August 17, 2020 – Dr. Kelly Diehl talks with Dr. Anna Jolles, an Associate Professor in Epidemiology at Oregon State University. They discuss tuberculosis in African buffalo and Dr. Jolles’ Foundation-funded work to understand how disease interventions for TB can affect population health in the long run.
00:09 Dr. Kelly Diehl: Welcome to Fresh Scoop, Episode 23, "Tuberculosis, Parasites, Wildlife and the Costs of Infection". I'm your host, Dr. Kelly Diehl, Morris Animal Foundation Senior Director of Science and Communication. And today we'll talk to Dr. Anna Jolles, a Morris Animal Foundation-funded researcher and epidemiologist. Dr. Jolles is a professor in the Carlson College of Veterinary Medicine and the Department of Integrative Biology at Oregon State University.
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 either 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, on to today's show. Today, we welcome Dr. Anna Jolles. Dr. Jolles completed her PhD in Ecology and Evolutionary Biology at Princeton University, and she received her bachelor's degree in Zoology from Oxford University.
01:27 DD: Dr. Jolles did a postdoc at the University of Groningen, I hope I said that right, in the Netherlands. And since 2008, she's been at Oregon State University, as we previously mentioned, with a split appointment in the College of Veterinary Medicine where she teaches epidemiology and in the Department of Integrated Biology where she teaches disease ecology. Dr. Jolles' research interests include understanding how environmental variation, animal factors such as behaviour, physiology and genetics, and the multitude of infectious organisms that wild animals are exposed to influence the health of wildlife populations. In practice, this involves using a blend of field observations to discover natural patterns and controlled experiments to identify mechanisms, as well as mathematical theory to generalize these findings. We apply these approaches to a variety of wild mammalian species and a broad range of pathogens and parasites, and that dovetails with many of the grants that Dr. Jolles has received from Morris Animal Foundation. So, these include African Buffalo, which have been her flagship study species, but also African lions and most recently, desert bighorn sheep here in the United States. So Anna, thanks so much for joining us.
02:48 Dr. Anna Jolles: Thanks for having me, Kelly.
02:50 DD: Before we get into your work, we just discussed all of your very impressive credentials, but can you tell us a little bit about yourself and your background?
03:00 DJ: Okay. Well, I grew up in Europe, partly in Britain and partly in Germany. My parents are split that way, a German and a Brit. And I also spent a lot of time already as a girl in South Africa because my dad moved there when I was 15 years old, and so I'd go and spend summers there with him, which was really my introduction to wildlife. South Africa has amazing wildlife. I started studying in Germany and actually started with physics, which was really interesting. But I soon found out it wasn't very relatable and it was important to me to contribute something that actually mattered to a lot of people, and so I switched to biology and went off to Britain to Oxford University. I came to the States for graduate school. Principally, well, partly out of curiosity because new places, new people are always really interesting to me, but also graduate school is structured differently here and you have a lot more freedom to pick your own research directions already as a student than you would in Europe. And so, that attracted me to coming over here. And really then, everything followed from there with finding different projects and mentors and collaborators, and then eventually a husband and a family. And so here I am on the West Coast now for a bunch of years already, still studying wildlife diseases.
04:29 DD: So what drew you especially to epidemiology? And can you explain... A lot of folks listening probably understand something about epidemiology because I think with the COVID pandemic we're learning more about it, but can you explain a little bit about what an epidemiologist does and what drew you to that discipline?
04:48 DJ: Right. Yeah, you're very, very correct that people have had this crash course in epidemiology recently. And my course this spring for the vet students, veterinary epidemiology, I felt like I didn't really need to teach them that much at this point because they've heard it all in the news all the time. But basically epidemiology is population health. Rather than focusing on the individual animal and its symptoms and treatments for individual cures or disease prevention, epidemiology is about understanding what a disease is going do to a population, how it spreads in a population, how that might be stopped or reduced. And so for me, well, I was lucky to have really a lot of choice in what I wanted to work on, and I think that's a huge privilege. And I was unsure initially when I started grad school which direction I wanted to go in. I was sort of motivated by two things, one is just curiosity-driven. There's so much that's interesting in biology, and it's just basically understanding how the natural world works. But the other motivation, of course, is trying to contribute something positive to saving what's left of that natural world.
