H5N1: Chickens engineered to be bird flu decoys

Scientists have engineered chickens that block the spread of avian influenza viruses.

These chickens – which are not intended for human consumption – still got the flu and died, but they didn’t pass the virus on to the healthy chickens they lived with.

These genetically modified chickens (pictured) could one day thwart outbreaks of a global threat to poultry production and human health that has caused the destruction of hundreds of millions of birds and the death of 306 people. But whether these chickens will be safe to eat is yet to be determined.

“Chickens are potential bridging hosts that can enable new strains of flu to be transmitted to humans,” says lead investigator Laurence Tiley of University of Cambridge. “Preventing virus transmission in chickens should reduce the economic impact of the disease and reduce the risk posed to people exposed to the infected birds.”

In this new study, chicken cells produced an RNA ‘decoy’ that resembles the viral genome. It binds to an important part of the virus, preventing its spread.

In particular, the researchers introduced a new gene into these chickens that produces a small molecule that mimics a vital enzyme of the H5N1 flu virus. The decoy tricks the virus’s production machinery into recognizing the decoy instead of the virus’s genome. This makes the enzyme useless, interfering with the replication of the virus.

And none of their cagemates – engineered or not – caught the flu. That means that only one or a few chickens would become infected if the virus entered a flock.

This strategy of developing chickens genetically resistant to infection has advantages over vaccinating the birds. Vaccination, the authors say, still allows the virus to circulate undetected through flocks of chickens, possibly mutating and developing resistance.

It costs approximately $79,000 to produce “a small number of stable transgenic birds you can characterize and breed from,” says study author Helen Sang of University of Edinburgh.

A truly disease-resistant bird wouldn’t be available any time soon, but the chicken method could help develop flu-fighting pigs, ducks, quail and turkeys.

Science reports:

Transgenic chickens could theoretically replace nontransgenic breeds worldwide in a few years, says Michael Greger, director of Public Health and Animal Agriculture at the Humane Society of the US. That’s because the trade in both broiler and egglaying chickens has become consolidated in a handful of companies, which essentially determine what stocks are used by chicken farmers worldwide.

It would inevitably be more expensive, not to mention that these companies don’t sell to the vast number of people in the developing world who have a small flock in their backyard or on their rooftop – and that’s where avian influenza has been the most difficult to control [Science].

The study was published in Science last week and was partly funded by Cobb-Vantress, a major international chicken-breeding company.

Image by Norrie Russell, courtesy of Valerie White and The Roslin Institute