This article is from the In-Depth Report Ebola: What You Need to Know
Science Talk

David Quammen: The Spillover of Animal Infections to Humans

David Quammen talks about his latest book, Spillover: Animal Infections and the Next Human Pandemic. From his Web site: "The next big and murderous human pandemic, the one that kills us in millions, will be caused by a new disease--new to humans, anyway. The bug that's responsible will be strange, unfamiliar, but it won't come from outer space. Odds are that the killer pathogen--most likely a virus--will spill over into humans from a nonhuman animal"

Podcast Transcription

Steve:       Welcome to the Scientific American podcast, Science Talk, posted on November 18th, 2012. I'm Steve Mirsky. On this episode:

Quammen:         A single spillover that led to the pandemic, led to the pandemic strain of HIV, was from one chimp into one human in the southeastern corner of Cameroon back as far as 1908.

Steve:       That's David Quammen. The New York Times correctly called Quammen "not just among our best science writers but among our best writers, [period]." I and many other Quammen fans first met him through his Natural Acts columns in Outside magazine, which are available in a couple of anthologies. He went on to write the epic Song of [the] Dodo: Island Biogeography in an Age of Extinction. He also wrote Monster of God about the few animals left that are predators of us. His latest book is titled Spillover: Animal Infections and the Next Human Pandemic. He was in New York City recently and we met early in the morning at his hotel near the World Trade Center site, so you might hear some construction sounds in the background. Please forgive my hoarse voice, as I was getting over a respiratory infection of my own. Also, the last few minutes of our conversation featured some profanity because the book does.

Steve:       Your last book was about big animals that kill people and eat them and this to me is almost like a sequel, although there's the extra factor of the diseases moving from the animals into people, but we're really talking about tiny little things that attack people, kill them and eat them.

Quammen:         That's right. And I alluded that at the beginning of this book. I say that predators are big animals that eat their prey from the outside and pathogens are little animals that eat their prey from the inside. So there's a parallel there. And I would say the other parallel is, both in Monster of God and in the Song of the Dodo, I was essentially writing about ecology and evolutionary biology—to some extent about the history of those sciences—with a lot field reporting, a lot of outdoor adventures; and in this book, there's a lot of molecular biology, molecular phylogenetics and things like that in it which took me wonderfully outside my comfort zone, but basically it's a book about the ecology and evolutionary biology of scary viruses.

Steve:       Why is that so interesting to you and probably to most people?

Quammen:         I'd say a couple of reasons. People like horror stories, people like scary things, people like drama, tragedy is compelling, and the world of infectious disease, especially these emerging viral infectious diseases, have all that. They are tragic, they are dramatic, they are horrific, they are scary, they involve human stories. So all that was interesting to me, and [the] science was interesting to me; and then there's the fact that it takes the reader back, and the writer back, to one of those old Darwinian truths—I say this in the book also—that we humans are a kind of animal. So the notion of animal diseases passing into humans is a little bit—what's the word, redundant, tautological? If I'm being really precise, I'd say nonhuman animals spilling their pathogens over in[to] humans. But the basic point is the connectedness between humans and the rest of the natural world, humans and other species; we are inextricably, irrevocably interconnected with other species and one of the ways we are interconnected is by sharing their diseases.

Steve:       You tell a quick anecdote in the book about, I think it was a doctor at a conference who said, "These conditions that you are talking about, Ebola and everything, basically, other than flu and HIV, you know, they're very interesting, [but] they just kill a few people. You know, if you're really interested in stuff that damages millions of lives, why don't you just write about asthma?" [But] you had a really good answer to that.