06:06 DJ: And so in my first year as a graduate student, I managed to get myself set up with a small project that took me around a bunch of different parks and natural areas in South Africa, and it was just a short project and designed as such. It was to do with a rhino horn and identifying where it came from, sort of help with stopping smuggling. So I was looking around for rhino poop and plants that rhinos eat, and it was just a summer number one project, but what it did for me was it allowed me to talk to a lot of wildlife veterinarians, other wildlife researchers, and wildlife managers across a lot of different parks and focused on different animal species in different habitats about what they felt were the challenges ahead and where more research would be needed. And so one topic that came up again and again was wildlife disease and that there are just a lot of really large gaps both in how these diseases work in wildlife populations, but then also in trying to understand what their impacts would be for wildlife conservation. And so that is what I ended up focusing on.
07:19 DJ: Now, the curiosity driven part of that is that epidemiology and disease ecology really combine a lot of pieces of biology, so it's impossible to get bored because everything matters. Animal behavior matters because diseases spread through contact. Animal genetics matters because there's giant amounts of variation and susceptibility to different diseases. Community ecology matters because actually there's loads of parasites and pathogens out there, and they all interact in their effects on the host. And so really physiology, immunology, you can pick all kinds of directions in biology and they're all important in understanding the spread of diseases in natural populations. And so I thought that that was just absolutely fascinating and would allow me the leeway as my career went on to move between these different directions and areas and really get a broad view of what was happening in these populations.
08:18 DD: I know that we discussed... You've had a real wide range of interests and one disease that I think a lot of people don't realize affects wildlife is tuberculosis, and you've done a lot of research on that. And can you tell us as a group the tuberculosis in animals, and the scope in wildlife, and why it's an important problem for wildlife?
08:49 DJ: Yeah, TB is a really well-known human disease. And in people, of course, it's caused by an organism, a bacterium called Mycobacterium tuberculosis, and it causes really chronic disease. In some people it stays totally asymptomatic, whereas in others, it can cause progressive lung disease, respiratory disease, and also wasting disease, where badly affected people will lose a lot of weight and just become weaker. And so in wildlife TB is caused by, typically, a close relative of M. tuberculosis called Mycobacterium bovis. So they really are genetically very similar, but M. bovis is more transmissible in animals than is M. tuberculosis. So human TB can spillover into animals and it does happen in zoo situations typically, but mostly in natural populations, TB in animals is caused by M. bovis. And so M. bovis is an interesting organism, it has a really broad host range.
09:51 DJ: So it can infect pretty much any mammal species, but the outcome for the animals is variable by species. For example, a zebra can acquire M. bovis infection but it doesn't seem to do very much to the zebra, they are very tolerant of it. And at the opposite extreme there you have predator species such as lions that do really very poorly with M. bovis infections, so they show a similar disease to what you might expect in a person. It's also lung disease, it's also wasting, although in lions additionally, you have scratching and biting transmission, and so you get more lesions associated with that, skin lesions and such. But they waste way quickly and it's quite lethal in lions. Now buffalo, my study species, are somewhere in between there. Buffalo can carry TB for years, but it does reduce their survival, even though they don't waste away as quickly as a lion might.
10:50 DJ: And so the reason that's important in wildlife is really in a couple of different ways. One is the direct effects on the health of the animal that has the TB, which like I said, can be very variable and just depends. So the main concern with Buffalo TB from a conservation point of view has often been actually the health of lions, because they are their main predator and populations in restricted reserves are quite small, and so you can't really afford to have another big mortality factor on these small populations of predators. But then there's indirect concerns as well. Populations of large mammals that are increasingly stuck in quite small reserves often need to be managed genetically, where animals get moved around between reserves to keep the genetic health of the population going despite these tiny isolated populations. And so, certainly in southern Africa, that has been part of managing a lot of large mammals, is to supplement populations by quite carefully kept records of who gets moved where to maintain genetic diversity.
