Minnesota's Swine & U

Sarah Schieck Boelke:
Hello, and welcome to Minnesota Swine & U Podcast series, a University of Minnesota Extension Swine program.
Today's podcast is a research update on the length of time farms stay, naive of Porcine Reproductive and Respiratory Syndrome Virus also known as PRRS.
My name is Sarah Schieck Boelke, and I'm a Swine Extension Educator, with the University of Minnesota, and will be your host for this podcast.
Joining me today is Mariana Kikuti, who is a researcher in the Department of Veterinary Population Medicine.
To get us started today, Mariana, will you tell us a little bit about yourself, and also include who you worked with on this project?

Mariana Kikuti:
Yeah. So first of all, thank you so much for having me here, Sarah.
My name is Mariana. I just said, I have been a researcher here at the University of Minnesota since 2018, and I've been working mostly with epidemiology of swine diseases. And then in this project, in particular, this project was done with the MSHMP group, which is the Morrison Swine Health Monitoring Program, which is led by Dr. Cesar Corzo.

Sarah Schieck Boelke:
Thank you.
And so, I guess, I briefly shared kind of the title of the research that you'll be talking about today. But can you tell us a little bit more specifically about what research topic that you'll be talking about?

Mariana Kikuti:
Yeah. So this project is a very straightforward one. So PRRS has been, you know, endemic in the U.S. for a while, and one common hesitation that producers might have is:
Well, if I go negative for PRRS, how long does it take for me to get a new PRRS outbreak? So this presentation today is actually regarding how long, on average, swine breeding herds in the U.S. stay negative for PRRS.

Sarah Schieck Boelke:
And before we get too far here in our discussion I'd like to give recognition to who funded this research. So are you able to share how this research was funded?

Mariana Kikuti:
Yeah. So the MSHMP project, which was the main group vetting the research, is sponsored, or is funded by SHIC or the Swine Health and Information Center. So it's the main funding for this project.

Sarah Schieck Boelke:
Thank you. And we certainly appreciate those.
And in this case SHIC, who funded this project, because, as we know, but to help our listeners understand any research that we do at the University of Minnesota does take funds in order to do that. Whether it's the animals we use or the funding or other expenses that go along with doing that research. So we certainly appreciate our funding and sources for all in any
projects that we do.
So Next, can you give us a brief introduction to your research and explain why it was a valuable project to do?

Mariana Kikuti:
Yeah. So this research again was conducted by MSHMP. So the Morrison Swine Health Monitoring project actually monitors about 50% of the breeding currently in the U.S.
So we monitor several disease passes weekly for those herds and of course PPRS is one of them, right? So, again, PRRS has been around in the U.S. since 90s. We know through this project that about 20 to 40% of the breeding herds are positive to PRRS on any given day.
So it's a very impactful disease, right, in the U.S. swine herd.
And then several control methods are used, right? Such as you know you can try to do elimination. You can vaccinate. You can just keep re-exposing the sow to a wild type virus, perhaps to try to get them some immunity.
But basically for the sow, the herd that tries to eliminate PRRS from their herd,
what we did is, we were trying to look then at how long did they stay negative. Because we think, you know, that's valuable information for the producers to hopefully, you know, eliminate PRRS from their herd. So if I'm considering eliminating PRRS, I would like to know how
much time, on average, would I stay negative for PRRS.
So that's the whole idea.

Sarah Schieck Boelke:
Yeah, thank you for explaining that.
So next, can you share how you completed this study, and it might also be beneficial for you to also share what results came of the study as well.

Mariana Kikuti:
So again, we monitor PRRS in sows weekly for all of those herds that are enrolled in MSHMP.
And the way we monitor sows is through AASV PRRS classification, which basically goes from 1 to 4.
One meaning they have an ongoing PRRS outbreak and then four would be the herd that, you know, eliminated PRRS from their herd but also the animals that are in the farm that are 0, negative. So they are naive. So that's why we often describe this time in which the farm stays naive as well.
So what we wanted to do is of all the herds that they are monitoring, how frequently those farms went naive, and then how long did they stay in a naive class.
And then also, what was the first incidence, or the number of new outbreaks that occurred amongst only those ones that actually were able to eliminate PPRS in their herd. And then in terms of results, we actually found that about 1/6 of the PRRS that we monitor actually eliminated PRRS at some point since 2010, I think, to 2022, if I'm not mistaken was the period that we analyzed.
So about 70% of the herd were able to eliminate PRRS from their, you know, from their herd. And then of those, on average, they stay negative for about 2 years, however, some of them were negative for over 10 years.
So again it varies a lot, but the median or the average would be around 2 years. And then for the ones that, again went negative, stay negative for at least a few years. The PRRS incidence rate was about 23% meaning that for each 100 farms that we followed within a year, 23 of them would break with PRRS. And this is actually a very similar average to the national average of PRRS that we find, right? So this means actually, that number of new cases of PRRS is not necessarily higher in those sites that eliminate PRRS than in any other PRRS, in any other breeding herds, sorry.
So we found again that the PRRS incidence in this PRRS that went naive already are kind of similar to the national average.
So that's pretty much the summary of the results.

Sarah Schieck Boelke:
Thank you. So I think I understood what you said. So MSHMP has been collecting PRRS incidence from these farms for many, many years. Right?

Mariana Kikuti:
Yeah.

Sarah Schieck Boelke:
And then you in this project started looking at what these farms report as of 2010. Was that correct? And then looked at them to now?

Mariana Kikuti:
I think the years we were looking at, if I'm not mistaken, were 2010 to 2022.

Sarah Schieck Boelke:
Okay.

Mariana Kikuti:
About 10 years of data, a little bit more than 10 years of data.

