Influenza has for years ravaged domesticated chickens. Now scientists suggest that a small piece of duck DNA might protect the farm birds against the virus -- saving commercial flocks and lessening the possibility that humans could be exposed to dangerous strains of the disease.
In a study published online last month in Proceedings of the National Academy of Sciences, researchers said they had found that a key influenza-fighting gene in wild ducks is absent in chickens.
"If we could shut down influenza [in chickens], it would be of great commercial interest," said lead author Katharine E. Magor, a comparative immunologist at the University of Alberta in Edmonton, Canada.
All forms of influenza originate in ducks and other wild birds, which generally carry it with no ill effects, releasing it into the environment when they defecate.
Magor had been trying to understand why ducks had such an effective automatic response to influenza when she heard in passing at a conference that chickens lacked a gene called RIG-I.
This gene carries the code for a protein that immediately detects the RNA of the influenza virus after the virus invades the duck's lung and tracheal cells. It then sets off a chain reaction inside those cells to help fight off the disease.
"When we heard that chickens don't have this gene, we just about fell out of our chairs," Magor said.
Intrigued, she and colleagues from the University of Alberta and St. Jude Children's Research Hospital in Memphis, Tenn., searched for the RIG-I gene in chickens and failed to find it. They inserted the duck gene for RIG-I into embryonic chicken cells to see whether it made the cells immune to infection by influenza viruses.
The scientists infected the chicken cells with two strains: one run-of-the-mill H5N2 virus that lived in but did not harm wild ducks, and a deadly H5N1 strain isolated from a human fatality in Vietnam that was known on occasion to kill ducks as well.
"This strain . . . kills everything -- chickens in 18 hours, mice, humans -- but the virus didn't kill my ducks," Magor said.
The virus didn't kill the chicken cells containing the duck gene, either -- but it did kill normal chicken cells that lacked it.
Large-scale influenza outbreaks, such as the H5N1 virus that has plagued poultry farms around the globe since it was isolated from a farm goose in China's Guangdong province in 1996, pose threats to not only the industry and health of poultry workers. They also endanger the public because they increase the chances that a deadly strain that readily passes between humans could evolve.
"This study underscores the importance of this particular gene in fighting viral infections," said Adolfo Garcia-Sastre, a virologist at Mount Sinai School of Medicine in New York, who was not involved in the research.
Garcia-Sastre called the potential for creating a transgenic chicken immune to bird flu "a very attractive hypothesis," but he added that researchers would first have to test the gene in live chickens, not just chicken cells, to see whether the birds were immune to influenza and also ensure that they were healthy.