(MailOnline) A lethal new virus which kills humans has been developed by scientists as part of a US government project.
The genetically modified variant of smallpox is so dangerous that, as yet, no vaccination can combat it.
The virus was discovered while scientists were working on a lethal form of mousepox.
This killed 100 per cent of mice even if they had been given anti-viral drugs as well as a vaccine that would normally protect them.
The same techniques were then used to genetically alter the cowpox virus, which infects a range of animals including humans, by scientists at the University of St Louis.
Their research brings closer the prospect of pox viruses being turned into lethal new diseases even when people have been vaccinated.
Mark Buller, who led the research, told New Scientist magazine his work was necessary to second guess what bioterrorists might be able to do in future.
Bio-terror is seen as a risk in the West since the September 11 terror attacks and the anthrax scare that followed.
Five people were killed and 17 others were left seriously ill in anthrax attacks in the US in October 2001.
But other scientists, such as Ian Ramshaw of the Australian National University, said the American team’s work could prove dangerous if the knowledge fell into the wrong hands.
‘I have great concern about doing this in a pox virus that can cross species,’ he added.
Dr Ramshaw was among a group of scientists who accidentally discovered how to make mousepox more deadly three years ago while developing contraceptives for mice. This strain, which was was not as dangerous as Dr Buller’s, killed 60 per cent of mice.