Scientists who accidently created a deadly version of mouse smallpox in the laboratory say grave destructive human viruses are not far away.
Dr. Jim Hughes, director of the CDC said health officials needed better surveillance, greater diagnostic capacity and more communication between scientific disciplines, to respond to emerging threats.
"We feel it is prudent to be prepared to deal with the unexpected, whether it's a naturally occurring infectious disease or an episode that is a result of a purposeful release of an infectious agent," he said.
The CDC has emphasized the need to educate those who would have to deal with such attacks - doctors, hospital staff, firefighters and police. It says they need to be able to recognize the symptoms caused by the viruses - such as anthrax or smallpox.
The New Scientist magazine has reported the endeavour of Australian researchers who made one simple genetic change to a "mousepox" virus in an attempt to produce an effective contraceptive vaccine. "Mousepox" normally causes only mild illness, and when all the animals undergoing the experiment died within days, they realized the potential of their discovery.
They say a similar change in human smallpox could produce a far more virulent strain which could even be resistant to vaccines.
The idea was to stimulate an immune reaction against mouse eggs, with a contraceptive effect - but the effect was to completely suppress the part of the immune system normally mobilized to fight viral infection.
Smallpox infection is already believed to have an approximate mortality rate of 30% - an increase, coupled with the natural contagiousness of the virus, could be lethal, say experts.
Smallpox, a much feared disease in the 20th century, was eradicated by a massive vaccination programme. The disease presents as severe headache and fever, with the trademark sores appearing after a few days.
The last confirmed outbreak of smallpox was in 1977 in Somalia - later that year, the World Health Organisation declared the disease eradicated.