When Infections "Spillover"

In his new book Spillover writer David Quammen traces the evolution of Ebola, HIV and other diseases that moved from animals to humans. Quammen describes how scientists look for the reservoirs of the infectious agents, and what might be done to prevent the next pandemic.

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FLORA LICHTMAN, HOST:

Up next, planning for the next pandemic, or at least trying to. If you've seen the movie "Contagion" or read "The Hot Zone," you've gotten a taste of what happens when an infection jumps from animals to people. These spillovers, as they're called, can be deadly, but they're not always fast-moving or bloody, and scientists don't always figure out what happened or come up with a cure.

In his new book, my next guest explores the natural history of some of the scariest animal-to-human diseases - Ebola, HIV and some lesser-known ones, too - to see if we can learn about them and maybe, I don't know, stop the next pandemic from happening.

David Quammen is author of "Spillover: Animal Infections and the Next Human Pandemic." He joins us from WGBH in Boston. Thanks for joining us.

DAVID QUAMMEN: Nice to be with you, Flora.

LICHTMAN: This is a little bit of a scary book.

(LAUGHTER)

QUAMMEN: It is. It's a book about scary new emerging diseases and where they emerge from, and where they emerge from generally is wildlife. There are a lot of gruesome stories and suffering and disease and even death in the book, although I hope it's uplifting and empowering in certain ways, too, even a page-turner because there are some very heroic scientists and state-of-the-art scientific and public health work that's being done around this subject.

LICHTMAN: Well, it's amazing how many places you go to, and we're going to talk lots more about "Spillover" when we come back from this break with David Quammen, but you really traveled all over the world.

QUAMMEN: Well, I've been chasing the subject for six years, and it did take me around the world, from eastern Australia to Bangladesh and Malaysia and Borneo and the Congo and a lot of other places.

LICHTMAN: Stay tuned for more animal diseases. If you're a disease enthusiast, interested in viruses, you should definitely stay tuned, fascinating stories to come.

QUAMMEN: If you're a health enthusiast, too.

LICHTMAN: Yeah, that's true, you're right, let's make that clear, too. We'll be back after this break.

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LICHTMAN: This is SCIENCE FRIDAY from NPR.

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LICHTMAN: This is SCIENCE FRIDAY, and I'm Flora Lichtman. We're talking this hour about infections that spread from animals to humans. My guest is David Quammen. His new book is "Spillover: Animal Infections and the Next Human Pandemic."

Walk us through a textbook case of a spillover.

QUAMMEN: OK, there's the one that I begin the book with. It's a virus called Hendra, H-E-N-D-R-A. It's a very small, sort of boutique disease, but it is a textbook case. In 1994, horses suddenly started getting very sick at a stables in eastern Australia, in the suburb of Brisbane called Hendra.

Their faces swelled up. Their breathing became labored. They became clumsy, stumbling, falling down, and bloody froth started coming up their throats, up their windpipes, out their nostrils and mouths. Three men tried to take care of them: a veterinarian, the trainer of the stables and a stable hand.

They were reaching down the throats of the horses, trying to clear their windpipes and things. The horses started to die. One by one they went down. Something like seven horses died in 12 hours and more after that. And then the men started getting sick.

The horse trainer got sick with what seemed like a bad flu, went into the hospital. The stable hand got sick and went home, and then the horse trainer died. The stable hand slowly got better. They isolated a virus from the dead horse trainer, and it was a virus they'd never seen before. They looked in the horses. They found the same virus. They gave it the name Hendra, and then they started on the detection work trying to figure out where this virus had come from and how it had spilled over into the horses.

And eventually they found that the virus abided in giant fruit bats, a couple different species of giant fruit bat that were native to that part of Australia. The fruit bats had been roosting in trees, fig trees, eating figs and dropping pulp, dropping their feces and urine onto the grass beneath, and one of the horses had been staying in a pasture out there by those fig trees, had gone into the shade under the tree, had eaten the grass, picked up the virus, and then when she was brought back to the stable with the rest of her fellow horses, she passed the disease on to them, and they passed it on to the humans.

