Wiggly Worms

Dr Narelle Dybing with Dr Tom Carruthers

Episode #2

Do parasites like hookworms and tapeworms make you squirm? Dissecting foxes and analysing parasite infections sounds gory, but Dr Narelle Dybing’s work is incredibly important for public health.

We caught up with the Murdoch University research associate to get the nitty-gritty on parasite infections. Over an English Breakfast tea, Narelle shares how her research is helping stop parasites in urban foxes spreading to pets (and humans!).

Narelle also has a few glass specimen jars up her sleeve, so take a peek at some parasites and find out how we can reduce the risks of infection.


Narelle completed her PhD in 2017 on feral cat and black rat parasites on Christmas Island, Dirk Hartog Island and southwest WA. Since then, Narelle has been involved in many projects investigating invasive animals and the parasites they carry including urban red foxes and wild dogs in Northern WA.

You can find out more about Narelle by checking out her group website, and follow her on Twitter (@NarelleDybing).

2021 Narelle Dybing



Dr Tom Carruthers: Goopy stuff is what you kind of deal with in the lab.

Dr Narelle Dybing: Yeah, I can deal with anything now, I think. I can work anywhere!

Tom: G'day and welcome to another Mug of Science. It's part of Pint of Science Australia, online this year for 2021. My name is Tom Carruthers and I'm here in Applecross, which is part of...near Perth, something like that! It's in Western Australia. I've got the immense pleasure of being able to have a chat with Narelle Dybing, who is a postdoctoral researcher at Murdoch University. We're here to have a bit about a bit of a chat about parasites.

Narelle: Yes, that's correct.

Tom: This is going to be a fun little chat as part of Mug of Science! So first of all, the first question we need to start off with is what's in your mug today?

Narelle: So I don't drink coffee. So I've got an English Breakfast tea. So I usually drink that or hot chocolate if I go have a coffee with someone.

Tom: So let's, before we get into the nitty-gritty of creepy crawlies that live on other things, let's talk a little bit about you. When you're not in academic science mode, what do you do to keep yourself busy? What do you do to interest yourself?

Narelle: Well I have a couple of dogs, so two Jack Russells, and so I like taking them out and going to cafes, going to parks and having little dates with all my friends that have dogs as well. I also do a bit of photography as well, so I like nature photography and also doing some for friends that have babies and families and kids and parties and stuff like that.

Tom: Right, yeah fantastic. A little birdie did tell me that you might also enjoy making wheelbarrows, is that right?
Narelle: I like helping out around the house when we have to put things together. I actually really love IKEA furniture and things like that. I actually really love putting things together. Maybe I should have been an engineer or something, but yes I do love helping put things together.

Tom: And you did just come to this interview after making a wheelbarrow? Yes, hi Dad, I'm just waving in case you're... well, of course you're watching, what are you talking about. So let's talk a little bit about how you got into science. So that's actually quite interesting, I'm glad that I went down that little bit of a diversion in terms of you liking putting things together as well as you taking photographs of the natural world or whatever that, seems to start to imply to me a kind of an observer and fixer, kind of role. Was there something, were you always passionate about science? Was it something you were always going to go into?

Narelle: Yes, I've always loved science, but the type of science has always changed. So for a while I wanted to be a geologist and then a marine biologist, and you know, and then I was going to actually go into cancer research, because my grandmother passed away from cancer a while ago and just recently my uncle passed away from cancer as well. But it's just one of those things that you know the progression got me to parasites because I did do one of the units at university and I realised just how much I loved it and I was just intrigued at how something so little can do something so crazy and so big which everyone can kind of see from COVID, you know from things being introduced from animals into a human population, just how crazy it can get. So I like being able to see how things work and you know, how something can affect something else so much.

Tom: So yeah, I'm interested by where your interests were, because you were starting to talk about like, you know marine biology and then cancer research and you've ended up in parasitology and whatever. These are all kind of like within the biological sector and then you're like in geology, is there a reason why you then decided to not go and study rocks and things that happened in the ground?

