SEPTEMBER 2018 • COUNTRY LIFE IN BC Genetic editing stops deadly virus in pigs


Great news for producers but will consumers buy in? Among the challenges hog


producers face is protecting their pigs from illness and disease. One of the world’s costliest diseases endemic in


Research by MARGARET EVANS


all pork-producing countries is Porcine Reproductive and Respiratory Syndrome (PRRS), a viral disease that can cause reproductive failure (abortions, infertility or weak or stillborn piglets) in sows and respiratory tract illness including pneumonia in young pigs. The problem affects the swine industry worldwide with serious economic consequences. In the US and Europe, costs to the industry are estimated at $2.5 billion each year. The virus was first identified in the late 1980s and no pigs are naturally resistant to it. In Canada, a vaccine is


available for young pigs that might be at risk for exposure to the virus. But at the University of Edinburgh’s Roslin Institute in Scotland, scientists have produced pigs that can resist PRRS by a change in their genetic code. The pigs are, in effect,


gene-edited. PRRS infects pigs by using


a receptor on the pig’s cells’ surface called CD163. The scientists focused on a specific section of the receptor that the virus attaches to, then removed that section leaving the rest of the molecule intact. When they


tested those pigs by exposing them to the virus, the pigs did not become infected and they did not show any sign that the change in their DNA affected their health or well- being. It all came about after 20


years of research led to identifying a lock-key interaction by which the virus can enter the pig’s cells and multiply.


“Basically, the virus brings


the key in the form of proteins on its surface and interacts with a lock, which is on the target cells that the virus infects, a protein called CD163,” says Dr. Christine Tait- Burkard, assistant professor at Roslin Institute. “This protein looks like nine pearls on a string. Only pearl number five actually interacts with the virus and serves the lock-key mechanism. That sparked the idea to simply remove that pearl, or domain five, to stop the lock-key interaction of the


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Christine Tait-Burkard pictured with gene-edited pigs resistant to one of the world’s most costly animal diseases, PRRS. UNIVERSITY OF EDINBURGH, ROSLIN INSTITUTE PHOTO


virus. With a series of pearls on a string, removing one pearl doesn’t destroy the rest of the pearls on the string, meaning that the remaining protein should still be able to perform its natural functions in the pig.” Tait-Burkard says that


protein CD163 works as an immediate immune response shield. It performs a number of functions involved in removing potentially harmful


substances from the blood, taking up bacteria to expose them to the immune system and organize and orchestrate the inflammation and immune response. The deletion of pearl number five was done using two genome editors. “We used two very specific


gene ‘scissors’ that cut the genome and removed the small piece of DNA in between them” she says. “The


genome editors are introduced as protein and RNA compounds that get degraded after a few hours in the cell so there is no trace of any other introduced substance in the pig.” The research team collaborated with Genus PLC, a leading global animal genetics company, to produce pigs with the specific


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