The world may soon forget about COVID-19, but there are signs that the next pandemic - avian flu - is already brewing. Scientists have now shown that genetically engineering chickens can reduce their chances of contracting and spreading disease, but it's not foolproof.
Bird flu is a difficult disease to control. It has strong adaptability and high transmissibility, and can spread over long distances due to the free migration of migratory birds. Large-scale raising of chickens and eggs will speed up the spread and mutation of the virus. Once the virus spreads among people, farmers and authorities often have to cull millions of birds to curb the spread of the virus.
In the new study, British scientists investigated the feasibility of genetically engineering chickens to become more resistant to avian influenza. Previous research had shown that a protein called ANP32A is often targeted by viruses for replication, so the team altered the gene that produces this protein.
The gene-edited chickens were then exposed to normal doses of the H9N2-UDL strain through close contact with infected birds. It was found that 90% of the genetically modified chickens were able to resist viral infection and would not be transmitted to other chickens. Their health and growth were not adversely affected in any way.
Next, the team tested higher doses of the virus - 1,000 times higher than would be expected in natural exposure. In this case, 50% of the chickens were infected, although virus levels in vaccinated chickens were still much lower than in unvaccinated chickens. Even at higher doses, the gene editing reduced the onward spread of the virus, with only one of the four unedited chickens becoming infected, and no gene-edited chickens that were housed with the infected edited chickens became infected.
However, simply editing a gene may not be enough. The study found that the virus can bypass the deleted ANP32A gene and can still use the related proteins ANP32B and ANP32E to replicate, which proves the frustrating ability of the virus to evolve rapidly. Follow-up tests in lab-grown chicken cells showed that knocking out all three genes successfully prevented the virus from growing, but unfortunately, the combination was expected to affect the health of the chickens.
While this gene-editing approach may bring some benefits - even if they are limited to safeguarding the global supply of chicken nuggets - other scientists say it won't be enough to significantly curb bird flu.
Professor Raina MacIntyre, an expert on influenza and emerging infectious diseases at the University of New South Wales, said: "If chickens can be engineered to be resistant to avian influenza viruses, it may be possible to reduce the risk of avian influenza viruses causing a human pandemic. However, avian influenza spreads globally not only through the poultry trade, but also through wild animals such as ducks and geese. Avian transmission. These birds also spread avian influenza as they migrate between countries and continents, independent of farmed poultry. So the engineering of farmed chickens alone is not enough. Another major problem is that influenza A viruses are highly mutable and the antigens are constantly drifting. This means that the virus itself is likely to evolve to overcome the engineered traits of the birds."
The researchers said further work will continue to help chickens resist bird flu.
The research was published in the journal Nature Communications.