British scientists produce PRRS-resistant pig

Pigs do not become infected with porcine reproductive and respiratory syndrome when part of their DNA is removed

A new study by scientists in Scotland has produced a pig resistant to a costly disease by tinkering with the animal’s DNA.

Research carried out at the Roslin Institute, which is part of the College of Medicine and Veterinary Medicine at the University of Edinburgh, found pigs do not become infected with porcine reproductive and respiratory syndrome (PRRS) when researchers removed part of their DNA.

What’s more, the animals showed no signs that the change in their DNA has had any other impact on their health.

PRRS is endemic in most pig-producing countries and causes breathing problems and deaths in young animals. If pregnant sows become infected with the virus, it can cause them to lose their litter.

Vaccines have mostly failed to stop the spread of the virus, which continues to evolve rapidly, costing the pig industry about $3.3 billion each year in lost revenue in the U.S. and Europe alone.

The virus infects pigs using a receptor on their cells’ surface called CD163. Researchers at the Roslin Institute used gene-editing techniques to remove a small section of the CD163 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 from these animals were resistant to the virus in laboratory tests, but this is the first time researchers have exposed these pigs to the virus to see if they become infected.

They found that none of the animals became ill when exposed to the virus, and blood tests found 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.

Dr. Christine Tait-Burkard from the Roslin Institute said commercial use is still some years off.

“These results are exciting but it will still likely be several years before we’re eating bacon sandwiches from PRRS-resistant pigs.

“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.

She also said longer-term studies are needed.

Genetically modified animals are banned from the food chain in Europe but it remains unclear what regulations would apply to gene-edited animals.

GM techniques have been controversial because they can involve introducing genes of other species into an animal. In contrast, gene editing speeds up processes that could occur naturally through breeding over many generations, without introducing foreign genes.

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