The world's biggest and deadliest Ebola outbreak began with a 2-year-old boy in a village in Guéckédou, Guinea — near the West African country's borders with Sierra Leone and Liberia — a team of researchers reports in The New England Journal of Medicine. The boy died of unidentified causes on Dec. 6, followed a week later by his mother, then 3-year-old sister, then grandmother. Mourners at the grandmother's funeral brought the virus to other villages.
The early victims had symptoms of Ebola, but the outbreak is in a part of Africa with no history of the disease, so health workers weren't trained to spot or treat the disease. And because it's a heavily trafficked region, the disease has been very difficult to track down and isolate.
Doctors Without Borders helped identify and treat the outbreak in March, and health officials thought they had it contained by April. The outbreak flared up a month later, worse than ever — there are now officially 1,779 cases, including 961 deaths, but health authorities believe there are more cases. The World Health Organization has declared an international health emergency.
So how did the 2-year-old get the virus? "We suppose that the first case was infected following contact with bats," Sylvain Baize at France's Pasteur Institute, and one of the researchers studying the outbreak, tells The New York Times. "Maybe, but we are not sure." The blood of fruit bats, as well as monkeys and apes, can infect people, but some researchers think that fruit with bat guano on it can also spread the virus to humans.