11:58 DJ: And so TB throws a wrench in that. Because once you have TB in the system, then of course you can't move those animals because you might get another park infected. So that really complicates metapopulation management of wildlife. And then the other part of that, too, is that once you have TB in a system, your conflicts between conservation interests and the agricultural landscape around that are really magnified because TB can then spill back from the wildlife into livestock potentially. And so that really sharpens that conflict a lot, which is again something that conservation cannot afford.
12:36 DD: You talked about the African Buffalo as one of your key species for studying this, and I want to turn to some of your foundation-funded research. And just so the audience knows, Anna's done a lot in all the species she just talked about, including African lions, but we'll focus on the buffalo. And can you talk a little bit about the studies focused on these guys and a little bit about your research questions?
13:07 DJ: Yeah. There was a Morris Animal Foundation grant that a student of mine, a grant student of mine, Hannah Tavalire, and I managed to get, which supported some really interesting work on tuberculosis in African Buffalo. So we were interested really at the end of the day in understanding how disease interventions for TB are going to affect population health in the long run. And so what happens in wildlife populations where managers decide that they do want to limit the spread of tuberculosis is that typically they will test animals and then remove the infected animals and release the uninfected back into the population to reduce the spread, maybe prevent spill over to livestock or to predators, and just generally keep this in check. But there might be interesting and important side effects there because in this case then, the management is exerting a stronger, selective pressure on that wild population than the disease itself because just a positive test will lead to the removal of that animal, which may very well have survived for a long time still without the management and, of course, may have spread the disease too but also would have contributed still to reproduction in that population.
14:25 DJ: And so the genetic consequences of removing animals for disease control are not something that's usually considered because it's very much more long-term than the immediate, "Oh, we need to stop this disease," that's in the forefront of the drivers behind these programs and which are valid. And so we set out to do some foundational research to try and understand better what would happen to population genetics and genetic health when lots of animals are removed for a particular infectious disease. In this case TB, but it could be any other infectious disease you try to control. And so our research questions were that first we wanted to characterize the phenotypic variation in responses of buffalo to TB, so from being killed by it quite quickly to surviving for many years. All these outcomes exist in buffalo. And then also to see what the heritability of this variation is. And then second, if it was heritable, then we wanted to look for genes that would drive those phenotypic variation, these different disease outcomes in the animals. And then ultimately to assess, "Well, when we select out infected and early infected animals, what will that do to that genetic diversity that we're looking at?"
15:46 DJ: And so, in our case, we were lucky enough to be able to piggyback onto a big study that had been going on for a few years where we were tracking wild buffalo, 200 of them, and measuring their TB status every six months. So that would give us the opportunity to then look at variation in TB response, and then the Morris Animal Foundation funding allowed us to do the genetic work on those buffalo that we had been tracking.
16:19 DD: And what did you find and did anything surprise you when you looked at this population?
16:27 DJ: We found a ton of phenotypic variation. We found lots of variation in how quickly animals get infected. The population that we were studying in the southern Kruger National Park in South Africa had quite high prevalence of TB and so animals would, in those herds, all be exposed sooner or later, and actually sooner than later because the prevalence was so high. Buffalo are very social. But some of them managed to hold out without becoming infected well into their adulthood, whereas others got infected before they were two years old. So there's lots of variations there. Also, lots of variation once they were infected, how long they survived with that infection. Many of them survived past the four-year span of our study, whereas others succumbed in the first drop year that was included in that study. We also found that co-infections with other pathogens and parasites might make a really big difference to those disease outcomes for TB infected animals. So specifically gastrointestinal worm infection makes a big difference. If the animals didn't have worms, they survived much better with TB. So there's some unexpected sorts of correlations between very different pathogens and parasites here.
