Scientists in Canada and the US may have found a way of containing the world's deadliest diseases.

They report that new vaccines have proved 100% effective against infection from the Ebola and Marburg viruses in laboratory monkeys.

Both viruses destroy blood vessel cells, causing internal bleeding. In the end, the victim becomes little more than a bag of blood. Both diseases are very infectious, highly lethal, endemic in tropical Africa -and could one day become weapons for bioterrorism.

"When you see the tragedies these viruses cause, it's very frustrating that we can't do more to help people," said Heinz Feldmann of the Public Health Agency of Canada, who reports with colleagues in Nature Medicine today. "It will be some time before we can use these vaccines in the field, but it is satisfying to know we are getting closer."

Marburg takes its name from the German city in which it was first identified in 1967: the victims had all handled vervet monkeys from Uganda. The Canadian scientists are working with health officials in Angola, where there is a new outbreak of Marburg fever.

Ebola was first recorded in Zaire in 1976 when it infected more than 300 people, killing 90% of them. It is also a disease of primates, and an epidemic has reduced some gorilla populations in west Africa. World health chiefs have recorded at least 17 other outbreaks in the past 30 years.

The Canadians worked with scientists from the US army medical research institute of infectious diseases to devise one vaccine that worked effectively against both viruses in non-human primates.

"The vaccine targets dendritic cells, which are the same cells that Ebola and Marburg attack," said Thomas Geisbert of the US army. "These cells are also important in generating a protective immune response. So the vaccine goes exactly where we want it to go."

Canada's public health minister, Carolyn Bennett, said a successful vaccine would reduce "the risk that these viruses will be used in bioterrorism".