March 9, 2021 – Dr. Kelly Diehl talks about salmonella in horses with Dr. Brandy Burgess, an associate professor at the Department of Population Health at the University of Georgia. The two discuss what we know about the bacterial disease, current management strategies and challenges it poses to veterinarians. Dr. Burgess also talks about her current Foundation-funded research, which is determining the duration of salmonella shedding among test-positive horses.
0:00:10.8 Dr. Kelly Diehl: Welcome to Fresh Scoop Episode 30, Salmonellosis in Horses. I'm your host, Dr. Kelly Diehl, Morris Animal Foundation Senior Director of Science and Communication. And today, we'll be talking with Dr. Brandy Burgess. Dr. Burgess is an Associate Professor in the Department of Population Health at the University of Georgia, and a Morris Animal Foundation funded researcher. Fresh Scoop is the monthly podcast of Morris Animal Foundation, one of the largest non-profit foundations in the world dedicated to funding studies to find solutions to serious health threats to animals. In each episode, we'll feature one of the researchers we fund or one of our staff members, discussing their work in advancing animal health. Whether you're a practicing veterinarian, technician or student, or just an animal-loving science geek, Fresh Scoop is the podcast for you. You can learn more about us at morrisanimalfoundation.org. Okay, so on to today's show.
0:01:08.5 DD: Today, we welcome Dr. Brandy Burgess. Dr. Burgess completed her DVM from Colorado State University, just up the road from us, followed by an MSc Internship and Residency in Large Animal Internal Medicine at the Western College of Veterinary Medicine, University of Saskatchewan, Canada. She then completed a PhD in Epidemiology and Residency in Infection Control and Biosecurity back at Colorado State University. She is a diplomate of the American College of Veterinary Internal Medicine, and of the American College of Veterinary Preventive Medicine, and has been faculty at the University of Georgia since 2017. Dr. Burgess' research interests focus on investigating the epidemiology of important potential pathogens in veterinary medicine and public health, including the exploration of risk factors and rapid methods for detection, as well as the development of evidence-based risk management strategies for the prevention and control of important contagious and zoonotic pathogens in veterinary medicine. So Brandy, welcome, and thanks for joining us today!
0:02:15.3 Dr. Brandy Burgess: Yeah, thank you very much.
0:02:17.8 DD: Before we get to your work, we always ask everyone to tell us a little bit about themselves and what led you to becoming a veterinarian.
0:02:25.2 DB: Yeah, yeah, the classic answer is I love animals. [chuckle] Yeah, so I grew up on a farm and really, I guess, did have a love of animals, and I liked science. And so I think veterinary medicine became sort of a natural fit for me, and I actually don't remember wanting to do anything other than that. And so that was sort of my path from the get-go.
0:02:45.8 DD: I think your pathway is probably similar to a lot of us. And to start, and can you tell us a little bit about salmonellosis in horses, things the people who are listening may not know, even if they're veterinarians or they've forgotten? A little bit like the scope of the disease, how it manifests, and the impact of the disease on horses and horse owners.
0:03:08.4 DB: Sure, yeah. So ironically, Salmonella in horses, we don't actually know that much about it and about the epidemiology. And so it's one of those diseases that can sort of sneak up on us. So horses can have clinical disease, so they can develop diarrhea, it's a GI disease, so they can develop diarrhea and get very sick and sometimes, even die from it. But a larger proportion of horses can actually just shed the bug asymptomatically, so they're not sick with it, but they seem to carry it, and so then they can shed it intermittently. And so therein lies sort of the challenge with this disease is, while we do recognize it as something that causes illness, it can also be subclinically shed and can pose a problem for other animals, so other horses on the farm, dogs and cats. And don't forget, it's a zoonotic agent, which means that they can be passed to people. And so that's why it becomes a real challenge when we think about managing this disease in our horses.
0:04:05.6 DD: I want to dive into your study, your Foundation-funded study now. And let's start by could you give everyone a high-level view, sort of, of the question you wanted to ask, and why?
