Leman: New nomenclature system for PRRS in US
System based on lineage and variant classification is designed to be more specific and reliable
14 April 2025
5 minute read
By: Dr. Paul Yeske, a veterinarian with Swine Vet Center based in Minnesota, USA, spoke to The Pig Site’s Sarah Mikesell at the 50th Leman Swine Conference in St. Paul, Minnesota, USA in mid-September 2024.
Paul, tell me about the change to the PRRS nomenclature system.
I'm speaking with Dr. Kim Vanderwall from the University of Minnesota, and we're talking about the new PRRS -2 nomenclature system. She's going to talk a little bit about what it is and how it was put together, and I'm going to talk about how we can use it in the field.
Why did the industry decide to make a change?
Traditionally, we had the Restriction Fragment Length Polymorphism (RFLP) system. It was developed early on in PRRS. As we started to understand PRRS, but the RFLP system wasn't necessarily designed to differentiate viruses, but it was a way that gave you a rough differentiation and probably didn't have the level of specificity that we need today.
The sequences always gave us the best answer and still do. When you compare two viruses, it is to compare the two sequences. What the RFLP system did was give people a name to call a virus. For instance, you might have heard of the 1-4-4 but there's multiple 1-4-4's. They're not all the same and so American Association of Swine Veterinarians (AASV) put together a working group and said we need to have a better classification system. One that is more repeatable and more dependable so that if I talk about a virus, you can understand exactly which virus I'm talking about.
The working group got together, and Kim led that working group from the technical side of going back and looked at a lot of sequence data from OR5 which we have a huge database of that information. She then considered a better way of doing it and produced the lineage and variant classification. It appears to be doing a very nice job of being able to identify viruses and they're repeatable and similar. It does a much better job of grouping them, allowing producers to give a name to the virus. For example, the L1C5 name means it's a line 1 variant C and 0.5 and so that's the classification of that particular strain, and it allows you to speak with someone else and say that's what I've got, and they probably will have similar experiences or at least similar comparison.
Paul, is this only for PRRS or will it be used for any other major viruses or diseases?
This is designed particularly for PRRS. It's not dissimilar to what they do with influenza, but influenza would probably be a little further down the road because there's been more work done with that with the human side, but this is designed specifically for PRRS.
Again, with the idea of having something that gets us into a system that is better and more reliable and that we can use to help answer those questions. For example, if I'm in a herd closure and I'm trying to eliminate the virus but I'm not testing negative when I'm supposed to, and those milestones aren't happening. Do I have a new virus or is this the original virus? It gives you a quicker method to determine if it’s the same virus or if it’s a different virus, so you will need to dig deeper to solve the problem. Or, if I'm in an area and looking at area epidemiology, it allows me to compare viruses within the area and say, that’s similar or no, it's not.
The other use that I can foresee for us is if we're using some of the killed vaccines and we're trying to use an off the shelf product, can we find something that matches closely, and we can use that to compare.
The other use will be, and hopefully we don't get to see that, is if we get a new emerging strain, hopefully that'll show up as a different lineage, and we'll be able to identify those new emerging strains maybe a little faster.
Will it look different to a producer or a veterinarian who's getting information back from a diagnostic lab?
They've started to report it on the nomenclature system particularly at the University of Minnesota. I think some of the labs are doing a combination where they do the RFLP and the lineage for a while as a transition until people switch over. There's still confusion even though you have both naming systems. There will be some transition here as we try and teach some of the old dogs like me new tricks.
What will this really mean for veterinarians and for producers?
Hopefully, it means better communication. We can speak more clearly about the viruses that we're dealing with so it should help with epidemiology. If you're in a herd closure and you're concerned you have a new virus, hopefully it helps make that a little easier and quicker. If we're looking for those new emerging strains, hopefully it will help us know that's coming. It's like everything with PRRS will probably evolve and likely will change over time but for now it appears that this system is working reliably and well. We'll just have to wait for that evolution to happen.
The nomenclature system is designed to be like a shorthand for the sequence and a more reliable shorthand than what we'd had with the RFLP system.
