Q&A: The globalization of infectious disease

David Quammen has made his career writing about nature. A former Rhodes Scholar and novelist, he spent 15 years writing the “Natural Acts” column for Outside Magazine, getting an on-the-job education in ecology, biology, and evolution. In 1997, he published his first non-fiction bestseller, “The Song of the Dodo,” an exploration of geography and evolution. We recently discussed his latest book, “Spillover”, about diseases that spread from animals to humans. This phenomenon is called zoonosis, and it is increasing as humanity seeps further into undisturbed habitats.

The following is an edited and condensed version of a conversation with Quammen.

What was your motivation for writing a book about infections that travel between species?

I was sitting at a campfire in a forest in central Africa and a couple of local Bantu guys started talking to me about the time when Ebola virus hit their village and started killing their friends and loved ones. One of these fellas said to me, “You know, a peculiar thing, at the time that this terrible outbreak hit our village, we noticed a pile of thirteen dead gorillas nearby in the forest.” So that moment, that phrase “thirteen dead gorillas,” has just stuck in my mind for the past twelve years. It represented the connectedness of humans with other forms of life through our shared diseases.

Ebola spills out of some reservoir host, some species that it lives in inconspicuously, and it gets into chimps, it gets into gorillas, it gets into humans, and makes them all deathly sick. That was the point when I started thinking, well, maybe it’s time to write a book on that subject.

How does human progress put us at risk for new zoonotic outbreaks?

The point is there are two factors here at work, disruption and connectivity. Disruption is what I mentioned in the book about us making incursions into the wild places: cutting down tropical forests, killing and eating the animals, building roads, villages and timber camps – coming disruptively in contact with wild species. Virtually every animal, plant, fungus or bacterium is going to be carrying some unique species of virus. So the more we disrupt those places, those creatures, the more we bring ourselves in contact with those viruses and disrupt the equilibrium of those viruses within their natural hosts. That’s what exposes us to these new pathogens.

The connectivity part is the fact that the human population is not only so huge but also so interconnected now. Seven billion of us! Many of us living in big concentrations of huge cities, densely packed together. And traveling! Traveling around the world in a matter of hours. That connectivity is what creates greater potential for disease outbreaks to turn into pandemics.

How do some diseases amplify so catastrophically when they spill into new species?

It’s not known entirely, but presumably a virus that lives in a reservoir host has lived in those types of hosts for millions of years without causing any really noticeable illness. This is probably because they have lived there for such a long time. And then when they spill over into a new host, it’s like an animal colonizing a new ecosystem. In some cases those species that are new to those ecosystems cause a lot of havoc because they’ve left their natural limitations — their own competitors and predators — behind. And that parallels what these viruses can do in a new host.

What is the global potential for a new zoonotic outbreak?

This is not just something that’s happening in central Africa, it’s not just something that’s happing in southern China. It’s also happening in California, it’s happening in Texas, it’s happening in Connecticut. It’s not something far away and remote – it’s something that occurs virtually everywhere on this planet. And when it occurs, it travels.