Translator: Clement Fu
Reviewer: Tanya Cushman Twelve years ago, I heard a phrase
that changed my life, really. I was sitting at a campfire
in Central Africa, and the phrase was this: "Thirteen dead gorillas." I didn't realize at the time, but that phrase was launching me
on a long quest. It was a quest to understand the ecology
and evolutionary biology of scary viruses. Does virus even have an ecology? Yeah. Can a virus evolve? Yes. Why should we care? Because those subjects
relate to the matter of whether tens of millions
of people might die in the next new pandemic disease. This quest took me out of my comfort zone. My comfort zone up until then
was big critters, writing about critters that you can see. And then I found myself
at this particular campfire. We were in the midst of a forest
in northeastern Gabon, and these two local guys
were talking about Ebola virus. They were talking about the time
Ebola struck their village, not very many miles
from where we were sitting. It was a terrible outbreak, killed dozens of their loved ones
and friends in hideous ways. They seemed traumatized by the memories, but I was prying the story out of them. And then one of them said, "You know, besides all the death and misery
in the village, there was something else, something strange right at that time, something we saw. It was a pile of 13 dead gorillas
lying nearby in the forest." 13 dead gorillas in a pile. I think my mouth fell open. I wrote the phrase in my notebook. I already knew a bit about Ebola, and one thing I knew is that it kills
gorillas and chimps as well as humans, but hearing that phrase from them
in the midst of Ebola habitat made the whole thing more immediate. It was the beginning of my quest
to understand something called "zoonosis." Zoonosis - kind of a technical term,
but it's easy to define. A zoonosis is an animal infection
transmissible to humans: might be a virus like Ebola or Marburg, might be a bacterium like the bug
responsible for Lyme disease. Once it gets into humans, if it takes hold and causes sickness,
we call that a zoonotic disease. Now, this is not a small subject
at the weird fringe of medicine. This is central. 60% of the infectious diseases
known among humans are zoonotic. Bubonic plague is a zoonotic disease:
it passes from rodents into people. AIDS is a disease of zoonotic origin, caused by a virus that passed from a single chimpanzee
into a single human back around 1908,
give or take a margin of error. Hendra is a very nasty zoonotic virus
that falls out of bats into horses, killing them, and then goes from horses
into people, killing them. These zoonoses, for all their bad effects, they serve one valuable purpose: they remind us of the connectedness between humans and other species. And one form of that connectedness is shared disease. Animal disease, human disease - same disease. So just thinking about zoonosis
tends to reaffirm the old Darwinian truth, and it's probably
the darkest of his truths, that we humans are animals, we're part of nature, we're not separate from it
or somehow above it. There are a lot of new entries
to the grim list of zoonoses. Most of them are viruses. They've emerged and caused outbreaks, one after another, over the last five or six decades: Machupo, in Bolivia, 1961; Marburg, related to Ebola, 1967; Ebola itself hit
the radar screens in 1976; HIV, first recognized 1981; Hanta, in America, 1993; Hendra, in Australia, 1994; Bird flu, Hong Kong, 1997; Nipah virus, in Malaysia, 1998; West Nile, New York, 1999; and SARS, coming out
of southern China, 2003. You get the picture. It's been a drumbeat of new viruses emerging over recent years. If they're emerging, emerging from where? Every new zoonotic disease
starts as a mystery story: we can guess that the infection crosses
into humans from some other animal, but which animal? Another technical term here: any species in which a zoonotic bug
lives permanently, inconspicuously, without causing symptoms is known as the "reservoir host." Bats are the reservoir hosts
for Hendra virus. The reservoir host of Ebola
is still undiscovered, but we know that Marburg, Ebola's cousin,
also has its reservoir in bats. And the hantaviruses
come to us from rodents. Okay, one final bit of terminology: when a zoonotic bug
passes from its reservoir host into its first human victim, that event is called "spillover." Geoffrey Platt in an isolation ward. Spillover, okay. So now you've got the basics,
the crucial ideas and the key terms: zoonosis, reservoir host, spillover. With that much, you understand more
about the future of infectious disease than 99% of the human population. Pat yourselves on the back
and get a flu shot in November. (Laughter) Why are all these spillovers occurring? Why are some of them
quickly circling the world? I can answer in two words:
disruption and connectivity. More and more, we humans
are disrupting the wild diverse ecosystems that harbour so many
different kinds of creature. And for each species
of animal or plant in those places, there's probably at least
one unique form of virus. All of our logging and burning
and road building and settlement and killing and eating of bushmeat, all of those actions tend to shake loose
new viruses from the reservoir hosts, giving them the opportunity
to infect humans instead - disruption. And once they infect us, once they enter, replicate, adapt, and find ways to transmit
from human to human, they can travel
with the speed of an airplane, killing millions of people along the way. Seven years ago, National Geographic
asked me to do a story on this subject. They sent me back to Central Africa,
sent me to a number of other places. That magazine assignment
turned into a book project. The book was finally published
last autumn [2012]. It's a compendium of gruesome stories
and scientific ideas, but it's also the tale of this quest, my quest to understand
the dynamics and the human realities of zoonotic diseases. From the campfire in Central Africa
until this afternoon, that quest has consumed
12 years, 8 months and 11 days - I haven't added up the miles. But the real effort has just begun. The real effort involves trying
to persuade you and other people of the deeper meaning of zoonotic disease. The deeper meaning is more
than just preventing human illness; it goes back to that
basic Darwinian truth. The deeper meaning is that people and gorillas,
chimps and monkeys and horses, rodents and bats and viruses - we are all in this together. Thank you. (Applause)
