You've heard of Ebola and likely Zika, but there are many dangerous viruses that have yet to make horrific headlines. A panel of scientists and public health experts gathered by the World Health Organization (WHO) met to discuss the top emerging pathogens most likely to cause severe outbreaks in the near future. These are viruses for which there is no vaccine and few, if any, treatments.
Here's a look at these diseases and what makes them so frightening.
Editor's note: This gallery has been updated since it was originally published in June 2016.