External Link - Source: Science
The sheer size of the Ebola epidemic that began in 2013 and engulfed West Africa is still a bit of a riddle for scientists. Previous Ebola outbreaks had never sickened more than 600 people. But the outbreak in Liberia, Sierra Leone, and Guinea infected more than 28,000 before it was finally brought under control. Part of the explanation was that the virus had suddenly surfaced in major cities, making it harder to stamp out than in the isolated rural locales where it had struck before. The countries’ poor public health infrastructure and other environmental factors played roles as well.