Narelle: Well I think it was more of a natural world thing that I really enjoyed. And you know we would go on you know at school, you'd go on little excursions and stuff like that and I think that's where I was like oh this might be something I could like and it didn't really last too long but it's definitely been more a biology natural world thing, and then humans and animals and how diseases can affect you know, animals and humans.

Tom: You did your undergraduate at Murdoch in...

Narelle: I actually did a double degree in Conservation Biology and Biomedical Science.

Tom: Cool, so you were still keeping that cancer thing open at the time. Yeah, but you were like, this is what I'm really interested in, but this is where I think I might be going, was there anything in particular in Biomed like through that undergrad that really excited you or that was really interesting?

Narelle: Actually pharmacology and chemotherapy was a very interesting unit that we did, just again because I started working at a pharmacy at about the same time, so it was really interesting to see how these things interacted and who took what and for particular reasons and what they can't take, so it's really interesting to be able to say you know, these are the things we have these are the options you've got, we can help you some way or this is what research is going to be happening for particular diseases. I've got the animal side, the human side, and I can look at actually the health of both. So what I do is look at parasites in specific animals, but I'm also looking at what they can give to humans and what humans can give to them as well. So it uses both my degrees, which is really good.

Tom: Yeah, you then moved into a PhD?

Narelle: I did Honours first and then a PhD.

Tom: In the same kind of space or slightly different?

Narelle: Yeah, so my Honours was in red fox parasites and feral cat parasites in the southwest.

Tom: Southwest of...?

Narelle: WA. Yep in the Wheat Belt region. And then I did my PhD in feral cat parasites and black rat parasites on Christmas Island, Dirk Hartog Island and around the southwest of WA as well. The problem is we don't necessarily know in what prevalence or what percentage of the population would be infected with this particular parasite, because different areas won't always have the same parasites but the host can be susceptible to those parasites so we want to see in what area they have particular parasites and therefore what other animals or humans can be infected or affected in that area with those particular parasites.

Tom: Right, okay so the selfish human interest aspect, here, being aware of what kind of threats or organisms that are around in a particular space.

Narelle: Exactly, and therefore we can help to manage or we can help to think about control measures, whether it's in invasive animals. So whether we need to target a specific area more for these management processes or if there are ways in which we can actually stop, whether we need to make sure we're washing our washing our food properly and cooking our food properly, or you know if it's particular hygiene procedures that we need to pick up on in certain areas in particular or. And so really, the key here is it's not necessarily that they're an introduced species, but it's that that particular species is more likely to roam a little bit and not necessarily be locked into a single location, and so there's the potential risk of that that human animal barrier starting to touch, right? And one big thing as well that we're trying to think about at the moment is the fact that what we're focusing on is pets as well. So pretty much anything that, so for example I'm looking at urban red foxes at the moment. So around here in areas that there's a really high interface between humans and wildlife, but we're trying to take out pets, as you can see there are dogs everywhere, and they pick things up off the ground. So wildlife, pets and humans.

Tom: Exactly, so the pet can become the vector as well.

Narelle: Exactly and our pets can get sick, and we don't want that either, yes, you know so but we know that foxes and feral cats will carry the exact same parasites that our dogs can get and our pet cats can get as well, so there's this big cycle and I think people do kind of forget, that there is this big thing in the environment that we need to be aware of.

Tom: Yeah, we hang out in the same place where these other animals are, and so therefore increases the risk of us being exposed to those parasites.

Narelle: Exactly, and given like Perth has, I don't know if you've noticed how just wide spreading Perth is, and it's just getting longer and longer, and we're now getting into areas and building houses in areas that used to be either national parks or areas where there's at least there's a lot of wildlife living in those regions, so we're actually now branching into these areas and so there is a bigger risk as well in those areas either transmitting to you or the pets as well.

