Gene editing also helped curb the spread of the virus. Four ordinary chickens were placed in the same incubator with the genetically modified birds, which had already been exposed to high levels of the virus. Of the four, only one became infected.
Researchers monitored the genetically modified birds over a two-year period and found that the genetic changes had no negative effects on their health or egg production.
“This demonstrates a possible mechanism for reducing chicken susceptibility to avian influenza,” says Carol Cardona, a veterinarian and professor of avian health at the University of Minnesota College of Veterinary Medicine, who was not involved in the study. “But even if we protected every single chicken in the world, the flu wouldn’t go anywhere.” Bird flu has been detected in more than 100 different bird species.
The fact that there have been some breakthrough infections means the virus still has a chance of infecting other birds and could “escape” the effects of the vaccine by mutating and no longer using the ANP32A protein to reproduce. When the British researchers took samples of the virus from infected genetically modified chickens, they actually found some mutations in the part of the virus that this protein interacts with. “There is an opportunity for this virus to adapt and change,” says Cardona.
During the press conference, Barclay said these virus mutations did not make the chickens sicker. The team also wanted to ensure that these changes wouldn’t cause more severe infections in humans, so they added the mutated viruses to human respiratory cells that had been cultured in a dish. They found that the mutations do not cause the virus to multiply in a way that would pose an increased risk to people.
It is also not known how the genetically modified chickens will perform against the much more aggressive strains of bird flu, such as H5N1, which were not tested in the study. Barclay said they chose H9N2, which is considered a low pathogenicity virus that causes little or no evidence of disease, in part because it is more common. In addition, the deliberate infection of chickens with H5N1 raises animal welfare concerns as it causes serious illness and is often fatal.
The authors identified two other related proteins, ANP32B and ANP32E, which they believe would prevent virus replication. In chicken cells grown in the lab, they changed the genes that code for all three proteins and exposed them to the flu virus. The changes successfully blocked the growth of the virus in the cells, but researchers have not yet bred chickens with all three changes.