Sarah Schieck Boelke:
I know you mentioned that there's a lot of different options that farms can do in order to, you know, eliminate PRRS from their herd. So did you take into account what some of those different methods were or was that not necessarily part of this project?

Mariana Kikuti:
Yeah. So we actually did look at, you know, if whatever you were using, or whatever their previous process was before eliminating for PRRS, if that would influence the amount of time you would stay negative. We didn’t find an association there, meaning that, you know, because of the AASV PRRS classification, you would actually go from 1 to 4, right? So basically the herd would be going from a positive class, meaning they have an ongoing PRRS outbreak and the animals are shedding viruses, to a 2 which is when they are starting to wean negative piglets but they still have some immunity there or exposure. And then to a 3, which would be the time in which they don't have a previous exposure anymore and they are not positive shedding anymore. So the majority of the sites that actually eliminated PRRS were actually coming from a class of 3 or a class within which they weren't shedding anymore. So we don't have a lot of variation in that sense.
That's why perhaps we didn't see a lot of anything this time that they stay negative.
Yeah, but that's just mostly, you know, the standard way to classify PRRS processes in the breeding barn. So yeah, most of them are going to follow that pattern.

Sarah Schieck Boelke:
Yeah, thank you for clarifying that.
So based off of the results that you found with looking at the MSHMP data, what conclusions can be made?

Mariana Kikuti:
I think one conclusion is that we do have a significant amount of sites that actually are able to eliminate PRRS, right? Because that's something that’s very hard to do, in a sense, because we just have in some situations a lot of disease pressure.
But we do find that quite a few sites are able to eliminate PRRS and then for the ones that do, they can expect to remain negative for about maybe 1 to 3 years. But then again, some say for much longer. So it is kind of like, you know, how long would you expect to be able to maintain a negative class for PRRS?
But then also again, as I mentioned, for the sites that do eliminate, the PRRS incidence is not different than the national average.
So eliminating PRRS doesn't necessarily put you at risk of having more PRRS outbreaks, right? So that’s another important takeaway of this study.

Sarah Schieck Boelke:
So based off of the conclusions that you made from the results. What are some important takeaways from this research project?

Mariana Kikuti:
I think the important takeaway here would be that, you know, for sites that are trying to eliminate PRRS can have some perspective of how much time you're gonna be able to stay negative on average, which I think is really important if we're trying to make the decision on, is it worth it to pursue elimination or is it worse for me to try to maintain a continuous exposure to a virus, whether it is through vaccination or through live inoculation to try to keep PRRS out of the herd, right? So I think it gives us an important insight of how long would you expect to stay negative, which is the time to eliminate PRRS from the herd.

Sarah Schieck Boelke:
So that makes sense. So what you're saying is, yeah, based off of the results that can help the farms determine, maybe, what elimination or treatment methods that they're going to use. Is that right? Whether they just want to kind of keep, I shouldn't say keep PRRS, but whether if they want to completely eliminate it or know that they kind of have an underlying presence of it. Would that be a good way of thinking about it?

Mariana Kikuti:
Yeah, it is very common, particularly in very high dense regions, that some production systems might opt to maintain some level of herd immunity of PRRS. And then to do that, they would either vaccinate or do a live virus inoculation. So that way you're kind of reintroducing a PRRS virus every now and then in your population. So the animals are completely naive and the elimination process goes further than that. Right? So you're trying to eliminate everything. The animals are going to be completely naive. They’re not going to have any previous exposure to PRRS. So it is an important management decision that people have to do.
So I think understanding, you know, how the elimination plays off, I think it's important to help make those decisions.

Sarah Schieck Boelke:
Thank you for further explaining that.
So before we wrap up our podcast here. Is there anything else that you would like to say? Maybe there's a question that you wished I would have asked, and I didn’t, or maybe there's some more information that you would like to share that you haven't had a chance to do that yet.

Mariana Kikuti:
Yeah, I think I would like to share mostly the limitations of this study. Right? Limitations of studies are always a very important thing to discuss.
For this study in particular, we weren't able to assess other factors that affect the decision to pursue elimination. We just looked at the ones that eliminated from their herd.
So, for example, if they are in an high density area or not potentially inside their decision to try to pursue elimination. So all of those other factors that could potentially affect if and how long they are negative, for we didn't necessarily look at those. And then the other thing is, also we mentioned that the PRRS incidence rate is kind of similar for the ones that eliminate to the overall national average. But we also didn't look at factors that could potentially be important if you eliminate, which is, for example, increasing the overall health of the herd could potentially improve performance, right? So we also didn't look at that aspect of eliminating PRRS from the herd.
We mainly looked at time that they stay negative. But again, if you eliminate an infection of PRRS, you can potentially increase the performance of the herd, just because you know, you improve their health overall.
So we also didn't look at those things, but those are also important discussions to have.

Sarah Schieck Boelke:
Those are really good points that you mentioned. And I want to thank you, Mariana, for sharing your research on the length of time farms stay naive of Porcine Reproductive and Respiratory Syndrome Virus also referred to as PRRS commonly in the industry.

Mariana Kikuti:
Yeah, thank you very much, Sarah.

Sarah Schieck Boelke:
And I want to thank all of those listening to the University of Minnesota Swine & U Podcast. This has been Sarah Schieck Boelke, Swine extension educator, along with Mariana Kikuti, a researcher in the Department of Veterinary Population Medicine. To further connect with the University of Minnesota Swine Extension, please visit the swine-specific web pages on the University of Minnesota Extension’s website at www.extension.umn.edu/swine. On those pages you'll find connections to our blog as well as our Facebook page to further connect on research being done by our swine faculty in veterinary medicine, please visit their Swine in Minnesota Blog at www.umnswinenews.com.