Episode 38: PRRS farm surface contamination assessment through environmental sampling

In the podcast, Swine Extension Educator Sarah Schieck Boelke speaks with Ph.D. student Marcello Melini about his research on environmental sampling of farm surfaces to assess contamination of PRRS (Porcine Reproductive and Respiratory Syndrome) virus at various places both in and outside the barn. 

What is Minnesota's Swine & U?

University of Minnesota Extension Swine team gives research updates through podcasts.

Sarah Schieck Boelke: Hello, and welcome to Minnesota’s Swine and U podcast series, a University of Minnesota Extension Swine Program. Today's podcast is a research update on PRRS farm surface contamination assessment through environmental sampling. My name is Sarah Schieck Boelke, your host, and I'm a swine extension educator with the University of Minnesota. Joining me today is Marcello Melini, who is a second year PhD student in the department of veterinary population medicine.

Welcome back, Marcelo.

Marcello Melini: Thank you for having me for a second time on this podcast, and sharing some of our projects with you. I'm gonna tell you a little bit more about myself in the sense of, what I'm doing is I'm currently in my the end of my 2nd year as a PhD student. I'm focusing on PRRS related projects with doctor Cesar Corso as my adviser. And sometimes I'm also helping in the Morrison Swine Health Monitoring Project, also known as MSHMP, with some of their projects that are related with PED or PRRS or other type of diseases. And, from my, from me, I some information is that I was born and raised in Guatemala, where I got my degree in veterinary medicine and my master's degree as well.

And before I came to Minnesota, I worked for several years in different swine related companies and farms to improve the health status, management, and production of the pigs.

Sarah Schieck Boelke: Great. Thank you for, explaining your background to us again and also who you're working with. What topic will you be talking to us about today?

Marcello Melini: I'm going to share information about a project in which, PRRSt contamination in farm surfaces was assessed using environmental samples, and these were surfaces that were in some cases outside the barns, and in other cases, not directly inside the barns. They were not conducted in the rooms. They were conducted maybe in before coming into the the barn or just in the entry room or some corridors, but samples were not taken inside the rooms. So no close, direct contact with the pigs.

Sarah Schieck Boelke: Before we get too far here, are you able to share what was the funding source for this research project?

Marcello Melini: Well, this project was funded by the Swine Disease Eradication Center, the SDEC, and this, is has a name to discover and communicate information on swine disease transmission control and elimination.

Sarah Schieck Boelke: So let's get back to your research project here of the environmental sampling of PRRS. So can you give a brief introduction to this research study explaining why it was a valuable project to do?

Marcello Melini: As we know, the porcine reproductive and respiratory syndrome (PRRS), this virus can be transmitted by direct and indirect route. Pigs become infected through direct nose to nose contact or when they are exposed to PRRS positive saliva, urine, semen, nasal secretions, feces, and also mammary gland secretions. That's from the, again, the direct route. Now the indirect transmission refers to the exposure to contaminated fomites. Fomites are every contaminated object.

These are boots, coveralls, needles, vehicles, and also another indirect transmission is through aerosols. So as we remember, after this newly emerged variant of PRRSt virus classified as L1C 1-4-4 variant. More information was needed to help understand how we've got to be distributed so quickly throughout the Midwest. And one approach to gather information of PRRS virus was the contamination of surfaces on positive farms. And if this contamination could help the virus disseminate.

So we need to understand, if it can be carried from location to location from these contaminated sources, or if the personnel is playing an important role of moving PRRS from from farm to farm.

Sarah Schieck Boelke: Could you answer the question of how did you go about completing this study?

Marcello Melini: This study was conducted during the summer and fall of 2021 and the spring of 2022. And a convenient number of farmers were selected, and we included criteria that included, just well, either breeding or growing pig farms that represent the modern production practices in the United States, and they had to be located in the Midwest. They had to be confirmed to be housing L1C 1-4-4 variant pigs, positive through not only PCR, but also sequencing, that these farms had to be 4 to 5 weeks of postclinical outbreak. And we also set a maximum amount of samples that could be collected from each farm, also a minimum. So from this was from a group of practitioners who asked, okay, which area to think are most likely to be at risk of contamination of PRRS.

After these areas were defined, we began to use a protocol that is commonly used for influenza, in which we have sterile cloth with, putting a resealable bag with 20 milliliters of PVS solution. So we collect that one day before the sampling. We have all the bags ready, and then we go to a farm with the list of the locations, and we be begin to wipe depending on the surface. It could be 1 maybe 1 foot by 1 foot or area, or maybe 6 inches by 6 inches. It depends on the area or the whole area if it's a door handle.

So we wiped it with, using gloves. We wipe the area, put the gauze back into the bag, squeeze, pour the liquid onto sterile sterile, tubes, and then label these tubes. And between it's very important that in between samples, we have to clean our hands and also change gloves just to avoid cross contamination. And then transport all these, samples to the UMN VDL for PCR testing. So some of these areas where, for example, the mortality sled or the mortality carts, the entry room floor, either at the near end and at the entrance of the area or passing the bench if they had a bench. In some cases, some boots were also sample, door handles.

