Pigs resistant to ASF and PRRS are on their way

The prospect of being able to raise pigs that have a high level of resistance to African swine fever (ASF) and/or PRRSv is getting closer, thanks to two separate programmes of research being carried out in Scotland and the US.

The ASF development is based at Roslin Institute, near, Edinburgh, while the PRRSv work is centred on the University of Missouri. In each case, current research is focused on the use of advanced genetic techniques to produce pigs that are potentially resilient to the diseases.

Starting with the ASF work at Roslin, the pigs involved there carry a version of a gene that’s usually found in warthogs and bush pigs, a step that the institute’s researchers believe may stop them from becoming ill from ASF. This is because while standard farmed pigs quickly become ill and die when infected by ASF, warthogs and bush pigs show no symptoms under the same exposure to infection.

Roslin’s research is focused on one of the pig genes associated with ASF infection, called RELA, that causes the immune system to overreact with devastating effects.

“Warthogs and bush pigs carry a different version of the RELA gene from that found in farmed pigs,” a Roslin spokesman said. “Scientists believe that this variant, which is known as an allele, may dampen the immune response and explain why they are more resilient to ASF.”

Researchers used a gene-editing technique to modify individual letters of the pigs’ genetic code, discovering that by changing just five letters in the RELA gene, they converted it to the allele that’s found in the warthog.

The work builds on previous research in which similar techniques were used to produce pigs with a single letter of their genetic code altered. This is the first time researchers have successfully swapped alleles in an animal’s genetic code using gene editing.

“Our goal is to improve the welfare of farmed pigs around the world, making them healthier and more productive for farmers,” the head of developmental biology at the institute, Professor Bruce Whitelaw, said.

The ASF work involves a collaboration between scientists at Roslin and Sangamo Biosciences, California, with funding from the Biotechnology and Biological Sciences Research Council and Genus plc.

Genus is also involved in the PRRSv development, having recently signed an exclusive global licensing agreement with the University of Missouri (MU) for intellectual property relating to PRRSv-resistant pigs.

This work also involves gene editing, allowing changes to be made in the genome of the animal without introducing genetic material from another organism.

“In the case of the PRRSv-resistant pigs, small changes were made to remove a single gene from the pigs that produces a protein, known as CD163,” Genus explained. “The CD163 protein is required by the PRRS virus for infection to occur.”

The company also stated that by using precise gene editing, MU has been able to breed pigs that don’t produce a specific protein necessary for the PRRS virus to spread.”

Of course, any public mention of such things as gene editing immediately raises questions about how this relates to genetic modification (GM), a point Genus also addressed.

“People using the term GM are often referring to transgenic genetic modification technologies in which the genetic material of the organism has been altered by the addition of genetic material from another species. These types of transgenic ‘genetically modified organisms’ would likely not exist if not for human intervention.

“However, the gene-editing technology used to create protection from PRRSv doesn’t involve transplanting genes from one species to another; rather it involves the simple inactivation of one of the pig’s gene products.”

Just about the only obvious downside from these two projects is that producers will need to be patient in waiting for the new high-resistance pigs to become available commercially. Genus has warned, in fact, that it’ll be at least five years until PRRSv-resistant pigs are available to pork producers.

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About The Author

Freelance journalist Colin Ley is Pig World's website news reporter