0:04:21.7 DB: Sure, yeah, so this is something that really was in the works for a while. We tend to look for Salmonella in horses when they come into teaching hospitals or to veterinary hospitals, in general. It's a bug that can be a problem in that environment where we've got animals that potentially are compromised, and so they may be predisposed to infection. And so we tend to do a lot of surveillance sampling, so we look for that bug in horses. And when we do that, we tend to find it. However, we also then discharge those horses to go home because remember, a lot of them actually aren't sick with it. And so the question became, "Okay, if a horse is detected to be shedding Salmonella, how long do we expect them to do that? And what sort of an impact might that have on the home farm when we send them home?" So thinking about not only the people on the farm, but the horse's stablemates.
0:05:10.5 DB: So that's really where this came from. Our objective, really, is to determine the duration of shedding of Salmonella among previously positive horses. And the idea is then that we can give good or better guidance to veterinarians, to owners about how best to manage that animal when it goes home because it's not realistic for us to keep it in the hospital for multiple weeks when it's otherwise healthy. And so this study was designed to really answer that question so then, we could provide better guidance, and maybe not have to do so many fecal cultures on horses. So typically, we'll culture it out of the fecal samples, and that costs money. And so by estimating how long we think a horse might shed, we could sort of wait that timeframe, and then check and make sure they're done shedding, and then know how better to manage them.
0:05:54.8 DD: Yeah, you know what? I didn't think about it when I made that question, but it sounds a lot like what we deal with, with COVID and who's shedding, and how long, and stuff like that, so yeah.
0:06:05.8 DB: Yeah, yeah, one of the interesting things about the shedding with horses is that they can do it intermittently, and they could do it at low levels and so, it can be hard for us to find it. And so when we think about testing, one test usually isn't enough. We typically have to do more than one test before we feel confident that we've determined the horse's stopped shedding. And so that's the other challenge with this disease, is it's not just one sample and you're done; it's three to five samples. So if you start doing the math, that can be costly to the owner and be a challenge when it comes to managing this.
0:06:36.6 DD: Right. Can you talk a little bit about your study methodology? So you gave us all the background. What did you decide to do?
0:06:47.0 DB: Yeah, so this study really is a multi-center study. So while the, well myself, is at University of Georgia, and my co-PIs are around the US and other teaching hospitals and academic institutions. We have created a broad network of private practitioners that also participate in this study. And so what we're doing, really, is a longitudinal, cross-sectional study. So we're looking at a group of horses and we're going to follow them over time. And that's the key, is that we follow them over the time just over time to see when they stop shedding. And so once a horse is positive, they'll get enrolled in the study, and we'll collect a sample, basically, weekly from those horses. And so we send a sample kit out to owners. They collect the sample, ship it back to us. And then we culture it in the lab, and then report the information back to the owners and to the referring veterinarians. But the real neat part of this is that, really, it's a longitudinal study, so it allows us to get an idea of what that duration of shedding could really be. And it's not something we can do just by taking one sample. We really have to follow them over time.
0:07:53.8 DD: Which you just talked about this. Salmonella has a really wide distribution. There's no pockets of it. Is that correct?
0:08:05.5 DB: So Salmonella in horses, in the general horse population, if you, depending on the study you look at, a general sort of healthy horse population, it might only be about sort of 1% of the horses that are shedding. When we looked at horses that come into a hospital, we might be somewhere around 4% that are shedding. Now, that will vary geographically, so we do see some variation on the types of Salmonella that horses might carry, and we'll see some seasonality to it. So in the summer months, we typically see increased prevalence of Salmonella in horses. A lot of times, we think that's related to sort of stress, the heat stress and whatnot. And so we might see it in that sense. It is ubiquitous, though, we find it everywhere, but we will see sort of some waxing and waning of different strains of Salmonella in different areas at different times of the year.
0:08:57.0 DD: Okay, so that, yeah, I didn't, I guess I didn't think too much about that. And you're doing a different approach from other studies, but can you speak to some of the information that's already out there about what we know about Salmonella in horses?