For the workers, some of the cars, the pedals, the steering wheel were also sampled. And, additionally, we try to do particle deposition sampling in which we put we place, aluminum foil in the 4 cardinal points of the farm around maybe 3 feet from each side of the of the barn. We placed this aluminum foil, waited for 1 hour, and then we collected the sample from the the surface of this aluminum foil to see if any, viral particles were being placed on top. And this was basically what was done for this study.

Sarah Schieck Boelke: So then were the samples or I should say the locations that you took the samples at, were those pretty standardized from site to site?

Marcello Melini: This was, they were standardized, but sometimes they were not always available. We tried to when we got to for the breeding farms, they were pretty standardized. Mhmm. For the nurseries and the grow to finish, some of them did have the anteroom with the bench. Some didn't have that.

They were just directly, so there's no division. So it's okay. We're gonna assume this is gonna going to be an entry room, and they'd all they didn't have a corridor for their mortality. They were using the same doors for taking out the dead. So it's, we try to standardize, but we have to accommodate the the number of samples according to the specific type of farm that we were visiting.

Sarah Schieck Boelke: I understand so you plan it to be standardized, but it was also going to depend on the farm and kind of how they had things laid out and everything at the farm.

Marcello Melini: Yes.

Sarah Schieck Boelke: Makes sense. So now that you shared with us, you know, kind of how you went about doing this project, what were the results?

Marcello Melini: So at the end, we had a total of 7 farms that were housing these L1C 1-4-4 variant, with positive pigs, and we also had 1 PRRS negative farm that we use as negative control. In total, we had 169 environmental samples. And just 6 of these 7 positive forms, we had at least one surface that was PCR positive. There was one positive farm but no samples had a positive result. And from these positive farms or these 6 positive farms, 19 out of 143 samples had positive results, for PCR with CT values between 25 to 37, so quite high.

So for us, it shows that there's presence of the RNA, but this might not be viable. We also did virus isolation in some of the samples, and there was no positive results. So from, 8 of the possible samples that originated from exhaust fan cones. I didn't mention this, but we also sample exhaust fan cones. So 8 of these samples were positive.

There were also positive main door, entry doorknobs, or doorknobs of the door leading to the mortality disposal corridor, and other positive surfaces were the entry room floors and the mortality carts and sleds, which these last ones make a little bit more sense because they have a lot of blood on them. So when because you'll find some PRRS because of the blood or that's what I'm assuming. And, again, 2 samples were tested for virus isolation. None could be grown. So we know that we can detect PRRS, but we don't really know if it's viable or not.

It could be, but the just the amount is just too low.

Sarah Schieck Boelke: So just so I understand, when you said that, for example, I think it was 19 out of the 143 samples that tested positive for PRRS, It was that you found the genetic material for PRRS there, but it wasn't necessarily infectious for PRRS. Is that correct?

Marcello Melini: Yeah. That's correct. Yeah. That's completely correct. It's there but If it has the capacity to be transmitted or infect pigs, we don't exactly know. But we know that it's been shared or been taken out of the of the room into surfaces that it shouldn't be there. Mhmm. I mean, just finding the, virus in doorknobs, that means, there is a chance of it being taken not only from the inside of the room, but to other farms as well.

Sarah Schieck Boelke: So what you're seeing is with this project, yeah, you kinda stopped at just finding the genetic material on those surfaces. It wasn't part of the project to see if that genetic material was viable. Is that correct?

Marcello Melini: We we tried. It was one of the well, on the purposes was also to try to determine if it was viable. But there's also another, I won't say problem, but there's something to take into account when sampling for in environmental samples is we're gonna have high CT values from the PCR. And these, results are not just what can be used exactly for virus isolation. For my understanding is for virus isolation, it is needed to have low CT values. Once we have above 25 or we even have some that are 25.4 or 25. Those were not being able to have some virus isolation. So it needs to be a higher concentration of, the virus in the surface. So, again, we know that there is enough to be detected, but not enough to assess in the state in which is, there.

Sarah Schieck Boelke: Okay. That makes sense. So you found genetic material, but it wasn't high enough concentration to see if it was viable.

Marcello Melini: Yes

Sarah Schieck Boelke: Okay, Thank you for that further explanation.

Based off of your results, what conclusions can be made from this study?

Marcello Melini: Well, again, as, that the detection of PRRS virus genetic material on surfaces, either on the outer or inner areas of a farm that house PRRS positive pigs. it can be possible using targeted surfaces for the sampling, and we can also have, conclude that this exploratory study provides evidence that bicontainment efforts to prevent the spread of PRRS virus, from infected farms needs to be reassessed. So, again, if, there are some surfaces that maybe I will not recommend to sample for environmental, and maybe the the type of material or the exposure to some elements just will degrade the virus. But there are some that have proven to us that are very reliable sources for sampling.

