Scientists disarmed the Ebola virus by removing a single gene, providing a new laboratory tool that will help the development of drugs and vaccines against the lethal tropical disease.

Efforts to find ways of treating Ebola, a haemorrhagic fever that kills between 50-90 per cent of the people it infects, have so far been greatly held up by its extreme virulence. The extreme health hazard posed by the virus means that it can be studied only in highly specialised laboratories equipped to biosafety level four (BSL 4), the highest category of containment facility.

This is to protect researchers who handle it and to prevent accidental escapes, but it limits studies to about half a dozen laboratories worldwide and often makes research prohibitively expensive.

The new version of Ebola, developed by scientists at the University of Wisconsin-Madison, will allow the virus to be handled at lower levels of security, expanding the opportunities for research.

“We wanted to make biologically contained Ebola virus,” Yoshihiro Kawaoka, who led the study team, said. “This is a great system.”

In the study, which is published in the journal Proceedings of the National Academy of Sciences, the researchers inactivated one of Ebola’s eight genes. Without the gene, known as VP30, the virus cannot replicate itself and grow in human cells.

It can, however, grow in cells which have themselves been genetically modified to produce the viral protein that would normally be made by VP30. This means that it will be possible to study modified Ebola in these modified cells without any risk that a virulent virus might infect people.

“The altered virus does not grow in any normal cells,” Professor Kawaoka said. “We made cells that express the VP30 protein and the virus can grow in those cells because the missing protein is provided by the cell.

“This system can be used for drug screening and for vaccine production.”

Such studies are at present extremely difficult to run, because they are impractical in level-four facilities.

“This is an emerging virus and it’s highly lethal,” Professor Kawaoka said. “But because of the BSL 4 requirement, knowledge of this virus is limited.”

Ebola is thought to have first emerged in 1976 with outbreaks in Sudan and Zaire, and it has several strains. A new strain has recently emerged in Uganda, where it has killed at least 40 people.

The virus causes fever, diarrhoea and vomiting, and often also leads to heavy internal and external bleeding. It is highly infectious and is lethal in more than half of all cases. Treatments are available only to manage symptoms, and there is no human vaccine.

In a separate study published in the same journal, scientists at the US National Institute of Allergy and Infectious Diseases have found a new clue to a version of MRSA that is found in the community in parts of North America.

In Britain the superbug is generally confined to hospitals but in the US “community-associated” MRSA has been identified in settings such as gyms. The new study has isolated a particular strain that is responsible for most of these outbreaks.

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