So it was spillover from a bat into horses. The horses became sort of amplifier hosts of the virus, and it spilled onward from them into humans. The mortality rate of that disease is around 50 percent.

LICHTMAN: And where is it now? I mean, has it popped up again since you wrote about it?

QUAMMEN: It has popped up, but like some of these diseases, it pops up, and there's an outbreak, a local outbreak, and the case of Hendra usually infects no more than one or two humans, might kill one out of two. In some of the other cases, like Ebola virus in Central Africa, it might kill a dozen or a few dozen people. There's been an outbreak going on in the Democratic Republic of the Congo this summer.

And then these diseases disappear. They might disappear for years at a time. Then again there's another outbreak. When they're gone, when they're missing, they're living secretly, inconspicuously, harmlessly in some sort of an animal, some sort of an animal species. The scientists call that the reservoir host.

And then occasionally because of some kind of accident or disruption or circumstance, they - the viruses or the other pathogens spill over from reservoir host, get into humans or other animals and cause outbreaks of disease.

LICHTMAN: They're hiding out. That's - that part I really was fascinated by.

QUAMMEN: Yeah, and that sounds a little anthropomorphic. I mean, they live in those reservoir hosts inconspicuously. Obviously viruses don't have purposes, so it's not their purpose to hide, but they disappear. They go somewhere where we can't find them.

Scientists - Ebola spilled over for the first time in 1976, and scientists still don't know what the reservoir host of Ebola is.

LICHTMAN: If you want to get in on the conversation, ask David Quammen a question, it's 1-800-989-8255, 1-800-989-TALK. Now these are called zoonosis, is that - did I get that right?

QUAMMEN: That's right, yeah, zoonoses. A zoonosis is an animal infection that's transmissible to humans. It might or might not cause disease in humans. Sometimes these things spill over, and they become innocent passenger viruses in humans. But if the zoonosis spills over and does cause disease, then we call that a zoonotic disease. And about 60 percent of our infectious diseases are zoonotic.

LICHTMAN: What makes one virus able, for example, to spill over and another not able to do that?

QUAMMEN: Well, one of the things that determines that is just circumstance, opportunity. When we humans go into the tropical forests and cut down trees and alter the ecosystems, disrupt things, come in contact with lots of different kinds of animals, all of whom are carrying viruses of their own, then we present opportunities for those viruses to be passed from these animals into us.

If we kill the animals and butcher them and eat them, those are opportunities for viruses to enter a new host. Some viruses might get into humans, and humans are dead-end hosts. They might kill a number of humans, but they don't transmit from human to human very well.

And then in other cases, the viruses discover that not only is this good habitat for them, this human they've spilled into, they can replicate, they can cause mayhem in that human, but they find they can also pass along to other humans.

Maybe they pass along in bodily fluids. Maybe they pass along through the air, on a cough or a sneeze. And those are the ones that become not just outbreaks but epidemics and pandemics.

LICHTMAN: And some humans are even call super-spreaders. Can you - do we know why some people are super-spreaders?

QUAMMEN: Well, we don't know why, but we know that it happens, this phenomenon of super-spreaders. It's a little bit similar to the famous case of Typhoid Mary, but a super-spreader is a person who becomes infected with one of these diseases, and then Typhoid Mary didn't show symptoms, but these super-spreaders generally show severe symptoms, and they pass their infection along to more than their share of secondary cases of other people.

For instance when SARS, SARS virus spilled over into humans in Southern China and then got to Hong Kong in 2003, it was amplified out of Hong Kong and went on to Toronto and Hanoi and Beijing and Singapore. But one of the reasons it was amplified is because there were a couple of super-spreaders in the case of SARS, two men who were very sick and who really spewed the virus out and infected a lot of health care workers.

In one case, a man was staying in the hotel, in the ninth floor, and he infected people up and down the corridor of that hotel. Then they got up the next morning and got on airplanes and went home to these cities around the world carrying the SARS virus with them.

LICHTMAN: Is this one of the examples where they call him the poison king? Is this - am I thinking of the right one?

