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Seeking the Source of Ebola
The latest Ebola crisis may yield clues about where it hides between outbreaks.
By David Quammen
Photographs by Pete Muller
No one foresaw, back in December of 2013, that the little boy who fell ill in a village called Méliandou, in Guinea, West Africa, would be the starting point of a gruesome epidemic, one that would devastate three countries and provoke concern, fear, and argument around the planet.
No one imagined that this child’s death, after just a few days’ suffering, would be only the first of many thousands. His name was Emile Ouamouno. His symptoms were stark—intense fever, black stool, vomiting—but those could have been signs of other diseases, including malaria. Sad to say, children die of unidentified fevers and diarrheal ailments all too frequently in African villages. But soon the boy’s sister was dead too, and then his mother, his grandmother, a village midwife, and a nurse. The contagion spread through Méliandou to other villages of southern Guinea. This was almost three months before the word “Ebola” began to flicker luridly in email traffic between Guinea and the wider world.
The public health authorities based in Guinea’s capital, Conakry, and the viral disease trackers from abroad weren’t in Méliandou when Emile Ouamouno died. Had they been, and had they understood that he was the first case in an outbreak of Ebola virus disease, they might have directed some timely attention to an important unknown: How did this boy get sick? What did he do, what did he touch, what did he eat? If Ebola virus was in his body, where did it come from?
Among the most puzzling aspects of Ebola virus, since its first recognized emergence almost four decades ago, is that it disappears for years at a time. Since a 1976 outbreak in what then was Zaire (now the Democratic Republic of the Congo) and a simultaneous episode with a closely related virus in what was then southern Sudan (now South Sudan), the sequence of Ebola events, large and small, has been sporadic. During one stretch of 17 years (1977-1994) not a single confirmed human death from infection with Ebola virus occurred. This is not a subtle bug that simmers delicately among people, causing nothing more than mild headaches and sniffles. If it had been circulating in human populations for those 17 years, we would have known.
A virus can’t survive for long, or replicate at all, except within a living creature. That means it needs a host—at least one kind of animal, or plant, or fungus, or microbe, whose body serves as its primary environment and whose cell machinery it can co-opt for reproducing. Some harmful viruses abide in nonhuman animals and only occasionally spill into people. They cause diseases that scientists label zoonoses. Ebola is a zoonosis, an especially nasty and perplexing one—killing many of its human victims in a matter of days, pushing others to the brink of death, and then vanishing. Where does it hide, quiet and inconspicuous, between outbreaks?
Not in chimpanzees or gorillas; field studies have shown that Ebola often kills them too. Dramatic die-offs of chimps and gorillas have occurred around the same time and in the same area as Ebola virus disease outbreaks in humans, and some carcasses have tested positive for signs of the virus. Scavenging ape carcasses for food, in fact, has been one of the routes by which humans have infected themselves with Ebola. So the African apes are highly unlikely to harbor Ebola. It hits them and explodes. It must lurk somewhere else.
The creature in which a zoonotic virus exists over the long term, usually without causing symptoms, is known as a reservoir host. Monkeys serve as reservoir hosts for the yellow fever virus. Asian fruit bats of the genus Pteropus are reservoirs of Nipah virus, which killed more than a hundred people during a 1998-99 outbreak in Malaysia. Fruit bats also host Hendra virus in Australia, where it drops from bats into horses, with devastating effect, and then into horse handlers and veterinarians, often killing them. The passage event, when a virus goes from its reservoir host to another kind of creature, is termed spillover.
As for the reservoir host of Ebola—if you have heard that fruit bats again are the answer, you’ve heard supposition misrepresented as fact. Despite arduous efforts by some intrepid scientists, Ebola virus has never been tracked to its source in the wild.
