Scientists have discovered clues about how the Ebola virus invades human cells, causing the severe fever and internal bleeding that kills 50–90 per cent of infected people.

They say the finding, published online on 12 July by Virus Research, could help researchers develop a vaccine or drug against the virus and its close relative, Marburg virus.

The team, led by Carolyn Wilson, of the US Drug Administration, identified two amino acids — the 'building blocks' of proteins — that the Zaire strain of the Ebola virus needs to enter cells.

When the researchers altered the virus's genetic material, so that different amino acids were produced, laboratory tests showed the virus was no longer able to infect human and monkey cells.

Altering either of the two amino acids, which form part of a protein on the surface of the virus, had the same effect.

"It is a well done study by highly reliable investigators," says James Cunningham, of Harvard Medical School in the United States. Last year he showed that a human enzyme helps Ebola fuse with the cells of people it infects (see Human enzyme helps Ebola virus invade cells).

He says the research could stimulate studies into questions such as why these two amino acids are important.

Javad Aman, of the US-based Army Medical Research Institute of Infectious Diseases, told SciDev.Net that it is interesting that a single amino acid mutation completely stops the virus in its tracks. "This would suggest that the virus may be, in fact, quite vulnerable."

Aman says that if future studies can determine the exact structure of the Ebola protein, this could help researchers design drugs.

"The study may also have implications for vaccine development if we can target the immune response toward these critical sites," he adds.

Reference: Virus Research doi:10.1016/j.virusres.2006.06.002