QUAMMEN: That's right, one of these men - yeah, there was a seafood, wholesale seafood dealer in Southern China, in the province of Guangdong, who got the nickname the poison king because he had infected so many other people. He got very sick, went into a hospital in the city of Guangzhou. He started to suffer respiratory blockage.

They intubated him, they put a tube down his throat to help him breathe, but in the course of doing that, he was - you know, he was spewing out virus, he was coughing and sputtering and spitting. And health care workers became infected just in the course of intubating him.

So he infected more than his share, and then there was the other fellow at the hotel who infected more than his share.

LICHTMAN: It really - your book really made me feel a huge debt of gratitude to people who work in the health care industry because it can be really heroic work, and it seems like they put their life on the line in some cases.

QUAMMEN: Oh absolutely yeah. Some of the people I spent time with, I document, I describe, I tell stories of their field work. I went with some of them to places like a rooftop in Bangladesh in the middle of the night, the roof of a warehouse where a wonderful scientist named Jon Epstein who works for EcoHealth Alliance, was trapping, again, giant fruit bats to look for a disease, a virus called Nipah.

Now this is not the same NEPA that your previous guest referred to, not the National Environmental Policy Act. This is N-I-P-A-H, named after a village in peninsular Malaysia where this virus was first identified. So Jon Epstein is on the roof of a warehouse in Bangladesh in the middle of the night wearing goggles and welder's gloves and a respirator mask, handling these giant fruit bats that he's catching in a mist net, taking them into a provisional lab, drawing blood samples from them, knowing that the virus is probably there somewhere and that it's a very lethal virus.

It's as lethal as Ebola. He's putting it in, putting - taking blood samples and putting them into little tubes that'll go back to a lab in the U.S. with help from some very gutsy and proficient Bangladeshi collaborators. It's tough work, it's dramatic work, it's scary work, but they love it.

LICHTMAN: And you too. I mean, you know, some of - literally a paragraph began: Before I knew it, I was helping trap monkeys in a shrine in Bangladesh. And I think...

(LAUGHTER)

QUAMMEN: That was with another wonderful researcher named Lisa Jones-Engel and her physician husband, Gregory Engel. They were looking for viruses in monkeys, yes, in macaques, long-tailed macaques and other macaques that, in some parts of Southeast Asia, become habituated as temple monkeys.

And this was a temple in northeastern Bangladesh where I was helping them trap these monkeys so that, again, they could tranquilize them, take blood samples, looking for a virus called simian foamy virus. How's that for a name? That's one of my favorites. Simian foamy virus. And - which is a marker, which is, so far, as we know, a harmless virus when it passes into humans.

But it's sort of an indicator for the fact that there are opportunities for viruses to pass between monkeys and the humans that visit these temples. And there are much more serious, dangerous viruses, including one called herpes B, that could also pass into humans and cause terrible symptoms and death.

LICHTMAN: Did you worry about your own life on this reporting trips?

QUAMMEN: I didn't worry about it too much, but I - you know, I love life. I love to be out there in the field with these scientists. I take the same precautions they take. If they're wearing respirator masks and goggles and latex gloves, then I wear the same - rubber boots, gowns or whatever. And I try and stay three feet or 4four feet behind them. I try not to let them hand me a giant fruit bat.

In one case, Lisa Jones-Engel did say, here, David. Pin this monkey to the ground while I take a blood sample from this other one. And I thought about that a little bit.

LICHTMAN: Did you think twice?

(LAUGHTER)

QUAMMEN: I said - well, I didn't think - well, I said, sure, and I held it to the ground. And then I thought, this is not exactly what I signed up for, but, you know, you need to pitch in a little bit in these circumstances.

LICHTMAN: For a disease, a virus to spill over, is it just a matter of coming in contact with the right animal? Is it just chance, or does there have to be something special about the virus itself to be able to infect multiple species?

QUAMMEN: Well, some kinds of virus, yes, are better at this than others. And the scientists who watch the world for the next spillover are particularly vigilant about single-stranded RNA viruses, as distinct from DNA viruses that carry their genomes on the good old, stable double helix. RNA viruses, when they replicate, mutate more frequently. Therefore, there's more change. There's more genetic variation in the populations of those viruses. They replicate very abundantly, so their populations are large.

