Porcine reproductive and respiratory syndrome (PRRS), caused by Betaarterivirus suid 1, was first observed in the U.S. in 1987 and had spread to Europe by 1990.

Pigs that contract what was at first called “the mystery pig disease” are frequently left with an inability to conceive, see an increase in late term abortions, premature farrowing and stillborn piglets. Adult male pigs that contract PRRS will likely suffer from a low sperm count and an overall inability to father offspring.

In addition, piglets that are born alive to sows suffering from PRRS often die prior to weaning and/or show slow growth and development.

The virus is airborne and can be passed down from sow to pigs. It does not pose a threat to humans nor does it make eating pork a threat to human health. However, it has remained endemic, with 20% – 40% of U.S. breeding herds reporting an outbreak every year, according to the Morrison Swine Health Monitoring Project (PRRS Cumulative Incidence Beginning 1 July 2009).

While vaccination can control some of the clinical signs and reduce a certain degree of the viral shedding, and broad-spectrum antibiotics can help control secondary infections and symptoms, there is no cure. Unfortunately, this means that farmers who find the disease has infected their farrows often have to cull their entire herds to start again from scratch.

Dr. Randall Prather, Curator’s Distinguished Professor in the University of Missouri’s College of Agriculture, Food & Natural Resources, is working with that school’s animal science research center to save countless droves of pigs, the farmers who depend upon them and food security for all.

Prather believes that the answer is in gene editing – something he knows a great deal about. When a team of cardiac surgeons successfully transplanted a pig heart into a human patient in Maryland in January 2022, it was done using a gene edit developed by Prather.

The genetic fight against PRRS

Dr. Randall Prather

“We’ve been able to identify a protein called CD163 located on a gene in pigs with PRRS,” Prather explained. “For the PRRS virus to enter cells, it has to first locate this protein so it can have something to attach itself to.”

Using his lab’s gene editing technology, Prather and his team have been able to eliminate CD163 from the cellular surface, denying PRRS the foothold it needs to infect the pigs.

Prather has been breeding PRRS-resistant pigs and researching the effect of this genetic editing on them since 2015. He said that aside from the pigs’ new immunity to PRRS, they otherwise experienced normal lifecycles. “While it is a big change for the better, we are talking about changing a few letters in a genome of over three billion letters. The pigs were fine in all other respects,” he said.

Despite the good news for those raising pigs, Prather is frustrated by the actions of the FDA.

“The FDA wants to regulate this gene editing the way it regulates drugs,” he lamented. “DNA is not a drug.”

He pointed out that the FDA allows pigs that have been exposed to radiation to be sold for meat, and that mushrooms and soybeans have been edited in the same way without regulatory interference for years.

Prather wants to help as soon as possible. “They’ve estimated that PRRS costs North America pig farmers $600 million a year, and that estimate was made 10 years ago. And this isn’t just a money issue. It’s an animal welfare issue. It’s an issue for the producers and the psychological toll it takes on them.”

He described talking to small family farmers who have had to depopulate their herds and the stress that places on them, both financially and emotionally.

Prather fears that the FDA could delay the implementation of his work for a long time, comparing it to the process that AquaBounty Technologies had to undergo before its transgenic salmon won FDA approval. “That took 17 years… It might take an act of Congress to speed this up.”

“We’ve had success with aminopeptidase-N (pAPN) for gastroenteritis and anthrax toxin receptor 1 (ANTXR1) for the Seneca Valley virus. Likewise, with CD163 we can have an immediate impact on PRRS,” he said.

Prather makes his argument plain and simple, even if the science behind his research is anything but: “I just want to make it where pigs don’t get any viruses.”

For more information from the National Swine Resource and Research Center visit nsrrc.missouri.edu.

by Enrico Villamaino