Diseases such as avian flu trigger the culling of millions of birds each year. But that need not be the case for much longer.

Vaccines are one preventive strategy employed in some countries, but they do not stop birds from being infected, getting mild versions of the disease and transmitting it to healthy chickens. In fact, this imperfect shield can make things worse, incentivising the virus to mutate to evade the vaccine.

And an even more grim possibility is that the viruses that afflict domestic birds can spill over into humans with deadly effect.

So scientists are working on a more permanent solution: gene editing, which is designed to alter specific genes in an organism to enhance certain characteristics or inhibit others. It is sometimes lumped into the same category as genetic modification, which involves the transfer of a gene from one organism to another.

Genetically modified organisms are strictly regulated in the EU, due to longstanding fears of unintended environmental and public health effects. Some campaign groups say gene editing brings similar risks.

The use of gene editing techniques “could not only exacerbate the negative effects of industrial farming on nature, animals and people, but it could effectively turn both nature and ourselves (through the food we eat) into a gigantic genetic engineering experiment with unknown, potentially irrevocable outcomes”, Greenpeace said in a statement earlier this year.

Proponents, meanwhile, assert that gene editing technology is merely a more precise version of the traditional selective breeding of animals.

At the heart of the gene editing solution is the Crispr tool, which is designed to work like a pair of genetic scissors. This tool could be used, for instance, to edit out a section of chicken DNA to prevent the bird flu virus from taking hold in the cells and replicating.

Prof Helen Sang, a geneticist at the Roslin Institute at the University of Edinburgh, is part of a team of scientists that is working on the early stages of such a project. Crispr technology is efficient because it allows for the evaluation of the edit in lab-grown cells – if those results look encouraging, it can then be tested in birds, she says.

Pretty much everything we eat has been selectively bred – from crops to poultry. But in many places, genetically modified crops are common. In the US, for instance, most soy and corn are engineered to maximise output. In 2015, US regulators also granted the first approval of an animal (an Atlantic salmon) whose DNA had been scientifically modified for human consumption. Disease-resistant pigs are expected to be next in line.

Selective breeding fundamentally alters the genetics of an organism but is perceived as natural, while using genetic editing technology for the same goal is considered unnatural, noted Dr Laurence Tiley, a molecular virologist at the University of Cambridge’s department of veterinary medicine.

Tiley’s and Sang’s research, about a decade ago, yielded early success in genetically modifying chickens to prevent the spread of bird flu. But they didn’t pursue the project after realising the technology wasn’t robust enough to completely prevent the birds from getting the flu in the first place.

In the years since, Crispr technology has grown from relative obscurity to revolutionising the fields of biomedical research, clinical medicine and agriculture.

Clearly, these gene editing tools are not the way nature intended, but are very precise, says Tiley. “You can make exactly the change you want in exactly the appropriate place. And you can check it … and confirm that there’s nothing else that you’ve made any other changes to.”

Earlier this year, a consultation by the UK government opened the door for gene editing of crops and livestock in England. The changes to the current strict rules – which originate from the EU and make gene editing for crops and livestock almost impossible – are intended to bring widespread benefits to consumers and farmers, including healthier food, lower antibiotic use and better animal welfare.

But campaigners say loosening the rules could instead be worse for animal welfare, for instance, if the technology was used to promote growth over animal health, or to enable livestock to be kept in crowded conditions.

It’s not an either/or situation, says Tiley, adding: “I think there is an obvious case to improve livestock production … to reduce the transmission of infectious diseases. But there are some things that, no matter how hard you try, you’re going to have a disease problem, and if you can genetically engineer these problems away, then that’s a good thing to do.”

In wealthy countries, chicken consumption has grown by 70% since 1990 and continues to grow, with 65 billion chickens consumed globally each year. Until an alternative protein kicks in as the default solution, then the traditional way of consuming protein needs to be improved, says Yehuda Elram, head of the Israeli startup EggXYt, which is working on gene-editing tools to tweak DNA fragments in chickens to attack viruses that cause avian flu.

“With Covid, the world is becoming more familiar with what science can do to solve very challenging problems. We’re trying to do our bit to improve the way chickens are produced, to elevate animal welfare,” says Elram.

It is not as easy to confer disease resistance via gene editing to pigs, primarily due to the very different physiology of the avian egg compared with mammals. The technology also needs to be refined to be made less laborious, says Jiri Hejnar at the Czech Academy of Sciences.

Hejnar’s laboratory published encouraging proof of concept data early in 2020 describing the use of Crispr to make chickens resistant to the avian leukosis virus (ALV), which can lead to symptoms such as weakness, diarrhoea and the formation of tumours in poultry. But the project has been abandoned due to a lack of commercial interest, he said.

Even as the science marches on, the commercial case for any such progress is handicapped by the lack of a global regulatory consensus and consumer acceptance, the scientists said.

We have the tools required to develop disease-resistant chickens, but it’s important to bring the public along with the journey, says Tiley. “If somebody jumps into a room and shouts fire, people tend to respond. And so, if somebody says GM food is dangerous, people tend to take that at face value,” he says.

But, the experience of Covid has perhaps impressed upon people that pandemics can be very bad, he says: “If you pick your species carefully, and your objectives, in a way that is readily justifiable, say avian flu in chickens, there are multiple arguments that you can make that are quite persuasive.”

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