British scientists have developed genetically modified (GM) chickens that cannot transmit bird flu infections –a step that in future could reduce the risk of avian flu spreading and causing deadly epidemics in humans.
Scientists from Cambridge and Edinburgh universities said that while the transgenic chickens still got sick and died when they were exposed to H5N1 bird flu, they didn't transmit the virus to other chickens.
"Preventing virus transmission in chickens should reduce the economic impact of the disease and reduce the risk posed to people," said Laurence Tiley, of Cambridge's department of veterinary medicine, one of the lead researchers on the study.
H5N1 bird flu has been circulating in Asia and the Middle East, with occasional outbreaks in Europe, since 2003 and has killed or forced the destruction of hundreds of millions of birds, according to the world animal health organisation OIE.
306 people dead
It rarely infects people but when it does it is deadly: the World Health Organization has documented 516 cases in people since 2003 and the virus has killed 306 of them.
Experts say the danger is that the virus will evolve into a form that people can easily catch and pass to one another, causing the transmission rate to soar and producing a pandemic in which millions of people could die.
In Southeast Asia, China and parts of Africa, bird flu is already a major economic and food security issue, and also poses a constant threat of being transmitted to humans.
South Korea, already battling an outbreak of foot-and-mouth disease, said this week it was raising its bird flu alert level after detecting H5N1 bird flu at poultry farms.
Increasing food security
Helen Sang from the Roslin Institute at Edinburgh University, who worked with Tiley, told a joint briefing the GM chickens could offer a way to improve economic and food security in parts of the world where bird flu is a major threat, but said using them would probably add slightly to farming costs.
"Countries like China are interested in the possibility of genetic modification to protect their poultry stocks and people," she said. "It will inevitably be more expensive because you'd have to use the products of breeding companies to stock the producers." At the same time, the need for vaccination and losses from whole flocks being infected should be reduced.
While large poultry producers could benefit from this early type of transgenic bird, smaller "backyard" farmers would need to wait until scientists create birds that can be bred on small farms. "That would be a means of ensuring that the birds these small farmers bred themselves still carried the protective transgene," Tiley said.
To breed their GM chickens, the researchers introduced a new gene into them that manufactures a small "decoy" molecule that mimics an important control element of the bird flu virus.
The replication machinery of the virus is tricked into recognising the decoy molecule instead of the viral genes and this interferes with the virus's replication cycle.
After producing the modified chickens, they infected 10 of them and 10 normal chickens with H5N1 bird flu. Like the normal chickens, the transgenic birds became sick with the virus, but they did not transmit the infection to other chickens kept in the same pen with them - even if those chickens were normal, non-transgenic birds. The study was published online in Science.
The researchers said they now plan to work on trying to make chickens that are fully resistant to bird flu rather than just blocking bird-to-bird transmission.
(Reuters Health, Kate Kelland, January 2011)
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