Scientists have successfully altered the genes in pigs in order to defend them against one of the costliest viral infections affecting commercial breed stocks in modern history.
Porcine Reproductive and Respiratory Syndrome (PRRS) is a viral infection that induces reproductive failure in breeding animals and respiratory disease in pigs of any age. Because it evolves rapidly, PRRS is a costly disease totaling $2.5 billion in lost revenue every year in the US and Europe alone. Past attempts at vaccinations have failed to stop its spread, but researchers now believe editing genetic codes of swine could severely halt the spread of the virus.
The technique uses CRISPR and works by targeting certain genes responsible for certain traits. Enzymes produced by CRISPR called Cas9 bind to DNA, cut it, and shut it off. The PRRS virus infects pigs' cell receptor – a protein molecule that receives chemical signals from outside a cell – called CD163. In the study, scientists were able to use gene-editing techniques to remove a section of this gene. Because they focus on the one receptor that the virus attaches to, the rest of the molecule is left intact. According to researchers, edited pigs showed no signs of adverse health effects or any impact on their DNA. Researchers say other scientists have used gene-editing techniques to remove the entire CD163 receptor, but the new method of removing just a portion allows the receptor to stay in the body, retaining its ordinary function and reducing the risk of side effects.
The study is published in the Journal of Virology.
Researchers teamed up with a leading global animal genetics company to produce pigs with this DNA change and exposed them to the virus to see if they would become infected. None of the animals became sick after exposure to the virus and blood tests “showed no trace” of the infection.
This same technique has been used to make highly malaria-resistant mosquitoes and has been approved by the US Food and Drug Administration to modify plant foods. Genetically-modified animals for consumption are currently banned in Europe, but there is no legislation regarding gene-edited animals.
Despite its potential, the scientists say it’s just a step in the direction of gene-edited animals.
"These results are exciting but it will still likely be several years before we're eating bacon sandwiches from PRRS-resistant pigs,” said Dr Christine Tait-Burkard in a statement. "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.”
Tait-Burkard says more longer term studies are needed to determine any other unforeseen adverse effects before moving forward with gene-edited commercial breeding stocks.