And those two factors - genetic variation and large populations - are perfect recipes for Darwinian evolution. So RNA viruses evolve very quickly. They adapt very quickly. If they pass from one species of host into another - for instance, from a bat, or a monkey or a rodent, into humans - they seem to have a better chance of flourishing, of adapting to the new host and finding ways to transmit onward. So the RNA viruses, the single-stranded RNA viruses, are particularly on the watch list for the disease scientists who study this field.

LICHTMAN: I'm Flora Lichtman, and this is SCIENCE FRIDAY from NPR, talking with David Quammen about his book "Spillover." Are we reservoir hosts for viruses that have caused pandemics in other animals?

QUAMMEN: Well, certainly we've caused disease. It does go the other way. It can go either direction whenever there's fairly close contact. For instance, Jane Goodall's chimps in Gombe in Tanzania, in the late '60s, suffered what seems to have been a little epidemic of polio. A number of the Gombe chimps died.

And that polio virus is thought to be non-zoonotic. It's thought to be a virus that only affects humans, but it's capable of passing from humans into chimps. So it seems to have made those chimps sick and killed some of them.

Likewise, the mountain gorillas of Rwanda and Uganda, when people visit those on - ecotourist adventures, they're not allowed to come closer than within about 15 feet. The gorillas are habituated. They're perfectly happy to have people nearby.

But the people who manage those gorilla populations are concerned that diseases, human diseases, will spill over into the mountain gorillas, which are an endangered subspecies and have a relatively small gene pool. So, yes, we have to be careful that we don't give diseases to wildlife also, especially wildlife that's closely related to us and that's endangered.

LICHTMAN: It seemed like many of the viruses you talk about in this book spilled over from bats, and I don't think of them as close relations to us particularly. But do we have...

QUAMMEN: No, no.

LICHTMAN: ...some kind of kinship with their immune system or something?

QUAMMEN: Well, bats are mammals, so they're closely related. They're more closely related, obviously, than birds or reptiles. But you're right. There is a pattern. More of these viruses, these newly emerging viruses, have come out of bats, spilled over from bats, than one might expect. And this raises a question among the researchers, why bats? Are they disproportionately represented as the reservoir hosts of these viruses that spill over?

One answer, one possible answer is, no, they're not because bats - they only seem to be disproportionately represented because bats represent 25 percent of all mammal species. They're really, really diverse order of mammals, so that if they seem to be overly represented, it may just be that there are so many different kinds of bats.

But the other possibility is that there are differences. Bats live in huge colonies, huge aggregations, hundreds of thousands or millions of individuals packed closely together. They have long life spans. They live 18, 20, 25 years, unusual for a small mammal. And those factors plus a couple of other things related to their immune systems may make them much more hospitable habitat or ecosystems for viruses. So there may be more viruses waiting to spillover in bats than in other creatures and that might account for this seeming disproportion.

LICHTMAN: I have really 30 seconds - 20 seconds left. But tell us, just quickly, if there's anything we can do to help protect ourselves.

QUAMMEN: Well, get your flu shots, pick the ticks off our child when she comes in from playing in Lyme disease territory, get a good insect repellant if you're living in North Dallas so that you don't get bit by a mosquito carrying West Nile fever. But more importantly, learn about this, support the researchers and understand the science underlying these zoonotic diseases.

LICHTMAN: That's a perfect place to leave it. Thank you for joining us today, David Quammen.

QUAMMEN: My pleasure, Flora. Nice to talk with you.

LICHTMAN: David Quammen is the author of "Spillover: Animal Infections and the Next Human Pandemic. And this is a terrific place to learn about viruses, disease and exactly what David Quammen said. When we come back, we'll talk about the brains behind an online campaign that raised over a million dollars for a museum to honor Nikola Tesla. You may know him from The Oatmeal. Stay tuned. This is SCIENCE FRIDAY from NPR.

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