Tom: Right, that that obviously will then have an impact in terms of not only us expanding, but also climate changing, which therefore means that that animals are shifting their habitats to find the climate that makes more sense for them.

Narelle: Right, absolutely yeah and then we've also got you know, land clearing and everything like this, so everything is moving artificially whether it's humans and then they've got this climate change as well, so all these populations are spreading and moving into areas they weren't before.

Tom: Yeah, right. Very cool, okay well, not cool, but I think I'm understanding. So is your work focused on those species that have these parasites or do you particularly focus on a particular parasite that happens to be in those species?
Narelle: So at the moment I'm focusing on a particular invasive animal. So we're looking at the urban red foxes, but one parasite that we have found which is actually very interesting and can be quite significant is heartworm. So obviously everyone, well most people, are trying to worm yearly or monthly for heartworm, and it's one of those parasites that...

Tom: Worm themselves?

Narelle: The pets.

Tom: Sorry yeah, I was just having a panic of, oh hang on, maybe should I be worming myself at home each year!

Narelle: No sorry, worming your pets yearly.

Tom: Come to Perth, it's scary here! They've got parasites that get you. They're everywhere.

Narelle: But the question is whether it was in WA. Right, so we know it's over east, but in WA we don't see it very often in pets. And so we also know that red foxes can carry this parasite, so we wanted to see if it was in what we call a reservoir host, so meaning they can live in the foxes and foxes can therefore also... So the foxes themselves don't transmit this parasite to our pets, but it's transmitted by mosquitoes.

Tom: Okay so yeah, let me run this through. You got little foxy who's going along, they picked up a parasite.

Narelle: Mosquitoes give it to them.

Tom: The mosquito gives them the parasite, the fox then is not too damaged or hurt by them?

Narelle: They can get affected the same way dogs can. But when it comes to this parasite, it really depends on the severity of infection as well. So sometimes they can have that many worms in their arteries, so it's called heartworm, but it lives in their pulmonary artery a lot and so it can actually block the arteries itself. So they can then have cardiac effects. Yeah or once we try and actually treat the pet for it, actually is when the more most damage happens, so preventative is always better than trying to treat the animal when it comes to this kind of parasite.

Tom: That's because the parasite themselves can then get into the bloodstream instead of holding onto the side?
Narelle: Yeah and it can block other blood vessels.

Tom: And so it's effectively like a little blood clot and so you're effectively creating blood clots inside there.

Narelle: Yeah very similar. Right so we always recommend preventative treatment as opposed to treating them and I think everyone can you know agree that prevention is always better.

Tom: It's cheaper and easier and all that kind of stuff.

Narelle: Yeah, because we want to keep those dogs happy and healthy.

Tom: Yeah all right so okay, so fox can pick up this parasite from mosquito. Now parasite's inside fox, yeah, fox goes about doing its thing and this is where the reservoir aspect comes by, because you've then got this population of foxes who are not getting that yearly treatment. They're just hanging out over there behind that fence, yeah, and then there are mosquitoes especially if there happens to be some sort of event that creates a big flush of additional mosquitoes around, they bite or suck the blood of the foxes, they come along and they're like, actually I'm hungry for a bit of dog as well or whatever, and then they can pass on the parasite to the dog, or they can pass it on to humans...?
Narelle: Humans actually can get infected by this parasite , but it's quite rare for that to happen but there is a potential for it to happen, but it doesn't really do too much in us, but again it's very rare.

Tom: Is it just because we're a bigger organism?

Narelle: Well because we're not the suited host, so therefore it doesn't want to live on us.

Tom: Yeah because the parasites like they want to live in the space that makes sense for them, and so doggy veins are a little bit more comfortable than human veins for them.

Narelle: Yeah, in this case, yeah that's it. Right it's a complicated thing but at the same time the parasites have found just a way to be able to do it so efficiently.

