Incurable virus doesn’t hurt new breed of pigs

"We were able to breed a litter of pigs that do not produce this protein, and as a result, the virus doesn't spread," says Randall Prather. "When we exposed the pigs to PRRS, they did not get sick and continued to gain weight normally." (Credit: U. Missouri)

A virus that makes it hard for pigs to reproduce and slows their growth costs farmers $660 million a year. So far, no vaccine has been effective. But now researchers have bred pigs that aren’t harmed by the disease.

Scientists have tried for years to determine how the porcine reproductive and respiratory syndrome (PRRS) virus infects pigs and how to stop it. Previously, researchers believed that the virus entered pigs by being inhaled into the lungs, where it attached to a protein known as sialoadhesin on the surface of white blood cells in the lungs.

However, two years ago researchers showed that elimination of sialoadhesin had no effect on susceptibility to PRRS. A second protein, called CD163, was thought to “uncoat” the virus and allow it to infect the pigs. In the new study, researchers worked to stop the pigs from producing CD163.

“Once inside the pigs, PRRS needs some help to spread; it gets that help from a protein called CD163,” says Randall Prather, professor of animal sciences at the University of Missouri. “We were able to breed a litter of pigs that do not produce this protein, and as a result, the virus doesn’t spread. When we exposed the pigs to PRRS, they did not get sick and continued to gain weight normally.”

“We edited the gene that makes the CD163 protein so the pigs could no longer produce it,” says Kristin Whitworth, a coauthor of the study in the journal Nature Biotechnology. “We then infected these pigs and control pigs; the pigs without CD163 never got sick. This discovery could have enormous implications for pig producers and the food industry throughout the world.”

While the pigs that didn’t produce CD163 didn’t get sick, scientists also observed no other changes in their development compared to pigs that produce the protein.

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“At the end of our study, we had been able to make pigs that are resistant to an incurable, untreatable disease,” says Kevin Wells, coauthor of the study and assistant professor of animal sciences.

“This discovery could save the swine industry hundreds of millions of dollars every year. It also could have an impact on how we address other substantial diseases in other species.”

The university has signed an exclusive global licensing deal for potential future commercialization of virus resistant pigs with Genus, plc. If the development stage is successful, the commercial partner will seek any necessary approvals and registration from governments before a wider market release.

Genus plc, the US Department of Agriculture, and the University of Missouri’s Food for the 21st Century Program funded the work.

Source: University of Missouri