17:47 DJ: When we look for genes for resistance, well first off, it was kind of surprising that we were able to find some, to be honest, because this was not a huge study, we don't have thousands of subjects like they do in human studies. We had a couple hundred buffalo for which we had TB data. And then when you narrow that down to those that actually did get TB or didn't get TB versus having indeterminate outcomes, then that number gets smaller. But we did find two genetic loci that had effects on when an animal acquired TB, we assume that they're all exposed, they're all in the same herds. And so is that we called animals resistant if they managed to hold off infection for longer and not resistant if they acquired infection quite early when they were two to three years old or less. So we found two genetic loci that modified that likelihood of becoming infected per year in combination by up to ninefold. So those are huge effects. That's why we're able to find them with our relatively small number of buffalo. So that was surprising that these would be such strong genetic effects and they were not genes that had been described or the analogous had been described in other species before.
19:03 DJ: We also found that there was a lot of variation in tolerance, so how the animals did with TB, and their sample size was too small to really get to the genes because that's then the subset of animals that got TB and for whom we know outcomes. So there's more work to be done with that puzzle. Yeah, so I would say the main surprises were how strong the signal was for variation in resistance and that the other genes that were not the same as in other species.
19:32 DD: And... We've chatted before about this, because I think one of the things that really intrigued me was your discussion of, "Oh, the costs of fighting infection," and this is I think really, really interesting, which is, can you talk about when your body attempts to eliminate TB, it's not always a great outcome when you try to do that. So can you explain that? because it's really fascinating.
20:11 DJ: Right. Yeah so the underlying idea here is that really nothing's for free, right? So you can have this variation among animals and who is more resistant and who's less resistant to acquiring TB or who does better when they get TB than some of the others that lose condition more quickly. And so then one would wonder perhaps why the selection by infectious agents hasn't just led to all animals being the more resistant type, or all animals being the more tolerant type. Why don't they all do better with disease when that is biologically possible, and so that's where that idea of trade-offs comes in, but there's always a cost to the animal fighting disease a little bit better than its conspecifics. And so what we found when we looked at our more resistant animals, so they managed to hold off TB for longer than some other buffalo, but once they got TB, because there was really high disease prevalence in that population. It's not total resistance, it's just more resistant. So if those animals did get TB, then they actually did really poorly. They lost condition faster than the non-resistant animals that had acquired TB earlier.
21:27 DJ: And they had a higher mortality rate as well than the genetically less resistant animals. So there's a really interesting balance there, right? Where TB resistance might be positive and might be selected for perhaps in populations where there is some TB, but it's not really rampant because then those animals have a good chance of reproducing during a relatively long life span before they acquire TB if they do at all. And so then that genotype would increase in the population. But if you have a population where TB is really very common, then even that extra protection that these more resistant animals have, isn't actually going to prevent them from getting TB, they're going to get it anyway. And if they get it early enough because it is so very common in the population, then it might actually be a negative because their lifespan with TB is much reduced compared to the animals with the less resistant genotype. And so it's these balances, depending on the circumstances, right? How common TB is and probably also depending on how well-fed those animals are, that keep diversity in that gene pool.
22:41 DD: Okay, yeah, it's a pretty interesting, your finding. Because if we think purely from a natural selection standpoint, right? It doesn't make sense that these guys wouldn't have been eliminated a long time ago. But I thought it was really helpful observation to maybe put an explanation about why this hasn't been eliminated from wildlife because of this trade-off sort of that they have. So just thinking about your findings then, and maybe this is unfair, but to extrapolate a little bit, how do you think this might help, circling back to your original concept, which is we've got to manage these herds sometimes, we've got to manage animals, and Morris has several grants that deal with moving, what are the costs of moving animals around, right? Everything from how do you safely transport them to the idea that we could be introducing disease. And so how do you think your findings might help people when they conceptualize how to manage these, as you pointed out, very small groups sometimes?
