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Melanie Cole (Host): The dangerous rat lungworm parasite is showing up in a growing number of species, including giant African snails and invasive Cuban treefrogs in Florida. What does this mean to human and animal health as well as to the environment? We're talking about threats to human, animal and environmental health posed by the rat lungworm parasite today.

Welcome to UF Vet Med Voice with the University of Florida College of Veterinary Medicine. I'm Melanie Cole. And joining me is Dr. Heather Walden. She's an Associate Professor of Parasitology in the Department of Comparative Diagnostic and Population Medicine at the UF College of Veterinary Medicine. Dr. Walden, thank you so much for joining us today. Can you tell us about this dangerous rat lungworm parasite that's showing up in a growing number of species? What is it and where is it being found?

Dr Heather Walden: Hello and thanks for having me. So the rat lungworm is also known as Angiostrongylus cantonensis. That's the scientific name and this parasite is naturally found in rats, various species of rats. And it infects the pulmonary arteries. And then, it also uses intermediate hosts, such as gastropods, so snails and slugs, different species of those to complete its life cycle. And the parasite itself can get into other hosts. As you mentioned, the giant Africans snail, which is a natural intermediate host for it, as well as the Cuban treefrog, which is what we call a paratenic host. So they pick up infectious stages of the parasite and then the parasite just hangs out in these hosts until that host is ingested by a vertebrate host, so the rat or some other what we call incidental hosts in that instance, something like a dog or something along those lines.

And then, when it gets into these incidental hosts, so humans fall into that group, dogs, horses, birds, a variety of other wildlife, that's where we start to see some of the disease associated with infection. And these are neurotrophic parasites. So when they get into these incidental hosts, the larval stage will actually migrate to the central nervous system and try to do some development as it would in a rat. But because it's not a rat, it can't complete its development. And so they get caught up in the central nervous system. And then, you start to see these neurologic effects of the dead or dying larvae, or just the migration of those larvae.

Melanie Cole (Host): Wow. So what are some of those neurological effects as you're speaking to us about what this means to human and animal health, as well as to the environment for that matter? Tell us about some of those complications or symptoms.

Dr Heather Walden: So the hallmark of infection with rat lungworm is known as angiostrongyliasis eosinophilic meningitis. And this can be also seen in not only a variety of our incidental hosts, but a lot of the animals that become infected. And if we're talking specifically about humans or dogs, so in humans, at least in adults, the most common symptom would be something like headache. And then, you could get intestinal upset because the larvae, when they're ingested, penetrate the intestine. You could see stuff like fever, paralysis, limb weakness, and things along those lines. In dogs, very similar that you would end up seeing, so the paralysis, some sensitivity, gait abnormality, muscle wasting. Sometimes you'll see urinary incontinence.

And this parasite can be very difficult to diagnose. And so sometimes you don't actually get a good answer when you're kind of running through your list of diagnostics, such as trying to pick up the parasite through PCR, so looking for the DNA in either blood or CSF or sometimes people try to find the parasite using imaging techniques, which aren't always useful. Sometimes ELISAs can help. But there's nothing that can give a definite answer a hundred percent of the time, unfortunately.

Melanie Cole (Host): That's so interesting. So then, for other vets, Dr. Walden, is clinical history what's most important? How do you make the determination and then speak about if you do make this determination in a dog or even in a human, then what's next? How is it treated?

Dr Heather Walden: So you're absolutely looking at history. So travel history, one. Has that animal or human gone to a place where this parasite's considered endemic? So it's been diagnosed in humans, at least in over 3000 cases of human infections across the world. And here in the United States, it's considered endemic in Hawaii where it's been for 40, 50, 60 years. We've also found it in a variety of states in the Southeastern US, throughout Florida, Louisiana, Texas, Alabama. There's been cases in Tennessee.

And so, you have to look at history, and then you also have to look at the lifestyle of that particular host. So have they been around those intermediate hosts, so the gastropods? Like dogs, for instance, they tend to play with those, ingest those, that type of thing. Or maybe they're going after some of these paratenic hosts. So we already know that the Cuban treefrog can harbor those parasites. It's very likely that other species of frogs, including potentially our native frogs, could harbor this parasite. Some of the anole lizards and things like that might actually be hosts. We don't know that yet.

Melanie Cole (Host): What about birds?

Dr Heather Walden: Birds are typically an incidental host. So they're going to end up in the same spectrum as dogs or humans. So the parasite, from what we've seen in some of the case reports in birds, it's not going to be harbored in that infective stage. And so it's going to keep going through its development, similar to what you would see in a dog or in a human. And so, those wouldn't serve from what we know of right now as a source of infection, like some of these other lizards or amphibians, crustaceans, fish, those kind of fall into that paratenic host group that might lead to a potential infection.