“Where is it when it’s not infecting humans?” Karl M. Johnson said to me recently. Johnson is an eminent virologist, a pioneer in Ebola research, the former head of the Viral Special Pathogens Branch at the Centers for Disease Control and Prevention (CDC). He led the international response team against that initial 1976 outbreak in Zaire, a harrowing venture into the unknown. He also led a team that isolated the virus in a CDC lab, demonstrated that it was new to science, and named it after a modest Zairean waterway, the Ebola River. Johnson wondered back then about its hiding place in the wild. But the urgency of human needs during any Ebola outbreak makes investigations in viral ecology difficult and unpopular. If you’re an African villager, you don’t want to see foreigners in moon suits methodically dissecting small mammals when your loved ones are being hauled away in body bags. Thirty-nine years later, although we’re beginning to learn a bit, Johnson said, the identity of the reservoir host “is still largely a monster question mark out there.”
A Rain of Bats
In April 2014, soon after word spread that the cluster of deaths in southern Guinea involved Ebola, Fabian Leendertz arrived there with a team of researchers. Leendertz is a German disease ecologist and veterinarian, based at the Robert Koch Institute in Berlin, who studies lethal zoonoses in wildlife, with special attention to West Africa. He reached southern Guinea by driving overland from Ivory Coast, where he has worked for 15 years in Taï National Park on disease outbreaks among chimpanzees and other animals. He brought with him three big vehicles, full of equipment and people, and two questions. Had there been a recent die-off among chimps or other wildlife, possibly putting meat-hungry humans at risk from infected carcasses? Alternatively, had there been direct transmission from the Ebola reservoir host, whatever it was, into the first human victim? Leendertz knew nothing at that point about Emile Ouamouno. His team spoke with officials and local people and walked survey transects through two forest reserves, finding neither testimony nor physical evidence of any remarkable deaths among chimpanzees or other large mammals. Then they shifted their attention to the village of Méliandou, talked with people there, and heard a very interesting story about a hollow tree full of bats.
These were small bats, the quick-flying kind that echolocate and feed on insects, not the big creatures that fly out majestically at dusk, like a Halloween vision of nocturnal crows, to eat fruit. The locals called them lolibelo. They were dainty as mice and smelly, with wriggly tails that extended beyond their hind membranes. Showing pictures and taking descriptions, Leendertz’s team ascertained that the villagers were probably talking about the Angolan free-tailed bat (Mops condylurus). These bats had roosted in great numbers within a big, hollow tree that stood beside a trail near the village. Then, just weeks before, the tree had been burned, possibly during an attempt to gather honey. From the burning tree came what the people remembered as “a rain of bats.” The dead bats were gathered up, filling a half dozen hundred-pound rice sacks, and might have been eaten except for a sudden announcement from the government that because of Ebola, consuming bush meat was now prohibited. So the Méliandou villagers threw the dead bats away.
And there was something else about that hollow tree, the villagers told Leendertz’s team. Children, possibly including Emile Ouamouno, used to play in it, sometimes catching the bats. They would even roast them on sticks and eat them.
Leendertz consulted a colleague with expertise in recovering DNA from environmental samples, who told him it might be feasible to find enough beneath the tree to identify the bat species that had roosted there. “So I started running around with my tubes and spoon collecting soil,” Leendertz told me. Back in Berlin, genetic sequencing confirmed the presence of Angolan free-tailed bats. So this creature—an insectivorous bat, not a fruit bat—joined the list of candidates for the role of Ebola’s reservoir host.
The Hitchhiker
The first clues in this long mystery—clues that seemed to point toward bats—arose from disease outbreaks caused by Marburg virus, Ebola’s slightly less notorious relative within the group known as filoviruses. The story of Ebola is closely connected with that of Marburg, according to a seasoned South African virologist named Robert Swanepoel, who has long studied them both.
“The two are interlinked,” he said, as we sat before a computer screen in his Pretoria home, looking at photographs from his archive. Swanepoel, who hides a genial heart within a bearish exterior, is retired from the National Institute for Communicable Diseases (NICD), in Johannesburg, where he ran the Special Pathogens Unit for 24 years, but is still busy with research and bristling with ideas and memories.
