Back in 2003, a new virus that would be called SARS jumped from a bat to a civet cat to human beings, eventually infecting thousands and killing nearly 800 people. That’s just one example of the threat that animal microbes can pose to human beings, and it’s a story that the veteran science journalist David Quammen tells in his new book Spillover: Animal Infections and the Next Human Pandemic. Quammen spoke with TIME’s Bryan Walsh about the origin of Ebola, the threat of sick animals and some particularly troublesome bees.
TIME: Why are we so transfixed by the threat of these new infectious diseases, what you called the next big one?
Quammen: Well, we know that previous big ones have been very big. The 1918-19 influenza killed 50 million people. AIDS has killed 30 million and counting. And scientists know that another of these things is very likely to come along that has the same sort of potential. There are so many humans on the planet now — 7 billion of us — and we live so completely interconnected with one another, and we’re pressing, ever and more insistently into the wild places where these undiscovered viruses live, that it seems highly likely, if not inevitable that something else, something new, is going to spill over into the human population. It will have two characteristics. One, it’ll be very virulent, capable of killing people. Two, it’ll be very transmissible, capable of leaping quickly from one person to another. And if that happens, we’ve got big trouble.
Is this threat worsening? Obviously there are more human beings on the planet, and we’re obviously pushing into wildlife habitats, even as we connect the planet more than ever before. Does that raise the risk?
It does, and there seems to be an increasing drumbeat of these diseases. In the book I recite a whole list of them, beginning with Machupo in the early 1960s, and Ebola, and Marburg, and Hanta virus, and SARS, and nipah, and hendra. So it does seem to be getting worse, for exactly the reasons that you touched on. We are pressing more and more insistently into those wild places. We’re eating bush meat—we’re eating primates and rodents. People in the tropical forest are hungry for proteins, so it’s only normal, it’s inevitable that’s going to be happening more and more insistently, in greater volume. And we exist in greater volume, so that if there’s a virus that lives in a chimpanzee or a monkey and that animal is becoming endangered, then the virus has two options. It can go extinct with its host species, or it can make a leap into a new host. And if it makes the leap into humans and is able to transmit, then it’s hit the jackpot.
We’ve had a few close calls with new diseases like SARS, which I witnessed as a reporter in Hong Kong in 2003. Are we getting lucky, or are we actually heading these diseases off?
We are helping — we are doing some good work. It’s interesting that you were there, close up, to see SARS, because the scientists in this field that I talk to, when you ask them, what’s the one that scares you the most that we’ve seen already, SARS is the one that had the greatest potential to be much, much worse. That was the bullet that flew by our ear. And it wasn’t just that we were lucky with SARS. It was that public health response and medical scientific response were very good in 2003, and they’re getting better.
Going forward now, is there much we can do to get ahead of these dangers?
We can. It’s very hard to predict exactly what the next big one will be. The influenzas are mutating constantly, so that’s why we need a new influenza vaccine every year. It’s hard to predict, but vigilance — monitoring, fast and effective response — those dimensions are improving vastly.
Do we need to do a much better job of combining animal and human health studies, so we know what’s happening in wildlife before those viruses make the jump?
Absolutely, and that’s improving too. A lot of these people started as veterinarians, and they get a PhD in ecology, and then they get a masters in public health. Or maybe they come from the other direction, from the public health direction. Those fields are coming together, and it’s crucial that they do.
What prompted you to focus on this subject? You’ve written about conservation issues in the past. Was this an extension of that?
What grabbed my attention was sitting at a campfire literally 12 years ago this summer in central Africa, hearing some Bantu guys talk about the time when Ebola struck their village and was killing their friends and loved ones. And they described it very vividly to me around this campfire, and then one of them said, “Oh yeah and by the way, when Ebola was tearing our village apart, we saw a pile of 13 dead gorillas nearby in the forest.” And I knew that Ebola kills gorillas and chimps as well as humans, but that brought it home, that this is a phenomenon about connectedness. This is a reminder that humans are animals too, that we share diseases with animals, we share our fate with animals. We’re part of the natural world, and it’s really made dramatic and vivid and important by the subject of zoonotic diseases.
You spent a lot of time out in the field with scientists who are actually doing this work. Any particular stories from that time that stuck with you?
I’ve had some interesting times. There was a young Congolese doctor who was assigned the task of going out when a chimpanzee carcass or a gorilla carcass was discovered in the Gabonese forest. His job was to get out there as quickly as possible and take tissue samples from that dead ape to see if it tested positive for Ebola. So he would dress in a moon suit and snip some organ material out of this rotting chimp carcass. And there was one day when he did that and there were bees all over this thing. And the bees went charging up his arms and underneath his hood — which was not a sealed hood, it just a positive air pressure, so it was being vented from under this sort of cowl. The bees charged up underneath this cowl and down across his body and started stinging him. So he’s sitting there thinking, “Great, am I going to get Ebola from a bee sting that just came off of a chimp carcass?” As it turned out, he did not. And he sort of laughed his charming nervous laugh when he told me about this. Then I asked, “Why are you doing this work — why do you continue doing it?” And he said, “Well, because I’ve learned enough to be careful, and because it’s important, and because it’s really interesting.”
MORE: 10 Terrible Epidemics