Tom: Which is going to happen and that's like the whole tenet behind evolutionary pressure or like those kinds of concepts...

Narelle: Exactly, finding new hosts that they can live in in an area where they didn't think they might have been able to.

Tom: And it's not because they're choosing that host, it's just that if they don't, they affect everything, if they die, they die, if there is any chance of them surviving then they can survive if they do it often enough. And it means that you're more likely to as a population survive and if we wipe out one arm of that, If somehow we were able to say okay no mosquitoes the next three years please and that was somehow able to magically happen, there's a chance that there would be another vector that just happens to be found, that becomes...

Narelle: Yeah it could do, and that's the thing like we just and this is why the problem with introducing animals to different areas is such an issue. We don't know what they have and what they can pass to other wildlife, they don't know what they have that also could then, you know, find another host to survive in in different areas and this is what's happened, you know, when foxes and cats have come to this area that they weren't in before and you know, because they don't have the same wildlife in Europe to what we do. Some will be the same but not every bird is going to be the same too. Not every little mammal is going to be the same.

Tom: Let's talk about your actual day. So if you're actually doing research, if you're going to work next week, yeah, what is it that you're actually doing as part of this problem? Are you doing the surveys of the animals, are you looking at these parasites under a microscope? What's the nitty-gritty?

Narelle: Pretty much all of the above. So what I do at the moment, so we're working with contractors around Perth, which are hired by city councils to help manage you know, foxes in reserves or things like that. We're also working with Peel Harvey Biosecurity Group now, so we're going to expand further south into these newer residential areas as well, so we will get them either from these private contractors or landowners that have to manage these on their properties. We'll pick up the whole animal, so we'll get a whole fox for example. What we try and do is get them to put them in a bag individually, because they've got fleas and stuff on them, and if you don't put them straight in the bag they jump ship. So what I do is I comb every inch of the animal. I look for lice, I look for ticks, I look for fleas. If the fleas are alive, they'll jump around everywhere, and I count them as well and then I necropsy the entire animal, so I look inside the animal, in the heart, in the lungs, in the gastrointestinal tract, in the liver, everything. I take some tissue samples, look for parasites, and then the gastrointestinal tract, I actually look at under a microscope and also obviously I count the individual worms again, and we're trying to figure out just how many these hosts can actually deal with, look at body condition of the animals. See if they're healthy or not. Yeah and then we can also do some DNA on some of these tissues, because some of them are blood parasites, so we might look in the spleen or in the blood itself, and we look for DNA of particular parasites, or even bacteria, sometimes we go into. Yeah and then we also do SNAP tests, they're called. So SNAP tests are the tests that vets will use to test for heartworm and things like that, and other bacterial...

Tom: And those SNAP tests are looking for it's like kind of similar to a test that we might get with a blood test, where it's looking for a signal that could imply that there is...

Narelle: Yeah so they look for antibodies or antigens, so see whether we've been infected or if we have any antibodies to it or if there's any antigens in there in the bloodstream of that particular parasite.

Tom: Yeah okay, so goopy stuff is what you kind of deal with in the lab.

Narelle: Yeah. Yeah, I can deal with anything now, I think I can work anywhere.

Tom: Wow. You count the worms. What is the kind of load that that a fox could kind of like carry, of these creepy crawlies on the inside?

Narelle: So it depends on the parasite itself. I've actually got some here I can show you in a little bit. But there are some tapeworms that can be over a metre long in them, so they can have up to like 15 of those in their gastrointestinal tract.

Tom: 15 of those?

Narelle: Yeah sometimes a lot more than that.

Tom: A metre long? The fox is only this big, right?
Narelle: The gastrointestinal tract goes around and then the worms can double up in there... Yep and then there are some little ones...

Tom: Does it cause pain?

Narelle: Sometimes if it blocks, it can cause blockages so the food doesn't always go through properly or something like that. So again, it depends on the amount, but usually because foxes are the main host, they don't want to kill the fox or the main host.