0:09:12.2 DB: Yeah, so what we know about Salmonella in horses. [chuckle] As I mentioned, it's a bit limited at this point, and we're hoping to, of course, shed some more light on that. Really, it's just the basics that we've already touched. So horses can shed it intermittently, so that means that they might shed it on a Monday, but not shed it again until a Friday. They can shed it at low numbers. So if I only have one or two bugs in a fecal ball, I might not find it if I look for it. And so it can make it hard to find. And we know that a lot of horses will shed it asymptomatically or subclinically, so they're not actually sick. And so this can be a real challenge, not only for managing them at home, but then also think about mares and foals, where we have a mom that's a bit compromised because she's maybe filled out, and then we've got a baby that this is maybe the first time it's been into the environment and we don't want it to fall into a whole bunch of Salmonella . And so it becomes important when you think about managing different types of horses and the things that you might do to prevent transmission to something like a neonate.
0:10:12.4 DD: This is a little off the beaten track, but why do you think we know so little? This is not exactly a new disease, right? Even an old person like me who's a small animal vet, we learned about it in courses, obviously, in vet school, and we occasionally have to deal with it with the animals or small animals. Why do you think there's a gap in knowledge?
0:10:34.6 DB: Yeah, those of us that deal with horses and those of us that do infection control in teaching hospitals, this is a bug that can cause a lot of challenges for us. But I think part of it is it's not very sexy. It's not stem cells, it's not next-generation sequencing. And so sometimes, it can be harder to get funding for some of these basic clinical questions to understand what's going on with this bug. It's a critical piece of information, but oftentimes, it can be hard to find funding and support of that, which was what made this grant so good, is that we actually felt like we had a question that needed to be answered, a fundamental question that needed to be answered, and Morris was able to provide us funding to do that.
0:11:16.8 DB: The other thing, too, is the majority of horses shed this subclinically, they don't actually get sick. And so a few horses die, maybe it doesn't draw as much attention. If things are much more... If there's something fantastic happening, an outbreak of something at a boarding facility, that's a little bit more in the mainstream and in the news that draws a lot more attention. This can be pretty quiet. We'll see some outbreaks of Salmonella in breeding farms, but it doesn't get the media attention that something like equine herpes might get. And so I think that's the other thing that can make it so that these bugs, Salmonella or something else, might not... We just might not know as much about them because we just haven't put as much time and effort into learning about it.
0:11:58.9 DD: Yeah, I think people listening who aren't in the veterinary profession probably think of Salmonella as a food problem, right? And not...
0:12:07.9 DB: Yup, food safety, yup. [chuckle]
0:12:09.0 DD: Not really... And food safety. And just to give people an idea of the gyrations, if you have a positive horse come into a vet hospital, what you have to do to control…they're sick. They're not just coming in, and they're maybe asymptomatic. What does treatment involve? because it's a big deal.
0:12:33.6 DB: Yeah, so if a horse actually comes into a hospital and they have diarrhea, a lot of times, we'll actually manage them in a separate location. We'll put them in what we call isolation and trying to keep them separate from the other horses. But sometimes in private clinics, they could also be housed sort of in the main facility, they'll just be well removed from the other horses. And so what we'll do is we'll try to create some barriers so that we don't pass that along, so it's transmitted from the feces and fecal-oral, so he'll ingest it. And so then those horses can be quite sick if they've got diarrhea. And so we don't actually treat them for the Salmonella , per se; we're treating them for the side effects that result from the diarrhea. And so it's a lot of fluid therapy. We will typically use antimicrobials because we're treating them, we feel like they're... The lining of their GI tract might be compromised. And so some bugs that normally live in your GI tract might get across and into your bloodstream. And so we may treat them with antimicrobials for that purpose, non-steroidal anti-inflammatories, sort of the typical supportive care type stuff. But we don't treat them specifically for Salmonella , if that makes sense. So if a horse isn't sick with it, but just happens to be carrying it, we're not going to treat that horse with anything; we're just going to manage that horse differently.
0:13:51.7 DB: And we've actually done some work previous to this study where we actually followed up with horse owners on-farm to see what happened on-farm with stablemates, and whether or not they reported increased hospitalizations or diarrheal illness in horses. We did this in Kentucky and found that if people take some basic precautions, and try to create barriers, and not sort of go and clean that stall of a horse that maybe is shedding Salmonella and then going to a different horse stall, if we put some barriers in there to make that more difficult, we actually didn't see increased levels of disease in the stablemate. So we're not going to treat them for the Salmonella, but we'll manage them a bit differently. And we feel like in general, people can accomplish that at home, successfully.