Quammen:         Well yeah, and I would pass that question along to some of the experts I talk[ed] to. There are a couple of answers. One is that AIDS is a zoonotic disease. So, the ultimate case, the ultimate case in recent history of this phenomenon, is the spillover of HIV in the AIDS pandemic in humans. [You've got] 30 million dead and counting, another 33 million infected. So, you can't say this is just [a] fringe boutique subject. It is true that lots of other more garden variety diseases kill more people each year than most of these emerging diseases have so far. But I asked that question of [a] disease specialist in Bangladesh, in Dhaka, [at] what they call the cholera hospital; he was studying very peculiar disease called Nipah, which spills out of bats and gets into humans and killed 60 percent of the humans or so that it gets into—but that doesn’t amount to huge numbers each year and it amounts to 30 or 40 people each year—I asked him, Steve Luby, "Steve, why study this disease if you've got hundreds of thousands of kids dying of bacterial diarrhea in Bangladesh and cholera?" And he said, "Because this is a really nasty disease, and it could go big, and if it's gonna be studied anywhere, understood anywhere, it has to be understood in Bangladesh because it hasn't emerged anywhere else, except for one time in Malaysia." So he is somebody who cares deeply about the garden variety infectious diseases in the way they affect regular people, especially kids, and yet he says we['ve] got to look at these things because one of these things could really explode.

Steve:       And the more you know before it explodes, the faster you can act if it explodes.

Quammen:         [Absolutely.] If we had got HIV in 1920 and gotten around it, we could have saved millions of lives.

Steve:       You do mention in the later half of the book, [a] lot of people might not know this, that the earliest evidence for HIV in humans is well before the outbreak in the seventies and eighties.

Quammen:         That's right. I don't try to write breaking news, but this is one of the parts of the book that really hasn't been much told, if told at all, for the general public. It comes from [the] scientific literature, papers published in the last four to five years in Nature and Nature Genetics by people like Beatrice Hahn who was at Alabama then, and Michael Worobey at University of Arizona; they have pinpointed to a high degree of persuasiveness, the place and [the] time of the spillover from a chimp into a human of the pandemic strain of HIV. And what they've found, based on molecular phylogenetics and some very good field work and very good lab work, is that the single spillover that led to the pandemic, led to the pandemic strain of HIV was from one chimp into one human in the southeastern corner of Cameroon in central Africa back as far as 1908 or earlier, give or take a margin of error—1908 or earlier. Much different story than we think we know about the origins of AIDS.

Steve:       Let's see the CSI guys do that kind of an analysis. It's quite amazing that they're able to know that's what happened.

Quammen:         It is amazingly precise, but it is as I say, done with very persuasive molecular phylogenetics. They have compared strains of the pandemic strain of HIV around the world, with strains of the simian virus—they called it SIV—that exists as the precursor in chimpanzees; and they've looked at sequences from chimpanzees all over Central Africa, and the close match, [the] really, really close match comes from Southeastern Cameroon. In fact, HIV-1 Group M is the pandemic strain and all of the HIV-1 Group M diversity in humans around the world is a nested subset within the clade of chimpanzee SIV in Southeastern Cameroon.

Steve:       You talk in the book about this, kind of, a feeling of amazement when you realize that the places you had gone to look at Ebola were the same places in which HIV had crossed over into humans.

Quammen:         That's right. I was reading one of these papers in Nature, probably four years ago, a paper by a fellow named Brandon Keele who had been [a] part of Beatrice Hahn's lab and it was about the chimpanzee origins of the pandemic strain of HIV; and they had targeted, they described it in this paper. And there was a map, and I looked at this map, and it showed this little corner of southeastern Cameroon with a little bit of Central African Republic and a little bit of Republic of Congo and a couple of rivers, and I said "I've been there; I slept in that village; I rode in a dugout canoe up that river. Oh my God! That's the origin of AIDS? I got to go there. I got to go back there. I got to retrace that route down that river—the inferentially likely route of the pandemic strain of HIV out of southeastern Cameroon down the Songo River to the Congo River to the big cities, which were then Roseville and Leopoldville, capital of the old Belgian Congo." So I retraced that route in the course of the book research, and that's part of my penultimate chapter.

Steve:       Let's talk about Ebola just for a second. Ebola is pretty well known as this science fiction–like disease because of Preston's book, The Hot Zone, and you, kind of, gently but firmly take Preston to task a little bit in the book.

Quammen:         Yeah, Ebola is the disease that people love to fear. I think of it as the charismatic microfauna in the same sense we have the charismatic megafauna that I wrote about in Monster of God. And Richard Preston made it very, very famous, infamous in The Hot Zone. I do take him to task, I hope gently and politely but firmly, in the book; I don’t want it to be in an argument with him but, and that book was riveting to me when I read it, and it brought a lot.

