Researchers at the Pasteur Institute in France said they had found evidence of the virus in a shrew and six rodents in Central African Republic.

Previously, the virus had only been found in primates and humans, and scientists had been scouring rainforests to find evidence of it in smaller mammals so they could work out where it came from and how it spread.

"The study should help research toward finding the natural reservoir of the Ebola virus," a spokesman said.

"It helps to better pinpoint areas where infected animals may be found and suggests new strategies for the detection of the virus."

90% die

Ebola causes haemorrhagic fever in humans. It's potential to destroy whole communities first came to scientists' attention in the mid 1970s, when severe outbreaks in Sudan and the former Zaire killed a total of approximately 440 people.

Traces of the Zaire strain of the virus were found

The Zaire strain of the virus is the most deadly to date, proving fatal in just under 90% of those who contracted it.

The French researchers - based in Paris and the Central African Republic capital Bangui - found traces of the virus identical to Ebola strains isolated in the former Zaire and Gabon in the animals.

They did not find any live virus, but using molecular biology techniques were able to find viral sequences in the apparently healthy animals.

Re-working theories

The animals were caught at ground level - casting doubt on current theory that the virus is spread by flying mammals.

"This work provides evidence that different rodent species and one shrew species have been in contact with the Ebola virus - terrestrial species are concerned, contrary to the current hypothesis," the spokesman said.

"In addition, these results fit well with the history of fauna in tropical Africa. They show that there is a common Ebola virus subtype for Central African Republic, Democratic Republic of Congo and Gabon.