National Geographic : 2015 Jul
40 national geographic • July 2015 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 crea- ture, 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. De- spite 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 inter- national 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 vil- lager, 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 le- thal 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 put- ting 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 tes- timony nor physical evidence of any remarkable deaths among chimpanzees or other large mam- mals. 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, Leen- dertz’s team ascertained that the villagers were probably talking about the Angolan free-tailed EBOLA IS NOT A SUBTLE BUG. IT KILLS MANY OF ITS HUMAN VICTIMS IN A MATTER OF DAYS, PUSHING OTHERS TO THE BRINK OF DEATH, BEFORE VANISHING.