Steve:       It was to many people; [I remember it vividly].

Quammen:         Yeah, including some of the disease scientists, who read it when they were young and it led them into that field. So it did some very good things. But there are few things that he led people to understand about Ebola that are even more horrific than reality, the notion that people bleed out, as though their bodies were simply being drained off blood—they're bleeding from their eyes, they're melting inside, their internal organs are dissolving. And when I talk to the Ebola experts, people like Carl Johnson and Pierre Rola at the CDC and others, they said, "No, no, it doesn't do that. It is a horrible disease, but it is not horrible in that way." It kills a lot of people, but it's usually, its not necessarily even a particularly bloody disease; they don't call it Ebola hemorrhagic fever anymore, as they did, because they've realized that sometimes it's kind of bloody; it's not as bloody as Crimean-Congo hemorrhagic fever. It is a horrific disease that kills people, but it doesn't cause people to melt down.

Steve:       When you decided that you want to go back into the field, what do you get from that, that [you then] bring to the story; because you're in, everything has happened already, but you're going back into that same environment. So, what experiences do you get that you wouldn't get just from talking to people?

Quammen:         Well I get two things. I like to go into the field with biologists while they're doing their work. I had the opportunity to do that again a fair amount in this book; going into the field, with people like John Epstein in Bangladesh looking for the reservoir host of this virus Nipah, which I mentioned; going into caves in southern China with another scientist who was looking for the reservoir host of the SARS virus. In doing that, I can tell adventure stories, as well as describing scientific data and results, and I like to do that. People like to read about people; even when you write about science, it's advantageous if you tell human stories. So, I'm looking for the stories of these wonderfully gutsy and smart field biologists who study disease ecology, while they're doing their work. And then in some cases, I go without necessarily going with [the scientist]. For instance, I retraced the route of AIDS coming out of southeastern Cameroon. I wasn't with a scientist then, I was just following the track that they had described in their papers. But I learned some interesting things. I talked to local people and local wildlife officials, for instance, about the present-time interactions with chimpanzees, between humans and chimpanzees. I learned about an initiation ritual of the Bakweri pygmy tribe that involves using chimpanzee arms when they initiate young boys to manhood, and it involves having to eat chimpanzee arms. It's sort of an underground practice.

Steve:       It ends unpleasantly as well.

Quammen:         That's risky behavior. That puts you in a risk group, if you're eating chimpanzee arms, and that's going on now. And I saw an AIDS awareness poster in a little office in southeastern Cameroon. It was in French, and it was cartoonishly illustrated. You go to most places in the world, you see an AIDS awareness poster, and it says, "Practice safe sex, use a condom, don't share a needles"; this AIDS awareness poster said, "Beware the red diarrhea, do not eat the apes." Do not eat the apes—that's AIDS awareness.

Steve:       Yeah. That really stood out for me, when I read that too. You know, these people who go out into the field that we don't we hear about are, first of all, incredibly brave and it's really—I haven't seen the movie Contagion, maybe they do cover this, but it's like, these are the real Indiana Jones people.

Quammen:         Oh, I think so. Yeah and, you know, they protect themselves rationally. They wear goggles and respirator masks and rubber boots and tyvek suits in some cases, but you can't protect yourself completely. I talked to one young Congolese doctor, when we were out in the forest, trying to get blood samples from gorillas to look for Ebola antibodies in an area where the gorilla population had been devastated by Ebola—because Ebola affects gorillas and chimps as well as human—and his job is to go out when there is a chimp or gorilla found dead in the forest, and to take tissue samples, to see if it's hot with Ebola. Great, okay, so he dresses up in his tyvek suit, in his hood, in his couple of layers of rubber gloves and he walks up to a chimp that has been rotting for four or five days on the forest floor, and he sticks his scalpel into it to take a tissue sample. Lot of things can go wrong with that. He told me about one time when he did that and it was covered with bees, this chimp carcass, and he reached down to cut a tissue sample, and the bees came running up his arms and he was wearing a vented hood, and they came in under the hood, down across his naked body, and they're stinging him, and he's thinking, "Okay, great, now I've got bees inside my suit that have just been on a chimp carcass that may be hot with Ebola, and they're stinging me." "Why do you do this?" I said to him. He said, "Because I really love my job." Those people are heroes; they're cool.

