A list of 37 viruses that pose a potential threat to populations around the world has been drawn up by experts.
All the infectious agents have shown some ability to spread between people but not so far caused a major epidemic.
Among those of greatest concern are MERS coronavirus, relatives of Ebola, and several mosquito-borne viruses, all of which have caused isolated disease outbreaks.
Currently these viruses are mostly confined to animals. But if they became able to pass more easily from person-to-person they could pose a serious danger, say the scientists.
The team used prediction methods already used to warn of the threat of Zika and Ebola before both sparked major epidemics.
Lead researcher Professor Mark Woolhouse, from the University of Edinburgh, said: "Monitoring these infections should be prioritised because relatively minor changes in their ecology could lead to major changes in the threat they pose to public health."
The scientists reviewed characteristics of the viruses, including what species they infect and how well they adapt to new hosts. They also considered the severity of the infections.
The study, published in the journal Emerging Infectious Diseases, was funded by the Wellcome Trust's Vietnam Initiative on Zoonotic Infections and the European Union Compare project.