Tom: That would be a bad idea, you don't want to burn down your own house.

Narelle: Exactly, that's exactly it, you want to be able to continue on your life cycle so usually...

Tom: …and if you need to burn down your house for your kids to be able to have a new house, then sometimes you might do that, right?

Narelle: Yeah, that's it.

Tom: But the tapeworm can live for a very long time relatively, kind of?

Narelle: It depends on the species, because there are hundreds of different species of tapeworms, and in a fox alone there's oh, I don't know, there's over 20 different species that can live inside a fox, depending on the region as well that they're living in. So yeah there's quite a lot. Yeah and then there are some called hookworms, which are actually only about half a centimetre long, and I found some that had over well over 200 of those within their gastrointestinal tract. And they ingest blood meals from within the gastrointestinal tract. So they attach to the mucosa of the intestine yeah and they ingest blood. So some of them, depending on what species, can actually cause anaemia in certain animals if there's a lot of them.

Tom: Right so, if you have heaps of these hookworms, then because they're eating all of your blood, yeah, you don't have any blood left for you to be able to do your own thing, right.

Narelle: Exactly. So sometimes parasites obviously will get greedy and then they can make the main host sick, if there's a lot of them. Because they're not consciously trying to do anything they're effectively, they just want to survive, little biological machines that are doing their thing.

Tom: Yeah and if they happen to succeed too much, they can boom and then bust, right.

Narelle: That happens as well. Exactly, and then if, you know, the fox for example will continuously eat the same thing over and over again, and that population of, for example you know, a bird, so some of these parasites are carried by birds, if they continuously eat birds and all of these birds are infected with that same parasite, the fox is going to continuously, overloading, yes, so it really just depends and sometimes foxes like individuals will actually have a preference for what they eat, as well and so.

Tom: That makes sense. You prefer energy drinks and I prefer cappuccinos. Yeah, that's fair. Yeah, I'm sure if I was a fox I'd have a preference for something. Yeah, wow. So do you know if humans have got this many parasites normally?

Narelle: We carry a lot of parasites, but that's why we obviously we again, we advocate for washing your lettuce, for example, properly or something from your garden, washing your food properly before it gets eaten, cooking meat usually at least to about medium would be good, and storing food properly as well like in fridges and freezers properly.

Tom: And I mean the washing thing to me makes sense, that's you physically removing any of the parasites or other wormy bits or things like that or eggs The cooking makes sense as well because you're killing any that are left over, that are on the surface or inside somewhere, yeah but then the storage thing is just, that's reducing the load isn't it? That just stops them from growing as much?

Narelle: Yeah so if you, for example, have to you have to put them in a freezer for a certain amount of time as well, so it will actually inactivate if there's something in there. So it needs to be stored properly at a certain temperature usually, in order to kill that parasite so it can't be infected.

Tom: So just keeping something in the fridge because it was cold doesn't necessarily...

Narelle: It depends on what it is. There are some parasites, for example, there's one called Toxocara canus and Toxocara cati, so they're roundworms. Do you want me to show you a jar by the way?

Tom: Yeah, show me your jar.

Narelle: All right, so these guys are Toxocara.

Tom: Ooh, they're goopy.

Narelle: Yeah so these ones, the main host is the dog or the cat, depending which species it is, the eggs come out in the poop, they'll use, for example, you know a playground or sandpit or the beach, yeah, the eggs can live in the environment for over 18 months.

Tom: Right, so it doesn't have like that one week window, yeah.

Narelle: Yeah, so it actually has a really long period of time where it can be effective and we can pick it up. So that's one of the ones where you've got to make sure you wash your hands and under your nails and kids eat dirt sometimes, so you've got to be aware. Obviously, you know, people say you need to expose yourself to them so you can fight it, but obviously to a certain extent, but you still don't want to be ingesting parasite eggs either. So every now and then a little bit of dirt is fine, but it's when kids go into a sandpit and you know, it becomes their thing that they're just doing lots and lots. Yeah and even just you know there's certain parasites that your dogs lick your face and stuff like that and so just reducing that you're still exposing yourself to your dogs, but don't let them lick your face which directly can introduce something to you.

