21st June 2018

Gene-edited pigs made resistant to billion dollar virus

Scientists at the University of Edinburgh report that gene-edited pigs have been made resistant to porcine reproductive and respiratory syndrome (PRRS) – one of the world's most costly animal diseases.

Tests with PRRS ‒ also known as "blue-ear" ‒ found the pigs do not become infected at all. The animals show no signs that the change in their DNA has had any other impact on their health or wellbeing.

The virus causes breathing problems and deaths in young animals and if pregnant sows become infected, it can cause them to lose their litter. PRRS is endemic in most pig producing countries worldwide. Vaccines have mostly failed to stop its spread – and the virus continues to evolve rapidly, costing the pig industry around $2.5 billion (£1.75bn) each year in lost revenue in the US and Europe alone.

The virus infects pigs using a receptor on their cells' surface called CD163. Researchers at the Roslin Institute (part of the University of Edinburgh, Scotland) used gene editing techniques to remove a small section of this gene. They focused on the section of the receptor that the virus attaches to, leaving the rest of the molecule intact.

The team collaborated with Genus PLC, a global animal genetics company, to produce pigs with the specific DNA change. Previous studies had shown that cells taken from these animals were resistant to the virus in laboratory tests – but this was the first time the researchers have exposed whole, live pigs to the virus to see if they are infected. None of the animals became ill when exposed to the virus, with blood tests finding no trace of the infection.

Other groups have used gene editing to create PRRS-resistant pigs by removing the whole CD163 receptor. However, removing only a section of CD163 allows the receptor to retain its ordinary function in the body and reduces the risk of side effects, the researchers say.

"These results are exciting, but it will likely be several years before we're eating bacon sandwiches from PRRS-resistant pigs," said Dr Christine Tait-Burkard from the Roslin Institute. "First and foremost, we need broader public discussion on the acceptability of gene-edited meat entering our food chain, to help inform political leaders on how these techniques should be regulated. We also need to carry out longer-term studies to confirm that these genetic changes do not have any unforeseen adverse effects on the animals. If these studies are successful and the public are accepting of this technology, we would then be looking to work with pig breeding companies to integrate these gene edits into commercial breeding stocks."

Genetically modified animals are banned from the food chain in Europe. It is not clear what regulations would apply to gene-edited animals, however, since the approach is different. GM techniques are controversial because they can involve introducing genes from another species into an animal. In contrast, gene editing speeds up processes that could occur naturally through breeding over many generations, without introducing foreign genes.

"Gene editing gives us a powerful tool to help reduce losses in the farming industry, while improving the health and welfare of the animals themselves," said Professor Alan Archibald, also from the Roslin Institute.

"These results are very exciting and further underscore the potential, through gene editing, to provide incredible benefits to the global pork industry, and society as a whole, by improving animal health," said Jonathan Lightner, Chief Scientific Officer at Genus PLC. "We look forward to further collaboration with the University on this exciting project."

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