The first cases went unrecognized. Ebola had never been seen in Guinea before, so when people became ill with fever, muscle pain, vomiting, and diarrhea, health workers initially assumed Lassa fever or yellow fever—both endemic in the region—were to blame. No one put the pieces together until late March. By then, the virus had been spreading for months. Now, health workers are struggling to contain the outbreak, which has already killed more than 100 and has affected at least two neighboring countries. At the same time, scientists are combing the forests, and the genome of the virus itself, looking for clues to how this strain—well known in Central Africa—ended up so far west, and whether its spread suggests people in forested areas all across sub-Saharan Africa are at risk.
Ebola is not a complete stranger to West Africa. In the mid-1990s, two outbreaks hit chimpanzees in Taï National Park in the Ivory Coast, and one researcher studying the animals was infected. (She survived.) "We expected to find the Taï strain," says Sylvain Baize, a virologist at the Institut Pasteur in Lyon, France, who with his colleagues sequenced some of the first samples of the virus from Guinea. To their surprise, it turned out to be Ebola Zaire, the deadliest of the five known Ebola species.
"We have no idea how it's moved from Central Africa to Guinea," says primatologist Christophe Boesch of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. A leading suspect is fruit bats. In Central African rainforests, several species have shown evidence of infection with Ebola without getting sick. And at least one of the species, the little collared fruit bat, Myonycteris torquata, has a range that stretches as far west as Guinea. "We've always been very suspicious of bats," says William Karesh of EcoHealth Alliance in New York City, who studies the interactions among humans, animals, and infectious diseases.
Ebola virus graphic by Russell Kightley Media
Via Torben Barsballe