A number of additional diseases were discussed and considered for inclusion in the priority list, including: Arenaviral hemorrhagic fevers other than Lassa Fever; Chikungunya; highly pathogenic coronaviral diseases other than MERS and SARS; emergent non-polio enteroviruses (including EV71, D68); Severe Fever with Thrombocytopenia Syndrome (SFTS); Monkeypox and Leptospirosis.
The World Health Organisation (WHO) has put scientists and health workers around the globe on alert for a new and potentially deadly pathogen - Disease X.
Mr Rottingen said Disease X would most likely be sparked by a "zoonotic disease" jumps from animals to humans and then becomes an epidemic, which happened with H1N1 swine flu in 2009.
Every year, scientists at the World Health Organization create a list of the most likely diseases which have potential to break out into a worldwide pandemic.
Code-named "Disease X", this mystery pathogen hasn't even been discovered yet, but the looming threat of its nearly certain inevitability has secured it a place on the WHO's "most dangerous" list: a catalogue of potential future epidemics for which countermeasures are insufficient - or don't exist at all.
The release of the priority list comes as WHO also revealed it has developed a special tool to identify diseases that pose a widespread health risk.
According to experts, Disease X, in all probabilities will be man-made.
"It may seem odd to be adding an "X" but the point is make sure we prepare and plan flexibly in terms of vaccines and diagnostic tests".
"History tells us that it is likely the next big outbreak will be something we have not seen before", chief executive of the Research Council of Norway and World Health Organization adviser John-Arne Rottingen told The Telegraph.
"It's a natural process and it is vital that we are aware and prepare". However, it also warned that these pathogens still pose a serious risk to public health, and should be "watched carefully".
Whatever the case may be, the WHO hopes its list will spur governments across the globe to invest more into strengthening local health systems.
Given the rapid development of gene-editing technologies, Disease X could also spring up from human error or malevolence - in which case, having a flexible, widely-applicable plan of action is of paramount importance. Marion Koopmans, WHO adviser, said, "The intensity of animal and human contact is becoming much greater as the world develops".