THE long-term threat of an avian flu pandemic could be greatly reduced by a project to produce genetically modified chickens that can resist lethal strains of the virus.

British scientists are genetically engineering chickens to protect them against the H5N1 virus that has devastated poultry farms in the Far East, with a view to replacing stocks with birds that are not susceptible to influenza.

The technique should also offer protection against many other strains of flu with the potential to start a human pandemic, such as the H7 subgroup that was responsible for an outbreak in Dutch poultry in 2003.

If chicken populations were to be replaced with transgenic birds that were resistant to flu, it would remove a reservoir of the virus and make it much harder for it to spread to humans and trigger a pandemic.

The team, led by Laurence Tiley, Professor of Molecular Virology at Cambridge University, and Helen Sang, of the Roslin Institute, near Edinburgh, has already shown that chicken cells can be protected against flu by inserting small pieces of genetic material.

The researchers are now ready to begin a similar procedure with eggs and the first experiments are expected within weeks. Any breakthrough, however, will come too late to have an impact on the present outbreak of H5N1.

Even if the technique works, it will be several years before it can be used to stock farms and it also faces important regulatory hurdles and a battle to win over public opinion. If these obstacles are overcome and farmers are willing to adopt GM chickens, the entire world stock could be replaced fairly quickly.

“Once we have regulatory approval, we believe it will only take between four and five years to breed enough chickens to replace the entire world population,” Professor Tiley said. “Developing flu-resistant chickens has clear benefits for human health and animal welfare, as we wouldn’t have to slaughter chickens around the world. Chickens provide a link between the wild bird population, where avian influenza thrives, and humans, where new pandemic strains can emerge. Removing that bridge will dramatically reduce the risk posed by avian viruses.”

The research team is following three parallel approaches. One involves inserting a working copy of a gene that makes an antiviral protein called Mx, which is defective in many chicken breeds, and should improve their ability to fight off H5N1 and other strains.

The second approach is to harness a technique called RNA interference, in which small fragments of the genetic signalling chemical RNA are used to disrupt the workings of the flu virus.

By engineering chicken cells to make small RNA molecules that confuse the flu virus, the scientists hope to confer resistance to a wide variety of strains. The third strategy is similar to the second, but involves using RNA molecules as decoys, which trick the flu virus into copying them rather than itself. All three could potentially be incorporated in the same GM chickens.

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