An American missionary has tested positive for Ebola as the death toll from an outbreak in central Africa has risen sharply, according to health experts. The head of the World Health Organization is expressing concern over the “scale and speed" of the epidemic, while the Congolese Ministry of Health reports that at least 131 people are believed to have been killed and 531 suspected to have been infected in the latest outbreak. Here's what we know. #ebola #outbreak #virus #disease #health