0:14:36.4 DD: Which is great. And I think that speaks to, looping back around to your study, is when these guys get sick, they can get really sick. [chuckle] So if you're bringing a horse back to your... If you have more than one horse, it becomes an issue and certainly, I'll, just as a small animal person, we don't see Salmonella a ton, but I have seen a few cases, and it is bad when we see clinical cases. I've seen it in cats, rarely in dogs, but definitely in cats. And you're right, it can be a big cost for an owner, too, as well. So I wanted to ask you, and I know this is asking you to speculate a little bit, and sorry about that, but do you think some of your findings could have a broader application for other species affected by Salmonella?
0:15:30.4 DB: I don't know. I think the interesting thing with Salmonella is really sort of any animal can carry it. And certainly, I've done a little bit of work with Salmonella in reptiles, and that acts a little bit differently. But the things that are common themes is we do see intermittent shedding in any of the other animals that I've looked at. And there's plenty of reptiles, etcetera, that will be shedding it that aren't necessarily sick with it. So I think a lot of those themes are common. The thing that will be different is how long they shed it. And certainly, with Salmonella in horses right now, if we sort of look at our preliminary results, we're really getting out to sort of six to eight weeks that we might detect in in these horses. We'll see it longer in horses that were clinically sick with it, so had diarrhea versus horses that were subclinical or didn't have any symptoms. And we speculate, we don't...I haven't looked detailed into this data yet because we're just wrapping up the study now, but we speculate that that duration of shedding might be associated with the type of Salmonella that they're shedding, and we wonder whether or not it's associated with antimicrobial therapy. And so those two themes would theoretically hold for other species as well. And so that's something that we will be looking at in this data as well, to see what sort of an impact both antimicrobial therapy and the strain of Salmonella maybe had on duration of shedding.
0:16:55.3 DD: Right. And actually, you just brought up a really good point that may be worth talking about. I think if folks are listening and you hear the word bacteria, and then you go, "We don't give them antibacterials." Can you talk about some of the unique challenges that Salmonella poses as far as when we talk about antimicrobial therapy? And some of the shifts that have happened.
0:17:18.0 DB: Yeah, so Salmonella, when we look at the Salmonellas and we characterize them, so we'll look at the serogroups, so Salmonella has big groups called serogroups. And then within those groups, there's serotypes, which is a bit more of a refined classification. And so we'll look at those two things, as well as the antimicrobial susceptibility pattern for that isolate. It's interesting because depending on the region, sometimes, not only do the strains look different, but those sensitivity patterns will look different. A lot of the Salmonellas will be pansusceptible, so you could treat them with many different antimicrobials. But then we'll get some that arise that are multidrug-resistant, and those are the ones that are a bit more tricky. It doesn't make the bug more virulent or cause more severe disease, necessarily, but it will make it harder to treat. And don't forget, because this is a zoonotic agent, that if it's harder to treat in a horse, it will also be harder to treat in a person.
0:18:11.7 DB: And so that's the thing with the antimicrobial therapy. And part of, if a horse is just subclinically carrying it, I don't really, as a clinician, it's hard for me to justify treating that horse because there's not actually anything wrong with him. And treating with antimicrobials doesn't have...There are consequences to that. And so that's sort of the problems: We know they can carry it and theoretically, we believe that if we limit the amount of antimicrobials we use, we won't select for resistance. And so we'd prefer, if anybody gets infected, that they have a pansusceptible strain that's susceptible to basically, the majority of the antimicrobials we might choose. And so that's sort of the critical piece, is whether or not they're multidrug-resistant or not.
0:18:55.0 DD: Okay, so it sounds like with supportive care, there's no difference in mortality, that basically, we can survive an infection as long as we're supported, or...
0:19:05.9 DB: So generally, yes. The caveat to that would be that if an animal becomes back to remit because they have severe diarrhea and their gut is compromised, if that bug that crosses the barrier is a multidrug-resistant Salmonella , it'll make it harder for me to treat it. And that would be true no matter what the bug was.
