentially give Ebola a greater opportunity to spread among more people.

SOREN: What—this is not a fair question to ask you, but what should we be doing?

DAVID QUAMMEN: I think the most important thing we should be doing is not letting the public health versus civil liberties issues in the US distract us from West Africa. As the case count gets—we've talked about this. As the case count gets higher, it has more opportunities to mutate and therefore more opportunities to adapt. So we need to end this outbreak in West Africa before this virus learns too much about us.

SOREN: Thanks again to David Quammen. His book is Ebola: The Natural and Human History of a Deadly Virus. We'll be back in just a moment.

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