January 14, 2011

New transgenic chickens engineered to prevent spread of bird flu

A new type of chicken has been engineered to possibly help prevent the spread of bird flu - a worrisome virus which already caused extensive economic harm on farms, especially in Asia.

Several farmers have gone to great lengths to prevent a poultry-based pandemic, but the newest results are "a significant first step along the path to developing chickens that are completely resistant to avian flu," said Lawrence Tiley, a molecular virologist from the University of Cambridge's Department of Veterinary Medicine.

Usually kept in close quarters, chicken flocks are prone to rapid spread of viruses. The new study, published online on January 13 in Science, describes a genetic trait that seems to prevent chickens from infecting their feathered neighbours, which could also reduce the risk that the flu would jump to humans, as has occurred with sporadic cases of H5N1 since 1997.

The gene makes "an innocuous decoy RNA" that closely resembles the viral genome. This decoy molecule tricks the virus into replicating it instead of producing more viral material. Incorporating the gene that makes this molecule into poultry, the research team found that although birds can still be infected, and even die from the flu, they do not pass it on to nearby non-transgenic chickens.

"The decoy mimics an essential part of the flu virus genome that is identical for all strains of influenza A," said Tiley, who co-authored the new study. The RNA that the gene generates is so general that it should work against all forms of the flu year after year, rather than needing to be reconfigured like the influenza vaccines currently administered to chicken flocks, the researchers concluded.

Crops that are genetically modified (GM) can boost yield, increase nutritional value and stave off disease, but they have been met with opposition from numerous corners. Researchers themselves continue to learn more about how these introduced genes play out in the broader environment over time. Although limited in some parts of the globe, GM crops are widespread in the US, and one 2010 report showed that transgenic crops were expanding to grow beyond their tended fields.

How this technology and its regulation will play out on the animal side of agriculture remains to be seen. The US Food and Drug Administration has been reviewing the case for GM salmon that grow more quickly than typically farmed Atlantic salmon. And the researchers behind the new study suggested that the chicken strategy might be replicable in pigs.

Some proponents of GM animal research play up the public health angle. "Infectious diseases of livestock represent a significant threat to global food security and the potential of pathogens, such as bird flu, to jump to humans and become pandemic has been identified by the government as a top-level national security risk," said Douglas Kell, chief executive of the UK's Biotechnology and Biological Sciences Research Council, which backed the study.

The researchers also noted in their paper that unlike a vaccine, this genetic tactic is unlikely to prompt resistance in bird flu because overcoming the gene's decoy RNA would necessitate substantial changes in all of the virus's eight genome segments, which, they concluded, is "a statistically highly improbable event."

But meat from these GM birds is unlikely to show up in chicken nuggets any time soon. "These particular birds are only intended for research purposes, not for consumption," Tiley said.