Melanie Cole (Host): I think I was just asking if you are seeing it in birds because they swallow these frogs, so they're going to be similar to dogs and humans. Have you been seeing it around in these various species?

Dr Heather Walden: There's only been one case report that we've seen in birds, and that was out of a bird in California. And I don't really know the history of that bird, where it came from or anything like that. and that was, I believe, a falcon. And so there is definitely that potential. But it's not something that's been reported. And just kind of thinking about what birds eat, just like you mentioned, there is that potential. When I'm seeing this parasite, it's been in the definitive host, so the rats and it's been in gastropods and then also, it has been in non-human primates, so the incidental hosts, and then, the Cuban treefrog. So those are the times when I've actually seen this parasite.

Melanie Cole (Host): Wow. So, Dr. Walden, you've been a source in the national media on the rat lungworm for several years as well, because people have died from this parasite or gotten super sick, yes? Speak about that for us.

Dr Heather Walden: There is definitely the potential for this parasite to cause death in its incidental hosts. In the non-human primates, one of those infections did result in death in that particular animal, and that was an orangutan. That was from the Miami area. And then, there have been human infections where you see death or severe disease, even coma. And all of that is dependent upon the numbers of larvae that are actually ingested.

And so with each intermediate host species, so all your different gastropod species, they have the ability to harbor a varying number of infectious larvae. So some may just harbor, you know, a few to maybe a few hundred, others can harbor thousands. And so there's a difference in the disease that when you ingest maybe a few of these larvae versus thousands of these larvae. And so that's, what's going to determine the severity in each individual host.

Melanie Cole (Host): This is so interesting and something that I'm not sure very many people know about. So as you wrap up, why is the parasites expanding presence concerning to human and animal health, as well as the environment? And please summarize for us what you'd like people to know about the dangers of the rat lungworm and how to minimize the chance of infection as well as how to protect our pets.

Dr Heather Walden: The parasite itself is one that I think with the changing climate and the warming climate, as these gastropods are able to inhabit areas further north, they're taking their, of course, parasites with them as are any of these species as they're moving more northward geographically. So you have that kind of push northward. Then, you also have the transport of just people moving everywhere, animals moving everywhere. Some of these hosts can hitch rides, so thinking of gastropods hitching rides on plants as they're moved to various places, or maybe the frog hitching rides on vehicles, RVs, things like that, and they're being moved to various places. And so the parasite is getting an opportunity to move with these hosts to different regions and then infect these different hosts. And so, oftentimes, we see it start with invasive hosts as they move through. And then, it spreads into our native populations. And so that's one concern that we have, is how the parasite may affect our native frog populations or our native gastropod populations and things like that. And then, also just that movement, spreading it to other parts of the us further north.

And so when you're thinking about minimizing the transmission to not only ourselves, but also our pets, there are a variety of things that you can do. One, just keeping an eye on your pet. Making sure that when they're outside, they're not playing with gastropods, trying to ingest gastropods, and then also, trying to make sure they're not ingesting some of these amphibians or reptiles. Because from a parasitology point of view, not only are these host potential hosts for rat lungworm, but there are a wide variety of other parasites that use these hosts that can infect your dogs or even your cats. And so making sure that you're doing your best to limit interactions with these particular hosts.

And if you are someone that ingests some of these hosts, making sure that they're properly cooked is really important. And that will help minimize the transmission to humans. Also, when we're thinking about transmission to humans, making sure young children they're playing with these animals, one, that that's limited; two, they're washing their hands, they're not ingesting them. There have been several accounts of rat lungworm infection in children or young people because it was a dare to eat a snail. And unfortunately, that snail was infected with rat lungworm. And so trying to minimize that is really important. Making sure if you're growing your own produce, that it's washed thoroughly. A lot of these snails are really small. And when you think of the folds in lettuce and things like that, they can get down in there. Sometimes just a piece of the snail is still left or a piece of the slug is still left and that's accidentally ingested. And so making sure that everything is properly washed.

There have been reports that the snails can actually fall into water and the drowned snail will admit their larvae into the water. And so, there's a period of time where those larvae can remain alive in that body of water. And so making sure that any water outside is covered. You're not allowing gastropods in there so that they can drown. If you do see that, dumping that water, washing that container out and starting over is really important. Because if you were to wash produce or anything like that or even wash your hands in that, there's the potential for the larvae to then be transmitted to the produce. And so you want to make sure you're limiting stuff like that.

Melanie Cole (Host): Wow. This was such an important and informative podcast. Dr. Walden, thank you so much for joining us today. And for more information, and to listen to more podcasts from the experts at the University of Florida College of Veterinary Medicine, please visit vetmed.ufl.edu/ufachievers. And that concludes today's episode of UF Vet Med Voice, brought to you by the University of Florida College of Veterinary Medicine, advancing animal, human and environmental health. I'm Melanie Cole.