Steve:       Yeah. That's great stuff. Just to finish up on that ritual, what's it called…

Quammen:         Beka, B-E-K-A, that's the Bakweri ritual, yeah.

Steve:       I said it ends [badly]; it ends with a circumcision.

Quammen:         That's right. (laughs)

Steve:       Let's talk a little bit, I found one of the cases in the book particularly interesting; I don't know why it was [particularly] interesting to me, maybe it's because [of] this knife-edge thing—it's the malaria knowlesi situation.

Quammen:         Malaria knowlesi, right. When I started writing [about] zoonotic disease I did a piece six or seven years ago for National Geographic, so that was when I started really poking into the subject, and I was told, "Well, you can leave malaria off your list, because malaria is not a zoonotic disease, it doesn't pass from [an]  animal host into humans." Yes it's carried by mosquitoes, they're the vectors, but a vector is a different from a reservoir host. And there are no other reservoir hosts for malaria [other] than humans. There are four species of the malarial parasite, four different kinds of plasmodium, including the famous Plasmodium falciparum, and all of those are unique to humans, transferred only from human to human by mosquitoes. Okay, then in the course of researching the book, I came across two wonderful researchers in Borneo, Balbir Singh and his wife Janet-Cox Singh, who have discovered a fifth species of human malaria that was thought to be only a monkey malaria. It's called Plasmodium knowlesi, after a man named Knowles. And this malaria was being misdiagnosed; it was being taken, in humans, it was being taken for a mild malaria Plasmodium malariae, and therefore it wasn't being treated seriously, and consequently people were dying because it is a serious malaria. And then these two folks, the Singhs, recognized that wait a minute, this is this other bug, knowlesi, which is supposed to exist only in long-tailed macaques and pig-tailed macaques; here we’ve got it in humans, so this is zoonotic malaria on the island of Borneo, and to some extent on peninsular Malaysia, that is being carried from monkeys, long-tailed macaques, by mosquitoes into humans. What's the wider significance of that? Well I think about it every time I see that Bill and Melinda Gates, their foundation, which does wonderful work around the world on human health—god bless them—they have the dream of not only eradicating polio but eradicating malaria. If your malaria is zoonotic, you can't eradicate it from humans unless you [either] cure all the animal hosts, cure all those long-tailed macaques in the forest of Borneo, or eradicate them. So, I would love to have [a] conversation with Bill Gates to find out whether he has considered this, [and] whether his scientific advisors have considered this. What do you do, if you're going to eradicate malaria, about zoonotic malaria?

Steve:       Yeah, it's a great question, because you can't just go around wiping out entire species off the face of the earth.

Quammen:         Right, and that's, again, one of the bottom line messages in this subject and of the book: If we're connected to other animals by way of infectious diseases that we share, then as long as we want to live in a world that's rich with biological diversity we need to get used to it. We need to realize that many of these diseases can never be eradicated. They can be controlled. We can protect ourselves against them with vaccines and things, but the whole dream of eradication, in the way that we've eradicated small pox as a human disease and we may eradicate polio, doesn't work with zoonotic diseases. You have to live with them if they abide in other species, and you're not willing to eradicate those other species. A lot of them live in bats; bats already have a big PR problem with humans, but bats are very essential to our ecosystems. So, people hear about this or that disease that comes out of bats; the solution, ladies and gentlemen, please, it is not to demonize bats and eradicate bats, the solution is to deal with the ongoing reality of these diseases.

Steve:       You talk about the benefits of high bio-diversity in one of the conditions because it keeps the number of carriers in check.