0:19:26.0 DD: Okay, so sepsis might be a situation where you might have to administer antimicrobials, which just makes sense, right?
0:19:38.3 DB: Yes.
0:19:39.9 DD: But it sounds like for supportive, many individuals get better with supportive care. So I have a question for you that I don't know that you might know the answer to, but are there little typhoid Mary horses that have Salmonella? [chuckle] You said they intermittently shed, and that's a tough question to answer. Are they getting reinfected, or do they have it? And they just intermittently shed.
0:20:01.4 DB: Yeah.
0:20:03.1 DD: Do you know any more? What's sort of the current thinking about that?
0:20:06.9 DB: Yeah, so the current thinking is we speculate that there is likely a sub-population of horses that might be "typhoid Marys" that might carry it long-term and never actually clear it from their system. In practice, we don't actually know that, that that's true or not. Now, the interesting thing with the data that we've been collecting for this particular study is that we have all the isolates banked. We are characterizing all the isolates. And we have not only the isolates that we're following sort of these horses, and they get enrolled, we'll follow them for sort of six to eight weeks. Sometimes, when we get to the end of that timeframe, they're still shedding and so, we'll keep following them. We've also had a handful of horses that had stopped shedding, and then they had... The study's been going on for a couple years now, and so we'll have a horse that maybe was enrolled early on and then stopped shedding, and so had completed that portion of the study. But then maybe had a colic episode and started shedding Salmonella again, and so we re-enrolled them to follow them again. And so we'll have those isolates to look at, and we'll be able to make some comparisons around if that looks like the same strain that they had previously.
0:21:14.5 DB: Just subjectively, we've got a couple of horses that that looks like that might be the case, that they have the same strain that they had, originally. And if that's the case, then that would certainly suggest that they maybe have been chronically carrying it, or there could be an environmental reservoir somewhere on the farm or in the facility that they live that maybe is providing a source for the bug. And certainly, in veterinary teaching hospitals, you can look in the literature and see multiple outbreaks that could be linked to a reservoir of Salmonella in the hospital environment, so we know that that's a possibility. But certainly, we've got some, a few clues now that would suggest that there's potentially just a small sub-group of horses that this might be true in. We don't know why at this point, but it's something to certainly take a closer look at in the future.
0:22:03.2 DD: Right. Yeah, no, that sounds pretty interesting. And then it begs the question about whether, I think as we learn more about the gut microbiome.
0:22:12.1 DB: Yeah.
0:22:12.8 DD: I think we know that there are probably... We all probably have some bad bugs that are just kept in check, but... And I think you can speak to this better than I can. There are people really looking at the horse microbiome now, too. Humans, it's a big deal, but other species as well.
0:22:31.2 DB: Yup, yup, there's a lot of microbiome work. And so there have been some recent studies looking at the microbiome, both in the GI tracts, so the fecal microbiome, as well as the respiratory tract in horses to try to get an understanding of what's going on with those. And so yeah, as we start getting more of that data, we'll be able to understand a bit more about what's going on. And that's one of the ways that we could look to see if some horses are just harboring Salmonella as a "sort of normal inhabitant of its GI tract" that can become a problem if their normal flora sort of gets disrupted somehow, whether that's stress or antimicrobials, that then could cause disease or cause them to shed it. But that's one way that we can theoretically get an idea of how many horses maybe are carrying this, that there's...It takes a lot of samples before I can say for sure that your horse is no longer shedding. So there could be a reasonable number that we just don't even recognize it in.
0:23:27.7 DD: Right. And I know you have been doing culture on these guys. Are there... I'm assuming you can do some of the... When you look at the gut microbiome and you do PCR technology, is that becoming more normal for this disease?
0:23:47.0 DB: So as far as detection methods for Salmonella, culture is sort of something that's been around for decades, of course, and there's multiple different methods that you can use to culture Salmonella. And part of why I do culture, of course, is I want a live bug to then further characterize. And when I think about infection control, I'm concerned about bugs that can actually cause disease. So I typically focus more on the culture side of things. The other thing we're doing with the fecal samples from this study is we are banking some of the culture media to run PCR at a later date so that we can see if they were PCR-positive as well. And so PCR is just looking for the genetic material. And so it doesn't necessarily have to be a live bug. So some of these horses that are enrolled in this study were diagnosed by PCR, and some were diagnosed by culture. It really sort of depends on the lab that you use and the lab's protocol that they have in place.