Sarah Schieck Boelke: So these results that you shared, why are they important takeaways?

Marcello Melini: Well, these results can help bring more understanding regarding some of the dynamics of this newly emerged, PRRS virus variant, the L1C 1-4-4, on the field level. This is more applicable and not in an, experimental sense, but directly on the field. And knowing it can be found on frequently touched surfaces tells us that biosecurity practices might need to be improved. Again, how often are we maybe washing our hands before leaving the the barns, or are we attending to our feet in the sense of the boots? If we found some positive samples from the entry room floor, that means even if it had a bench or it didn't have a bench, it's it can prove that it connects in the barn because some boots were able to put it there.

So, again, how are we taking care of biosecurity? Or or sometimes I imagine it's hard to be compliant of biosecurity. We have in the farm, we have a lot of activities. We have to not only check one farm, we have to check several farms in one day, and it has to be sometimes rushed. We have, to do, some emergency activities with the silos or the food distribution.

So we have to move quickly, and we just forget at some point biosecurity is in place. Or maybe no one's watching, so I can just this one time be quick and nobody would will notice. But, again, PRRS can be very opportunist. So it takes every help we can give it to exit a barn or infect a pig. PRRS we'll take it.

So are we helping the virus to exit the barns? That needs to be addressed.

Sarah Schieck Boelke: Right. Very good. I was gonna ask you about biosecurity because I believe you had said that of the farms that you tested, I think you said that one of them you didn't find positive samples. So I was gonna ask you, oh, does that mean that, you know, that farm was doing a really good job with their biosecurity and that's why you didn't find it on some of those surfaces?

Marcello Melini: Yes. I will say they might have better improvement of their biosecurity, but, it was in a breeding herd. So breeding herds, again, they are very, very strict in their biosecurity. In some cases, they ask for, or most of them in general ask for downtime, but breeding farms, they take it more seriously. The bench, the showers, everything's more to the point.

There's SOPs in place, that are being carried on by all the personnel. So to me, it wasn't that, surprising to see in a breeding herd. I didn't specify this, but it was a breeding herd. And I'm not saying nurseries or finishers don't take biosecurity seriously, but breeding herds, they just are on top of it. They have, like, these eagle eyes on the farm and just looking at everything, more closely.

Sarah Schieck Boelke: Yes. That makes that makes a lot of sense as to why that one was the farm that you maybe didn't find positive samples. Like you said, they tend to be a little bit more strict in their biosecurity so that they can keep high level of herd health.

So to wrap up our discussion here, are there any closing remarks that you would like to make?

Marcello Melini: So just remember that biosecurity has several components, such as biomanagement, bioexclusion, and bicontainment. In this project, we aim to better understand some aspects of the bicontainment regarding the PRRS 1-4-4 L1C variant. And the results from this study showed that this virus can be found on surfaces outside the farm or which come into frequent contact with farm personnel. And from this, we need to go back to the basics to have biosecurity protocols that are realistic and are easy to follow. In order to avoid, taking out microorganisms, not only birds, but others, from inside the farm to exterior areas and contaminating them. And in the sense that just putting the microorganisms out there. Right? If we can minimize this spread, we can help the reduction of the risk of PRRS dissemination.

Sarah Schieck Boelke: Very good. Those are good closing remarks. I like how you mentioned that, you know, we need to go back to the basics and review those biosecurity protocols because I think, like you mentioned earlier, you know, sometimes at farms, they get complacent, or maybe there's, you know, feed bridged up in a feed bin or something and you think, oh, I'll just run outside really quick to free up that feed so it runs through the feed line. It won't take me that long. I'm, you know, not gonna change boots. Just really quick do it. But unfortunately, some of those cases are opportunistic like you mentioned, and it doesn't take a lot of virus to have on the bottom of our shoes or on our hands or on our coveralls. And then we allow it to hitch a ride either outside of the facility or opening a doorknob. It's now on that doorknob or on the floor of the entryway, whatever the case might be. So that's a really good reminder for everyone to review those biosecurity protocols, make sure that they're realistic and easy for folks to follow so that they do follow them, no matter what they're doing in the barn.

Well, Marcelo, I wanna thank you once again for your willingness to record a podcast with me, and this time, sharing your research on PRRS Farm Service Contamination Assessment through environmental sampling. So thank you.

I want to thank all of those that are listening to the University of Minnesota Swine and U podcast. This has been Sarah Schieck Boelke, swine extension educator, along with Marcelo Melini, veterinary medicine graduate student.

To further connect with the University of Minnesota Swine Extension, please visit the swine specific web pages on University of Minnesota Extension's website at www.extension.umn.edu/ swine. And on those pages, you will find connections to our blog as well as our Facebook page.

To learn about research being done by our swine faculty in veterinary medicine, please visit their swine in Minnesota blog at www.umnswinenews.com.