Scientists have produced genetically modified chickens that appear to prevent the spread of avian influenza. Though the chickens can themselves become infected with flu viruses such as H5N1, say the researchers, they cannot pass on the virus to any other birds with which they come into contact.
The technique, if adopted commercially, could provide a new strategy to slow or prevent outbreaks of bird flu within poultry flocks, which would protect the health of chickens and also reduce the chances of viruses transferring to humans. Many flu viruses that infect humans, including the H1N1 strain behind the swine flu pandemic that swept across the world in 2009 and caused 6,000 deaths, start in domestic birds before transferring to mammals such as horses and pigs, and then ending up in humans.
"Chickens … can enable new strains of flu to be transmitted to humans," said Laurence Tiley, a molecular virologist at the University of Cambridge's department of veterinary medicine, who led the work. "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."
The work is a proof-of-principle project and it would take several years of safety tests before any transgenic chickens would be allowed to enter the food chain.
Though there are no transgenic animals currently approved for human consumption, they might not be far away. Last year, the US Food and Drug Administration proposed allowing the sale of the AquAdvantage salmon – a modified North Atlantic salmon created by AquaBounty Technologies in Boston, Massachusetts. The company says the salmon grows at twice the speed of similar fish.
In the new research on chickens – described in the latest edition of Science – Tiley's team introduced a gene into chicken embryos that produces a small "decoy" molecule in the birds' cells. The decoy molecule mimics part of the molecular control mechanism of the bird flu virus, in this case H5N1. The virus incorporates the decoy instead of its own genetic material and becomes unable to replicate properly in the transgenic chicken's cells.
In their experiment, the scientists infected 10 genetically modified birds and 10 related, but non-GM birds with the avian H5N1 virus. Each infected group was then split into two sub-groups of five, and each sub-group was exposed to a new group of either 12 GM or 12 non-GM birds. The next step was to keep all groups for about 12 days and record the health status of all the birds.
All the non-GM birds died within five days of infection and the birds that came into contact with them also died a few days later, exactly as expected. The GM birds infected with H5N1 also died after a few days but, crucially, none of the birds they came into contact with – transgenic or not – became infected.
"Our genetic modification doesn't stop the birds getting flu if you infect them directly, but once they've got it, they don't transmit it," said Helen Sang of the Roslin Institute at the University of Edinburgh, who also worked on the project.
How the decoy prevents the spread of the virus is still uncertain. Tiley believes the virus that is produced and shed by the cells of the transgenic birds has a defect that prevents it from efficiently infecting other birds.
The genetic decoy would work against all strains of avian influenza, said Tiley, and the virus would be unlikely to evolve a way to escape its effects. "This is quite different from conventional flu vaccines, which need to be updated in the face of virus evolution as they tend only to protect against closely matching strains of virus and do not always prevent spread within a flock."
Whether or not transgenic chickens should be used commercially was a question for regulators, companies and consumers, the scientists said. "The genetic modification we describe is a significant first step along the path to developing chickens that are completely resistant to avian flu," said Tiley. "These particular birds are only intended for research purposes, not for consumption."
Even if they were approved for use, the technology would not be required everywhere. "The expectation is that you would introduce it in countries where there is endemic avian influenza," said Sang. "At the moment, in Europe it's not endemic so you wouldn't expect to use it here."
She added: "If you're thinking longer-term application of the technology, we want to facilitate public debate about using genetic modification for this purpose in commercial production birds."