23:56 DJ: Right. So again, I think that arises directly out of that discussion of tradeoffs, right? Because when we take out animals from a population based on a positive test for a disease, such as TB, then we're not distinguishing whether we're taking out the more resistant animals, but they were unlucky and got disease anyway. Or the less resistant and we will unbalance, probably be taking out more of the less resistant genotype because they get the disease earlier. So you're more likely to find them being TB positive, you're also more likely to find them because they survive better with TB. Whereas the resistant ones would have perhaps died before you tested them. And so that management action will have a sort of directional selective effect on that population selecting for a particular disease resistance or non-resistance genotype. And so we're narrowing with this management, potentially the portfolio of possible responses that the population has to this disease, but then also to other diseases. Because it's not unlikely that some of the responses that are helpful for TB are also helpful for some other pathogens and some that are unhelpful for TB, may have interesting and important effects for other pathogens.
25:23 DJ: And so I think the lesson there in terms of management is that there's often a balance in trying to help with immediate effects of a disease and limit its spread, limit mortality from that disease versus also bearing in mind, the long-term health of that population and that we really typically don't know enough about what genes we need to be preserving and so on should perhaps have a conservative approach there where if we don't know how it works, then we would rather preserve a lot of genetic diversity than take that risk of narrowing the gene pool down a whole lot.
26:04 DD: Right. And I'm going to ask you to stretch again, do you think your research has anything to teach us about human TB, which I think... For us living in the United States, for people in Europe, it seems like this really vague disease that happened, consumption, and we have all these romantic operas and novels about it, but it's a huge issue in most of the world, right? It's still a big cause of mortality in people, in lots of countries, and we do not a great job, it's a weird disease and we still are fighting it. So what do you think your findings might speak to the variety of responses as you alluded to earlier in human TB?
26:57 DJ: Right, yeah. So, one wouldn't want to over-stretch that too far, but then on the other hand, much of what we do in terms of human infectious disease research is done in mice, and they're not really more similar to a person than a buffalo is, so maybe it's fine to study buffalo. So you're right, TB is a really weird disease because in people too, the outcomes are so variable, it's kind of similar to what we see in animals and M. bovis are actually a reasonable model system for human TB and that the course of the disease and the pathological symptoms that go along with it over time, are much more similar than in most models. So in that sense, having a study system in a buffalo or even a domestic bovine can be used for that, they're of course harder to study because their lives are long and they're big and all those logistic issues.
27:58 DJ: So, as far as our particular findings, probably the most relevant to people was actually to do with a co-infection result that was related to this Morris-funded study, because some of those genes that we discovered here, a subsequent work has shown that they actually mediate that interaction between gastrointestinal worms and TB potentially. And so, that piece really showed that co-infection by worms makes TB much worse and that's a well-known finding in people also, but what was new here was that when we treated animals for worms, it didn't actually prevent them from acquiring TB. And so, that was a discouraging result as far as using antihelmintics in human populations and hoping that it would control TB, but it might very well, make the effects of TB much less scary for people, and so that was the upside of that piece.
29:07 DJ: As far as the genes that we found specifically in the buffalo, I wouldn't expect them to be analogous in people, but I think the takeaway there probably is that this is a pretty complex host-pathogen interaction, and there's much that we don't know yet even about the mechanisms that occur and they're not necessarily discoverable in lab animals, in its entirety. So I guess the takeaway is a guard against hubris, about what we do understand and what we can understand from using a very reductionist approach where we control all the factors of an animal's life and we control the specific strain of infection that we give it and we control whether it's got other pathogens, because what we're seeing here is that outcomes vary a lot according to the animal circumstances and according to the variable genetics that you have in a natural population, which would also be the case in people. And so, some of the puzzles in human TB, the variable outcomes and also the variable vaccine responses, TB vaccine seems to work in some populations quite well and really not at all in others, that the environmental variation that those populations are exposed to, and their genetic variation might contribute to why we see these different outcomes of vaccinations and different potential for a disease control using that.