...
Seeking the Source of Ebola
The latest Ebola crisis may yield clues about where it hides between outbreaks.
By David Quammen
Photographs by Pete Muller
No one foresaw, back in December of 2013, that the little boy who fell ill in a village called Méliandou, in Guinea, West Africa, would be the starting point of a gruesome epidemic, one that would devastate three countries and provoke concern, fear, and argument around the planet.
No one imagined that this child’s death, after just a few days’ suffering, would be only the first of many thousands. His name was Emile Ouamouno. His symptoms were stark—intense fever, black stool, vomiting—but those could have been signs of other diseases, including malaria. Sad to say, children die of unidentified fevers and diarrheal ailments all too frequently in African villages. But soon the boy’s sister was dead too, and then his mother, his grandmother, a village midwife, and a nurse. The contagion spread through Méliandou to other villages of southern Guinea. This was almost three months before the word “Ebola” began to flicker luridly in email traffic between Guinea and the wider world.
The public health authorities based in Guinea’s capital, Conakry, and the viral disease trackers from abroad weren’t in Méliandou when Emile Ouamouno died. Had they been, and had they understood that he was the first case in an outbreak of Ebola virus disease, they might have directed some timely attention to an important unknown: How did this boy get sick? What did he do, what did he touch, what did he eat? If Ebola virus was in his body, where did it come from?
Among the most puzzling aspects of Ebola virus, since its first recognized emergence almost four decades ago, is that it disappears for years at a time. Since a 1976 outbreak in what then was Zaire (now the Democratic Republic of the Congo) and a simultaneous episode with a closely related virus in what was then southern Sudan (now South Sudan), the sequence of Ebola events, large and small, has been sporadic. During one stretch of 17 years (1977-1994) not a single confirmed human death from infection with Ebola virus occurred. This is not a subtle bug that simmers delicately among people, causing nothing more than mild headaches and sniffles. If it had been circulating in human populations for those 17 years, we would have known.
A virus can’t survive for long, or replicate at all, except within a living creature. That means it needs a host—at least one kind of animal, or plant, or fungus, or microbe, whose body serves as its primary environment and whose cell machinery it can co-opt for reproducing. Some harmful viruses abide in nonhuman animals and only occasionally spill into people. They cause diseases that scientists label zoonoses. Ebola is a zoonosis, an especially nasty and perplexing one—killing many of its human victims in a matter of days, pushing others to the brink of death, and then vanishing. Where does it hide, quiet and inconspicuous, between outbreaks?
Not in chimpanzees or gorillas; field studies have shown that Ebola often kills them too. Dramatic die-offs of chimps and gorillas have occurred around the same time and in the same area as Ebola virus disease outbreaks in humans, and some carcasses have tested positive for signs of the virus. Scavenging ape carcasses for food, in fact, has been one of the routes by which humans have infected themselves with Ebola. So the African apes are highly unlikely to harbor Ebola. It hits them and explodes. It must lurk somewhere else.
The creature in which a zoonotic virus exists over the long term, usually without causing symptoms, is known as a reservoir host. Monkeys serve as reservoir hosts for the yellow fever virus. Asian fruit bats of the genus Pteropus are reservoirs of Nipah virus, which killed more than a hundred people during a 1998-99 outbreak in Malaysia. Fruit bats also host Hendra virus in Australia, where it drops from bats into horses, with devastating effect, and then into horse handlers and veterinarians, often killing them. The passage event, when a virus goes from its reservoir host to another kind of creature, is termed spillover.
As for the reservoir host of Ebola—if you have heard that fruit bats again are the answer, you’ve heard supposition misrepresented as fact. Despite arduous efforts by some intrepid scientists, Ebola virus has never been tracked to its source in the wild.
