Genetically modified chickens don't pass on the flu

January 19, 2011

Richard Knox

Here's a neat genetic trick: Make a chicken that can get the flu, but can't pass it on to other birds -- or, presumably, to the humans who take care of them.

British researchers have done it.

The British team, with the support of a big poultry breeder and government funding, inserted a gene into chickens that blocks flu viruses from replicating. These genetically modified chickens can get infected. But their cells don't spew forth zillions of copies of flu viruses -- so nearby poultry don't get sick.

Their achievement, reported in the current issue of Science, addresses major problems for both poultry breeders and public health officials who worry about chickens as sources of flu viruses that make humans sick.

Chickens and other domestic fowl often serve as bridges for new flu viruses that pop up in wild birds and later cause human outbreaks. Most of the 517 reported cases of deadly H5N1 bird flu have been in people who've had contact with domestic poultry.

There are flu vaccines for chickens. But, like human vaccines, they have to be updated continually as new flu mutants evolve. Also, they don't totally prevent flu infections in poultry -- they just suppress them. So vaccinated flocks can still have "silent" outbreaks that don't kill off birds but allow the virus to mutate undetected.

The secret of flu-proofing chicken flocks is an artificial gene that contains a snippet of genetic material from the H5N1 flu virus. This bit of RNA codes for polymerase, an enzyme flu viruses need to make more of themselves.

The cells of GM chickens make this fake polymerase. When scientists infected the modified birds with lethal doses of H5N1, the virus latched onto the decoy form of polymerase. These viruses couldn't replicate and spread to other chickens through the birds' exhalations and droppings.

This is better than a vaccine, the researchers say, because the virus probably won't be able to evade the genetic defense as it can vaccines. That's because each one of the flu virus's eight genetic elements needs a polymerase gene to replicate; simultaneous mutants in all these places on the viral genome is "highly improbable," the scientists say.

Another big advantage: No flu virus of the important "A" family that includes H5N1, H1N1 and H3N2 -- the main threats to human health -- should be able to circumvent the genetic defense because they all need the same form of polymerase to replicate.

Intriguing as the new approach is, the problem is far from solved. Years more testing will be needed to make sure there's no hidden hazard from this type of genetic modification. And then there's the public relations work that will be needed to persuade government agencies and consumers to accept the GM chickens.

If these hurdles can be overcome, it might not be such a daunting task to replace the billions of ordinary chickens in commercial poultry herds with the GM type.

"That's because the trade in both broiler and egg-laying chickens has become consolidated in a handful of companies," Michael Greger of the Humane Society of the United States told Martin Enserink of Science.

As for the millions of backyard and rooftop flocks in developing countries around the world, Greger says the strategy would be provide their owners with GM chickens they can breed themselves. The flu-proofing gene would get passed along to their offspring.

The next horizon: GM pigs, ducks, turkeys and quail. They all get the flu, too. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.