0:24:43.8 DB: And then we haven't done any whole genome sequencing on any of the isolates, but that's something that we're interested in doing so that we can better understand how an isolate that we're getting from the same horse, over time, if it's the same isolate, or if it differs in somehow, a completely different isolate or if it's shifted, somehow, over time. And so that's something, because we have the isolates banked, we could look at in the future. But it's not... The whole genome sequencing for Salmonella is not something that's sort of in the mainstream for veterinary medicine, at least.
0:25:14.8 DD: Right, so well, thanks for reminding us about live bugs versus finding parts of bugs, which PCR often does. So as we wrap up, what do you think your take-home message, if you had to think about it for our listeners like veterinarians, owners, the folks, vet techs, when it comes to dealing with this disease, no matter where you're working or if you're an owner?
0:25:41.5 DB: Yeah, so I think part of our takeaway really is this idea that we know that they can intermittently shed. And right now, our estimates, based on the data from this study, are sitting in about sort of 42 days for a median duration of shedding. We don't expect that to change a ton, but it'll change a bit with the... When we look at the rest of the data. And so if you think about that, that means that you're going to ask an owner to sort of manage that horse differently for that long. And so I think it's an important discussion point with owners about the fact that they probably should be managing this horse differently to protect the other animals on the facility, as well as the humans there. But I also think that we already sort of looked at the impact a positive horse may have on a home farm, and we've done that with other collaborators, previously, but that's also another piece of this study, where we are following these horses forward in time with their owners to find out what happens on the farm.
0:26:39.0 DB: And we believe that we'll get the same answer, that if you take these sort of minimum precautions, creating some barriers, making sure you're using utensils on those horses and not the healthy horses to keep everything separate, that kind of thing, that we think you can manage this safely and effectively on a home farm. So it's not a reason to get rid of your horse; you just need to manage it appropriately. And so that's really the big thing that we want to get across because we don't want horses to be sold or anything when they don't really need to be. And so I think that's where we're going to go with this and hopefully, we'll have some media releases about it. We had a media release, I don't know, I want to say last year. There was an article about it that... And that's really where we want to go with this, is it's just you might have to wait six or eight weeks, but we think that you can manage that effectively and have a good result in the end.
0:27:31.3 DD: Oh, awesome! Well, Brandy, thanks so much for joining us today and telling us about this, I really appreciate it.
0:27:37.7 DB: Oh, you're very welcome. I appreciate Morris Animal Foundation support, of course. This was... The study was funded by a First Award, so it was my first big grant. So that made a big difference to me, certainly, in my professional career, and I've managed to train a few students off this grant as well. So it's made a bigger impact than we maybe sort of thought in the beginning, but it was certainly very much appreciated.
0:28:01.5 DD: Oh, great! And I'm going to be looking forward to reading more of your work on this. I think it's actually pretty fascinating, and like you said, a really important disease that just doesn't get a lot of press. [chuckle]
0:28:16.8 DB: Not unless you're contaminating lettuce, right? [chuckle]
0:28:19.0 DD: Right, right, exactly. So that does it for this episode of Fresh Scoop. And once again, thanks to Dr. Brandy Burgess for joining us. We'll be back with another episode next month that we hope you'll find just as informative. Let's face it, the science of animal health is ever-changing and veterinarians need cutting-edge research information to give their patients the best possible care, and that's why we're here. You can find us on iTunes, Spotify, Google Podcasts and Stitcher. And if you liked today's episode, we'd sure appreciate if you could take a moment to rate us, and that will... Because that will help others find our podcast. And to learn more about Morris Animal Foundation's work, again, go to morrisanimalfoundation.org. There, you'll see just how we bridge science and resources to advance the health of animals. You can also follow us on Facebook, Twitter, and Instagram. I'm Dr. Kelly Diehl and we'll talk soon.