Tom: Right. Is there anything else in this box you want to show me?

Narelle: Well there's quite a few. So this one is a tapeworm called the zipper worm or Spirometra. I'm not going to say the special name because it's very long. So this one is actually one that's quite bad for wildlife and for humans as well.

Tom: Oh wow it's flat, it's like that's why it's a tapeworm, yeah. Yeah okay, so I could see how you might be able to get several of those...

Narelle: So this is the one that I found that have been well over 75 centimetres long. And so these ones, the first intermediate host or that first juvenile stage actually has to live in a freshwater environment, so like a lake or river or something like that or a waterfall.

Tom: And a fox drinks some water...?

Narelle: Actually the small mammals or birds or reptiles or amphibians ingest the water, and then the foxes and cats and dogs actually get infected by eating those, but we can actually get sick by swimming in the water that has the parasite in the water. Yeah I think that actually happened not too long ago, there was someone that went swimming in a dam or something.

Tom: Which is something we can deal with with modern medicine anyway, right, so yeah in general a lot of these parasite issues, we've got a fairly okay handle on from a medicine perspective, don't we?

Narelle: Most of them, yes, some of them again, a lot of people might not notice it until you're quite sick, so really it just depends, so obviously we don't want to get to that point where we're quite sick and then treat it, we'd rather just avoid the situation.

Tom: Right, you've got another one of those?

Narelle: I've got a couple of things in here. So this is another tapeworm, which is Taenia. So cats get sick from this one by eating rodents, and foxes or dogs might get sick from eating offal from like the organs from sheep and cows and things like that, depending on what species it is, and there's a little one in here which are the little hookworms.

Tom: Oh they're itty bitty.

Narelle: Yeah, so when we get infected by these guys, which again can be from the beach or something like that, we actually get this rash on our arms, and it's actually called creeping eruption or visceral lava migrans, because it's on the skin and the larvae, because we're not a normal host, it just sits on the outside of our skin layer and just kind of causes this rash.

Tom: Because it doesn't well, have the mechanism to be able to do anything else, because we're just the wrong host.
Narelle: Yeah, exactly.

Tom: I think it's pretty clear, the answer to my second-last question, the positive impact or the impact, relevance, that we give to people and whatever, is that by understanding these things better, we're able to protect our health and protect the health of our animals, exactly, and that's the driving force behind everything you're doing.

Narelle: Exactly, we want to be able to educate people to know why it's so important, first of all to manage these invasive animals and also how to protect ourselves from these kind of parasites, and our pets from these parasites as well.

Tom: Cool, so just before we wrap up there's one last question that we do ask people as part of our Mug of Science and that is for you to finish off this sentence. The sentence is: to me, a scientist is someone who...

Narelle: …is passionate about helping animals and people.

Tom: Nice concise answer. I'm just noticing like the mic drop inflammatory statement that you've just made about, you know, any of the astrophysicists who may not be helping animals or... but here, you heard it first in Pint of Science, Mug of Science where parasitologists don't accept mathematicians into their definition of what scientists are!

Narelle: No I know! They help animals and people not by their health, they help by increasing their knowledge and mathematicians can help by doing a whole lot of things and so can astrophysicists, so it's all in their own way, they can help mankind, okay!

Tom: So I've been Tom Carruthers, this has been Mug of Science as part of Pint of Science online in 2021. Thank you so very much for taking the time to have a chat with me today, and for letting me dig at you a little bit about some of these creepy crawlies that live under the skin of some of our friendly dogs and foxes. You can catch Mug of Science all through Pint of Science this month and we hope to see you at another episode! I've been Tom, thank you very much.