Quammen:         Yes, this is something that comes out of work on Lyme disease in suburban New York; work by a fellow named Rick Ostfeld who has been studying the ecology of the Lyme disease system for going on 25 years. One of the things he has found is that the notion, the familiar notion, that well, Lyme disease abides in white-tailed deer, so if you've got a lot of white-tailed deer in your suburban woodland landscape, then that's bad because you're going to have lot of Lyme disease. What Rick Ostfeld has found is, no, it's not dependent on the abundance of white-tailed deer; they're part of the system, but what really matters is the abundance of white-footed mice. White-footed mice are the hosts of the spirochete that causes Lyme disease that give it to the immature ticks, the larval ticks. So, the little ticks, they don't feed on white-tailed deer. [They're] down there close to the ground, they feed on little animals that they can get onto easily. And if you've got a great abundance of white-footed mice, and they [have] a high prevalence of Lyme disease, then a lot of your immature ticks will get infected, they'll bite humans in the course of their lifespan, molting and progressing toward adulthood, and then eventually they will climb on to a white-tailed deer and meet other ticks and mate.

Steve:       That's the singles bar of the tick.

Quammen:         That's the singles bar, yeah. And by the time they get on the white-tailed deer, the chances are that they've already bitten humans, if they're going to do that. And furthermore one white-tailed deer can support thousands of ticks, so you don't need an abundance of white-tailed deer, you just need a few. Therefore the idea of opening your hunting seasons, you want to cut down your deer population and have only a few deer according, to Rick Ostfeld's work it's probably completely ineffectual, completely irrelevant to the human jeopardy of contracting Lyme disease. But if you've got a lot of white-footed mice, your jeopardy is high. Why are you going to have lot of white-footed mice? If you've got a very fragmented ecosystem that has lost a lot of the other small medium size mammals and other animals—if it's lost its squirrels, lost its chipmunks, lost its foxes, lost its possums, lost its owls, lost its hawks. Then your white-footed mice are going to be thriving because they've got no competitors and they've got no predators, so you'll have a lot of white-footed mice, and you'll have a lot of Lyme disease. We love hearing this kind of thing, but it's supported by the data. The message is biological diversity is good for minimizing the risk of Lyme disease.

Steve:       We are in a situation as a species now, where we are really just unwittingly making ourselves just [this] wonderful target for new stuff to attack us, by living in huge concentrated numbers, and by doing damage to the natural habitat so that there are new venues for these diseases to jump from their natural, if you will, hosts to us.

Quammen:         That's right. There're 7 billion of us now on the planet, 7 billion humans, probably heading towards 9 billion in the next 50 or 80 years. There has never been a single species of large body of vertebrate animal on this planet as abundant as we are now. We know that from the paleontological record. It's an unprecedented situation. In ecological terms, it's an outbreak of population. We humans are an outbreak population because we have so exploded in terms of our numbers, in terms of our total mass, in terms of the amount of resources that we irrigate; we're cutting our way through the tropical forests, building timber camps, building villages, killing animals and eating them, disrupting relationships between reservoir hosts and the viruses and other microbes that live within them. I say in the book, "You shake a tree, and things fall out." And that's one of the reasons why there's a drumbeat of increasing cases of these emerging diseases, particularly viruses. We're driving a lot of species towards extinction or simply killing individuals and driving populations down, and we're offering ourselves as alternative hosts. Now viruses don't have intentions. They don't make choices. But given opportunities, they will spill over into new hosts. And when they spill over into humans, they've won the jackpot, they've won the sweepstakes. The way the pandemic strain of HIV won the sweepstakes back there in the early 20th century when it spilled from a chimpanzee, an animal that unfortunately is declining in population, into a human, an animal that's increasing in population; it was a great career move for that virus.

Steve:       For me, and I know for a lot of people who are listening, you've been a presence who we have read for a long time, and there were some little things in the book that I really enjoyed, just because I think the first article of yours the first Outside piece in your Natural Acts career, was about your search for the durian fruit, and then that comes back in the book here.

