Scientists have genetically engineered pigs to be immune to one of the world’s most costly animal diseases, in an advance that could propel gene-editing technology into commercial farms within five years. The trial, led by the University of Edinburgh’s Roslin Institute, showed that the pigs were completely immune to porcine reproductive and respiratory syndrome (PRRS), a disease that is endemic across the globe and costs the European pig industry nearly £1.5bn in pig deaths and decreased productivity each year. Pigs infected with PRRS are safe to eat but the virus causes the animals breathing problems, causes deaths in piglets and can cause pregnant sows to lose their litter. There is no effective cure or vaccine, and despite extensive biosecurity measures about 30% of pigs in England are thought to be infected at any given time. After deleting a small section of DNA that leaves pigs vulnerable to the disease, the animals showed no symptoms or trace of infection when intentionally exposed to the virus and when housed for an extended period with infected siblings. “It is what we call complete immunity,” said Christine Tait-Burkard of the Roslin Institute and first author of the work, published in the Journal of Virology. The advance could have huge animal welfare and economic benefits to farming, she said, but added it is “likely to be several years before we’re eating bacon sandwiches from PRRS-resistant pigs”. Genetically modified animals are banned from the food chain in the UK and throughout Europe but it is not clear whether these regulations would apply to gene-edited animals, since the technology and resultant genetic changes are different. It also remains to be seen whether the public will embrace the prospect of genetically edited meat. Gene editing differs from older genetic modification techniques, which often involve transferring genes from one species to another. By contrast, gene editing uses precise molecular tools to remove small stretches of DNA or alter single letters in the genetic code – effectively speeding up processes that could occur naturally over many generations. The PRRS-resistant pigs were made by removing about 450 letters of DNA, causing a receptor, called CD163, that sits on the outside of pig cells to be made lacking one tiny, precise segment that the virus binds to. This means the virus bounces off the cell rather than entering it and multiplying. “The resulting pig is still 100% pig … or 99.9999999% of a pig,” said Tait-Burkard. “It’s not something new that people should be afraid about.” In the trial, the animals showed no signs that the change in their DNA had any other impact on their health, fertility or wellbeing. The work was funded by Genus Pic (Pig Improvement Company), whose nine pedigree herds sire about 30% of the world’s commercially farmed pigs. The company is now conducting further tests ahead of plans to introduce the edit commercially, starting in the US. Jonathan Lightner, chief scientific officer for Genus, said: “We know that farmers are enthusiastic about it and that’s because they’ve seen what this disease does on their farms.” He added: “We’re doing [further] development in the US because the regulatory framework is clearer there … and public acceptance we imagine will be more difficult in the EU than in North America.” PRRS is endemic across the world. There is no treatment, and vaccines are ineffective. A 2011 study conducted by the Royal Veterinary College found that in England 30% of the pig population had the virus, and the figure was higher in areas with dense pig populations. While there is no current treatment for the virus, one of its effects is to hamper the immune system, leaving pigs at risk of picking up secondary infections. So antibiotics are typically used as a blanket treatment for pigs when farms are infected. Georgina Crayford, a senior policy adviser at the National Pig Association, said immunity to the disease could help tackle excess antibiotic use on farms. “We’ve halved the antibiotic use in the pig industry in the last two years, which is really fantastic, but PRRS in the future is going to hamper any further significant progress,” she said. PRRS is just one of several animal diseases being targeted through gene editing. Separately, scientists at Roslin are attempting to engineer resistance to African swine fever, a highly infectious disease that is sweeping through the Baltic states and into Europe. Others are focused on avian flu, E coli, campylobacter and various fish diseases. Darren Griffin, professor of genetics at the University of Kent, said: “There is a still a way to go in terms of efficacy and safety testing ... but the results of this study provide encouragement and hard evidence for an approach that could be applied in the future. “In general terms there is still public concern about gene editing in the food that we consume, but this needs to be countered by hard evidence from well-designed studies. Alarmist titles such as ‘Frankenstein foods’ should play no part in the discussion.” Listen to Hannah Devlin discuss this issue with Crayford and Roslin’s Prof Alan Archibald on the Guardian’s Science Weekly podcast here.
Scientists at the University of Edinburgh’s Roslin Institute have genetically engineered pigs to be completely immune to porcine reproductive and respiratory syndrome (PRRS), a virus that costs the European pig industry almost £1.5bn a year. The achievement offers significant potential animal welfare and economic benefits for farmers. Following further tests, gene editing could be introduced to commercial farms within each year.