“Where is it when it’s not infecting humans?” Karl M. Johnson said to me recently. Johnson is an eminent virologist, a pioneer in Ebola research, the former head of the Viral Special Pathogens Branch at the Centers for Disease Control and Prevention (CDC). He led the international response team against that initial 1976 outbreak in Zaire, a harrowing venture into the unknown. He also led a team that isolated the virus in a CDC lab, demonstrated that it was new to science, and named it after a modest Zairean waterway, the Ebola River. Johnson wondered back then about its hiding place in the wild. But the urgency of human needs during any Ebola outbreak makes investigations in viral ecology difficult and unpopular. If you’re an African villager, you don’t want to see foreigners in moon suits methodically dissecting small mammals when your loved ones are being hauled away in body bags. Thirty-nine years later, although we’re beginning to learn a bit, Johnson said, the identity of the reservoir host “is still largely a monster question mark out there.”
A Rain of Bats
In April 2014, soon after word spread that the cluster of deaths in southern Guinea involved Ebola, Fabian Leendertz arrived there with a team of researchers. Leendertz is a German disease ecologist and veterinarian, based at the Robert Koch Institute in Berlin, who studies lethal zoonoses in wildlife, with special attention to West Africa. He reached southern Guinea by driving overland from Ivory Coast, where he has worked for 15 years in Taï National Park on disease outbreaks among chimpanzees and other animals. He brought with him three big vehicles, full of equipment and people, and two questions. Had there been a recent die-off among chimps or other wildlife, possibly putting meat-hungry humans at risk from infected carcasses? Alternatively, had there been direct transmission from the Ebola reservoir host, whatever it was, into the first human victim? Leendertz knew nothing at that point about Emile Ouamouno. His team spoke with officials and local people and walked survey transects through two forest reserves, finding neither testimony nor physical evidence of any remarkable deaths among chimpanzees or other large mammals. Then they shifted their attention to the village of Méliandou, talked with people there, and heard a very interesting story about a hollow tree full of bats.
These were small bats, the quick-flying kind that echolocate and feed on insects, not the big creatures that fly out majestically at dusk, like a Halloween vision of nocturnal crows, to eat fruit. The locals called them lolibelo. They were dainty as mice and smelly, with wriggly tails that extended beyond their hind membranes. Showing pictures and taking descriptions, Leendertz’s team ascertained that the villagers were probably talking about the Angolan free-tailed bat (Mops condylurus). These bats had roosted in great numbers within a big, hollow tree that stood beside a trail near the village. Then, just weeks before, the tree had been burned, possibly during an attempt to gather honey. From the burning tree came what the people remembered as “a rain of bats.” The dead bats were gathered up, filling a half dozen hundred-pound rice sacks, and might have been eaten except for a sudden announcement from the government that because of Ebola, consuming bush meat was now prohibited. So the Méliandou villagers threw the dead bats away.
And there was something else about that hollow tree, the villagers told Leendertz’s team. Children, possibly including Emile Ouamouno, used to play in it, sometimes catching the bats. They would even roast them on sticks and eat them.
Leendertz consulted a colleague with expertise in recovering DNA from environmental samples, who told him it might be feasible to find enough beneath the tree to identify the bat species that had roosted there. “So I started running around with my tubes and spoon collecting soil,” Leendertz told me. Back in Berlin, genetic sequencing confirmed the presence of Angolan free-tailed bats. So this creature—an insectivorous bat, not a fruit bat—joined the list of candidates for the role of Ebola’s reservoir host.
The Hitchhiker
The first clues in this long mystery—clues that seemed to point toward bats—arose from disease outbreaks caused by Marburg virus, Ebola’s slightly less notorious relative within the group known as filoviruses. The story of Ebola is closely connected with that of Marburg, according to a seasoned South African virologist named Robert Swanepoel, who has long studied them both.
“The two are interlinked,” he said, as we sat before a computer screen in his Pretoria home, looking at photographs from his archive. Swanepoel, who hides a genial heart within a bearish exterior, is retired from the National Institute for Communicable Diseases (NICD), in Johannesburg, where he ran the Special Pathogens Unit for 24 years, but is still busy with research and bristling with ideas and memories.
...