Quammen:         Yeah, yeah, the durian which is this amazing, difficult fruit, a thing that's about the size of a rugby ball but it looks like a puffer fish with the spikes sticking out all over it. it grows in Southeast Asia on trees, you cut it open with [a] machete and this terrible stink comes out. And there are these big gobbits, like over-stuffed raw oysters of this white, pulpy sweet stuff, and you pick up a handful of this, and you eat it and you get this wonderful vanilla custard—but like no vanilla custard you've ever had—flavor. So, people either detest durian or they love durian, and I happen to love durian. And so in the course of—where was it?—I was in southern China with a scientist named Aleksei Chmura and he's an adventurous eater also, so as soon I hit the ground in southern China, he met me at the airport and we went back to this little apartment with some of his Chinese friends and we piled into durian, he had a couple of fresh durians. So, instead of—this was before dinner—so instead of having peanuts and beer, we were eating durian on a newspaper on the floor of this apartment. It's not for everybody, some people just refuse to eat it; and I guess I have said somewhere, maybe in the book, that it tastes like vanilla custard and it smells like the underwear of somebody you don't want to know. It smells like the gym locker at the end of the summer.


Steve:       I think in your column, which is probably going back maybe 20 years, you might have said something about vanilla custard and sweat socks; you used sweat socks, I don't remember exactly.

Quammen:         Yeah, I think who was it, was it Queen Victoria or somebody among the Victorians, writing about durian early on, back in the age of Alfred Russell Wallace and Charles Darwin, who said that durian was like eating vanilla custard over an open sewer.

Steve:       (laughs) That's pretty good. How many years did you work on this book, six?

Quammen:         I worked on it concertedly for six years, but I got the idea 12 years ago sitting at a camp fire in central Africa and two guys were talking about Ebola; that's a long story and I tell it in the book. They talked about when Ebola struck their village and their friends and loved ones were dying, it was a horrible, horrible event. And one guy mentioned, "You know, it's a peculiar thing, too; when that was happening, we noticed a pile of 13 dead gorillas nearby in the forest." And that phrase just stuck in my mind 12 years ago, and it represented this connectedness that I've talked about; connectedness between us and other species by way of shared diseases, so that's when I started being curious about zoonotic diseases.

Steve:       One of your section titles is "13 Dead Gorillas."

Quammen:         Right, that's the section that's mostly about Ebola; I go from disease to disease but I also, sort of, march through the history of the progression of the ideas—ecological and evolutionary ideas about zoonotic diseases—and that particular chapter is titled "13 Gorillas."

Steve:       And I understand you are back to Africa next month?

Quammen:         You know, [that will] probably be in December, I've been pretty busy with the book, but yeah, I need to get back to work for National Geographic. I am a contract writer, contributing writer for National Geographic. I owe them a couple of pieces; they've been very generous about cutting me a little bit of slack during this book time. I owe them a piece on lions, and so I will be heading back to Africa to spend some more time in the Serengeti and elsewhere.

Steve:       I was just curious about your decision as a writer to use the word "shit" a lot, rather than "feces" or "defecation." You know, you had to do that with intention. Was it just to make it more real to us?

Quammen:         Yeah, when I write even if I am writing about science, explaining science, to the general reader, I try hard to write in a conversational tone. I try to talk to a single reader, a second-person singular pronoun: "you," not "you all." And I try to write to talk in a conversational tone like the tone [that] we're talking in and that I'd [use to] talk to a buddy on the telephone. I don't like high-flown language. I don't like to use, sort of, elevated literary language and I don't like to use euphemism too much. I would like to speak plainly. I admit that when I talk to audiences, including radio audiences, I tend to say "feces" or "excrete" or something, but it's more natural when I am writing the book to call a spade a spade and to call feces, shit.

Steve:       Yeah, there's one sentence that I remember underlining which just talked about, "These people are just constantly working with piss, blood and shit."

Quammen:         Yeah, well those are good Anglo-Saxon words. (laughs)

Steve:       That's it for this episode, read Spillover then read all of Quammen and get your science news at our Web site where you can read Gary Stix's article on "New Revelations about the Unusual Structure of Einstein's Brain," and follow us on Twitter, where you'll get a tweet whenever a new article hits the Web site. Our Twitter name is @sciam. For Scientific American’s Science Talk, I am Steve Mirsky. Thanks for clicking on us.

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