An unknown and deadly new illness dubbed Disease X has been added to the list of potential global epidemics that could potentially kills millions.
Each year scientists with the World Health Organisation (WHO) create a list of the most likely diseases to break out into a worldwide pandemic.
This year, among the familiar Ebola, SARS, and Zika viruses is the new name of Disease X.
And unlike the other pathogens, it is not known what causes Disease X or how doctors could try to treat it.
Researchers said that they added Disease X to the threat list to recognise the fact that the next deadly pandemic could be started by an illness that has not caused any problems before.