The World Health Organisation (WHO) has warned the world to expect a new killer disease to emerge in the next few years which will threaten the lives of millions.
The WHO says the new disease will have the impact of HIV/AIDS or Ebola and potentially deadly new diseases are being identified at an "unprecedented rate" with at least one new disease identified every year since the 1970s.
There are now 39 more diseases that were unknown just over a generation ago and the WHO says global epidemics are spreading more rapidly than ever.
The warning comes as part of the United Nations agency's annual world health report and WHO director general, Margaret Chan, says the world is vulnerable.
New diseases are apparently emerging at an historically unprecedented rate of one per year and Dr. Chan says governments worldwide must be on guard for new threats such as that presented by SARS (severe acute respiratory syndrome) in 2003, which spread from China to 30 countries and killed 800 people along the way.
The UN agency says infectious diseases are spreading faster due to global travel and a worldwide market in live animals; more than 1,100 epidemics have been verified in the last five years, including bird flu, cholera and polio.
The WHO says it would be naive and complacent in the extreme to assume that there will not be another disease such as AIDS, Ebola, or SARS, sooner or later.
There are now more than 2 billion global air travellers each year, says the WHO and this means an outbreak or epidemic in one part of the world is only a few hours away from becoming an imminent threat somewhere else.
The report, "A Safer Future", says stricter monitoring of diseases prone to becoming epidemics, such as cholera and yellow fever, is called for with more help for poorer countries in identifying emerging viral diseases such as Ebola and Marburg haemorrhagic fever.
The agency maintains the next influenza pandemic is likely to be a bird flu one which could affect around 1.5 billion people and the question is one of when rather than whether.
Governments across the world have been asked to plan for its arrival and many have stockpiled flu vaccine in readiness.
The WHO warns that global efforts to control infectious diseases had been "seriously jeopardised" by the rise in drug-resistant strains of diseases, and the culprits are poor medical treatment and misuse and overuse of antibiotics.