The world may be quickly forgetting about COVID-19, but there are signs the next pandemic is already cooking up – bird flu. Scientists have now demonstrated that genetically engineering chickens can reduce their chances of catching and spreading the disease, but it’s not foolproof.
Avian influenza, or bird flu, is a tricky disease to control. It’s adaptable and highly transmissible, and can be spread long distances thanks to the freedom of movement migratory birds enjoy. Large-scale farming of chickens for meat and eggs accelerates the spread and mutation rate of the virus, and once it’s in a population farmers and authorities often have to resort to culling birds by the millions to try to curb it.
For the new study, scientists in the UK investigated how practical it might be to genetically engineer chickens to be more resistant to bird flu. Previous studies have shown that a protein called ANP32A is usually the target for the virus to replicate, so the team altered the gene that produces this protein.
The gene-edited chickens were then exposed to a normal dose of the H9N2-UDL strain of the virus through close contact with infected birds. And sure enough, 90% of the engineered birds resisted infection, and didn’t spread it to other chickens. No adverse effects to their health or growth was detected.
Next, the team tested a much higher dose of the virus – 1,000 times that of natural exposure. In this case, 50% of the chickens were infected, although the levels of the virus in the inoculated birds remained much lower than in non-edited chickens. Even against the higher doses, the gene edits reduced the onward spread of the virus, infecting just one of four non-edited chickens and no gene-edited birds that shared an enclosure with the infected, edited chickens.
Editing a single gene may not be enough, however. Testament to the virus’ frustrating ability to evolve quickly, it was found that it could bypass the deleted ANP32A gene and still replicate using related proteins ANP32B and ANP32E. Follow-up tests in lab-grown chicken cells showed that knocking out all three genes successfully blocked growth of the virus, but unfortunately this combo is expected to affect the health of chickens.
While this gene-editing approach may have some benefits – even if they’re limited to safeguarding the world’s supply of chicken nuggets – other scientists say it isn’t enough to curb bird flu significantly.
“If chickens could be engineered to be resistant to avian influenza viruses, that may reduce the risk of the emergence of a human pandemic virus from avian influenza,” said Professor Raina MacIntyre, an expert in influenza and emerging infectious diseases at the University of NSW. “However, avian influenza spreads globally not just through poultry trading, but also through wild waterfowl such as ducks and geese. These birds can spread avian influenza as they migrate across flyways between countries and continents, independent of farmed poultry. So, engineering farmed chickens alone is not enough.
“The other main concern is influenza A viruses are highly mutable and subject to continual antigenic drift. This means the virus itself will likely evolve to overcome engineered traits in the birds.”
The researchers say that further work will continue to help shore up the chicken population against bird flu.
The research was published in the journal Nature Communications.
Sources: University of Edinburgh, Scimex