30:39 DD: Thanks. It's a pretty unusual... It's an interesting disease. What's next for you do you think? Like where do you want to go next with your research on that?
30:50 DJ: Well, so there are some loose ends to tie up with this buffalo TB story and we're working on those. Some of them relating to what the evolutionary trajectory will be or might be for these wildlife populations, given the trade-offs that we found. And there's actually a follow-up study that we hope to do if we're ever able to do field work again, [chuckle] that would help with those... Understanding those evolutionary relationships, my newest project that is just starting up, and so that is the near future for me is a study in desert bighorn sheep, where we're taking this idea of how do diseases spread and what does the context in terms of co-infections due to that spread, we're taking that to the metapopulation level, so bighorn sheep are a great study system to address that sort of thing, because they are naturally in fragmented populations, so they like to live on mountain tops, separated by a low-dry desert that they don't like to cross very much, but do occasionally. And so, diseases tend to circulate within each somewhat isolated population, but sometimes they can then make the leap to the neighboring populations, and so there, we'll be looking again, a trade-offs between isolation, protecting populations because diseases more rarely get there, versus isolation, putting populations at risk because they...
32:31 DJ: The most isolated populations also have the lowest genetic diversity. And so that's really the crux for that disease management questions, right? What should I emphasize trying to stop the disease or trying to allow the population to remain genetically resistant to a broad variety of diseases. And so, we're trying to get to that question empirically in this, there's a bighorn system where pneumonia is the main sort of very acute disease threat, but of course, like any wildlife species, they get infected by a lot of things, and so it allows us to look across pathogen species, how this network of populations responds to them.
33:16 DD: My last question is, and I always ask this, which is what's your take-home message, what would you like everyone listening today to think about or know about, not TB necessarily in wildlife, but just wildlife diseases in general.
33:35 DJ: Yeah, so wildlife diseases in general... Well, what we found time and again, in different ways, in different contexts, is that they're really incredibly multifactorial. So here, we've tried to look at host genetic aspects of disease susceptibility, but we can't really look at that in isolation from the whole range of infections that these animals are exposed to, a gene that's great in fighting TB might be awful for some other infection. And we also can't think of it in isolation from environmental variation that imposes nutritional stresses, and also changes animal contact patterns over time. And so, in different contexts, different solutions have worked for animals across the evolutionary history, and so when we take a very focused lens on a particular disease in particular circumstances and manage for that, we run the risk of doing damage to the population in its ability to evolve and protect itself from future infections potentially. So, I suppose taking both short-term and long-term views and trying to incorporate them in management decisions is what comes out of this work, and just really trying to avoid the impression that we know it all and should therefore go and intervene strongly right away necessarily.
35:16 DD: Well, that is really interesting, and thanks again, Anna, for sharing your research with us and we'll keep our ears open for more stuff from your group. It's always really fun to read the papers that come out of your lab because they're really, just really, really interesting and cool. And thanks for joining us today and telling us about this issue. I think tuberculosis is really interesting in wildlife, and again, for sharing your information because I think before I went to vet school, I had no idea tuberculosis was in wildlife even as an animal science major. I learned about it in cows and TB testing in milk-producing cows, and that's about it. So thanks for sharing that. And that does it for this episode of Fresh Scoop and once again, we thank Dr. Anna Jolles for joining us today. So thanks Anna.
36:13 DJ: Thanks for having me, Kelly. It's a real pleasure.
36:17 DD: And we'll be back with another episode next month that we hope you'll find just as informative, and as we know, 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 Play Music, and Stitcher. And if you like today's episode, we'd sure appreciate it if you could take a moment to rate us because that will help others find our podcast. And of course, to learn more about Morris Animal Foundation's work, 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. And I'm Dr. Kelly Diehl, and we'll talk soon.