We still don't know for sure how Ebola reached humans

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Marco Werman: Scientists think they know how Ebola started -- in wild bats living in the forest of Central Africa. But they’re not entirely sure about that and some have ventured deep into those forests to try and find out what other creatures the disease has targeted.


David Quammen: We walked for about 10 days through this forest. It was very pristine, there was no sign of humans having been in there. It was beautiful gorilla habitat. And yet for 10 days, we saw no gorillas whatsoever.


Werman: That’s science writer David Quammen. His latest book is “Ebola: The Natural and Human History of a Deadly Virus.” In it, Quammen describes sitting down with villagers from a forest town in Gabon, where Ebola had struck more than two decades ago.


Quammen: One evening, I was sitting at a campfire with two of those guys and they started telling me what it had been like when Ebola hit their village, killing their friends and loved ones -- terrifying, they didn’t understand really what was happening. One of them said “And it was a strange thing -- at the same time nearby in the forest, we saw a pile of 13 dead gorillas.”


Werman: When you heard that, what did you think?


Quammen: Well, I knew that Ebola kills gorillas and chimps, as well as humans. So, when he said “13 dead gorillas” I realized that that was probably the reason we were seeing no gorillas in this forest. Ebola had swept through the forest, as well as the village, killing gorillas, as well as people. That was the point in time when I got interested in this whole subject of what we call zoonotic diseases -- diseases that pass from nonhuman animals into humans, diseases that we share with other species, including Ebola.


Werman: What have gorillas and chimps taught us then about Ebola over the years?


Quammen: They haven’t taught us enough because we haven’t solved the mystery of how they get sick. That outbreak that I mentioned, for instance, began when some boys went out hunting from the village and they came back with a dead chimpanzee, as though they were great hunters. Everyone in the village partook of the chimpanzee -- people eat chimpanzee and gorilla in some of these parts of Central Africa. Everyone who touched the chimpanzee or ate parts of the chimpanzee got sick with Ebola. So, we learned from that that Ebola can come through these intermediate hosts, chimps or gorillas, but they can’t be the reservoir host because it kills them too quickly, they’re as susceptible to it as we are. So, there has to be some other creature in which the virus hides for years at a time between these dramatic spillovers, and we’re still trying to figure out what that creature is.


Werman: So the host, or reservoir as you call it, for Ebola is still unknown but it’s thought to be not a primate but we’ve been hearing a lot about fruit bats. That’s still the focus now -- or now the focus?


Quammen: The actual scientific evidence is not there to make us positive that fruit bats are the reservoir hosts. There’s one fruit bat in particular, the hammer headed bat, that has been shown to carry antibodies to Ebola. That means simply that it has been exposed to Ebola virus, but that doesn’t necessarily mean that the virus lives in it, thrives in it, replicates abundantly in it and then spills over into other creatures. The acid test, the gold standard for identifying a reservoir host, is to isolate live virus from that particular species. That has not yet been done with Ebola. Nobody has isolated live virus from any animal in the forests of Central Africa, so we still don’t know for sure.


Werman: Isolate the live virus but not -- obviously you don’t want to kill the fruit bats, do you?


Quammen: No, bad idea, because those bats perform other important functions within their ecosystem. We probably couldn’t eradicate them if we tried without destroyed the forests entirely. So, the solution is that we have to identify the reservoir host and then educate people, give people options so that they don’t come in contact, meaning hunt, kill, eat the reservoir host of Ebola, whatever it is.


Werman: One of the characters in your book is a Congolese man named [???]. His job, he finds dead gorillas and chimps in the forest and takes tissue samples of them. Why is that important?


Quammen: [???] is a wonderful young Congolese veterinarian, courageous and passionate about his work, and he does that -- he looks for dead gorillas, dead chimps lying in the forest, follows reports, gets to them as quickly as he can, puts on his hazmat suit and takes tissue samples to look for signs of Ebola virus. It’s important because it will help us solve this whole mystery of “What is Ebola doing? Where is it living in the forest? Who is it infecting? What is it infecting? Is it passing like a pandemic through all of the gorillas in Central Africa and killing them? If so, is that why it’s causing outbreaks among people in different areas in Central Africa and now West Africa?” There are no lowland gorillas in the areas of West Africa where this outbreak began, but there are chimpanzees not far away.


Werman: It occurs to me why these people are doing this work, like [???], going into the jungles, doing harrowing things in bat-infested caves with cobras. Why do they do this work?


Quammen: These scientists are fascinated by Ebola virus because it is such a simple organism and yet it is so dangerous, so powerful, so virulent and they want to understand it. But they’re also acutely aware of the fact that it kills people and causes misery and they want to help that. So it combines scientific curiosity with selfless humanitarian dedication.


Werman: David Quammen’s latest book is called “Ebola: The Natural and Human History of a Deadly Virus.”