Scientists in China report that they have identified the gene which determines the virulence of the H5N1, or bird flu, virus in poultry. The breakthrough could pave the way for new vaccines, the scientists claim.

Some strains of H5N1 kill more than half those they infect, while others leave virtually all their victims standing. Understanding what it is that makes one strain of the virus more deadly than another gives researchers something to target when developing a vaccine.

He says that a vaccine targeting the "highly pathogenic" NS1 gene could be developed very quickly. "Technically, that can happen very soon, but it is the tests and other procedures that will take a long time," he said.

The research team took samples from geese that died from the disease in 1996, in the southern Guangdon province, and studied two closely related strains of the virus. One strain was very deadly to chickens, and the other relatively harmless. They found that the key differences lay in just four genes.

By genetically altering the virus to create four new variations, they were able to determine which of those genes controlled how likely the virus is to kill anything it infects.

The work is published in the November issue of the Journal of Virology. ®

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