Curious Conversations, a Research Podcast

Travis (00:04)

What you know about the New World Screwworm? If you just answered, not very much, but it sure does sound like something that could eat my flesh, you'd be correct. There's been a resurgency of this flesh-eating larva in the United States recently, and nobody really knows why. But thankfully, Virginia Tech's Louise Escobar is an expert in exactly these types of creepy critters.

Luis E Escobar (00:24)

I have a daughter, and when I explain monsters in a forest, I use the new world screw worm. the damage it can cause to the single individual is terrible. and also the impact to the economy can infect can affect the the agriculture, pets, and public health. So you have everything in one.

Travis (00:45)

Luis is an associate professor in the College of Natural Resources and Environment at Virginia Tech. He's also a member of the Pandemic Prediction and Prevention Destination Area, the Invasive Species Collaborative, and Fraylin Life Sciences Institute's Center for Zonotic and Arthropod-borne pathogens. So his research really does focus on these kinds of creepy critters. And he goes into some detail as to why he believes this one may be the creepiest. I'm Travis Williams, and this is Virginia Techs. Curious Conversations.

Travis (01:19)

I hear the names of a lot of different insects and bugs, and they immediately give me a feeling. There's a feeling I get when someone talks about a ladybug and it's not a scary feeling. But when I heard about the screw worm, I did not get the same feeling as a ladybug because I don't know anything about a screw worm, but it it sounded scary.

So I wanna start the conversation simply. What what is a screw worm?

Luis E Escobar (01:41)

that's a fair question on fear, I think. the the Latin name actually is even is more scary. It's the man-eater. That's the meaning of the scientific name. So this is not a worm. Worms are those like animals that don't have legs and And are have that shape for their entire life. In this case, we have metamorphosis, which means it's a larvae at some point and then becomes another another kind of a different structure of animal. For example, a caterpillar is a larvae of a butterfly. In this case, we have a larvae of a fly, and that's but we name it a worm, screw worm, because It goes into the into the flesh of the infested animals. And in Spanish, we it's also we also don't refer it to a larvae, we refer it to a to a worm. So that's very interesting to me. I have no idea why we began with with the with this assignation of the term of worm. but something that is scary of this is specific insect is that there are not many insects that can kill directly the the host the animal that is infested so you can see for example a tiny fly with a tiny larvae and their kids right that are able to kill humans kill cattle kill horses so how this tiny animal has that superpower that being so making so much damage

Travis (03:24)

Wow. And so they were, if I heard you correctly, the other name for them is the man eater.

Luis E Escobar (03:29)

Flesh, many there, yeah.

Travis (03:30)

Fle the flesh eater.

Luis E Escobar (03:32)

It's human. Borax is that eats its humans, yes. And that's because there were some reports, like mainly anecdotal reports in the literature, health literature, agricultural literature that were referring to to these worm like infestations, killing humans or infesting humans and animals. But the official description of the species came from larvae that were killing people in an island in the Caribbean. So that's why the person, the entomologist that made the description, the the the the I guess it was a physician or entomologist. I think it was an entomologist who made the full description of the fly because it had an adult and a larvae and was assigning the name of the human eater because the samples came from deceased humans that were in a prison and were infested at that time.

Travis (04:34)

Wow, wow, I feel like you're right. They they did go with the less scary of the names then with Screwworm but it's still still pretty scary. So they eat flesh. I'm assuming because you know, you we have talked about you just mentioned that they can kill people, they can kill livestock. I'm assuming they eat the flesh of living creatures almost like I don't know, like a zombie.

Luis E Escobar (04:56)

Yeah, I guess that yes and no for something that makes this species very special is that when everybody is trying to identify their niche, some say okay, I'm going to eat poop. Some butterflies say, okay, poop is already taken, I'm going to eat the flesh. and these ones say, okay.

I'm I don't want to compete, I'm going to eat live flesh, hum humans that are alive or animals that are alive. so they have this specific niche and they don't need to compete with others. there is another another screw worm in the old world, Asia, Mediterranean, Africa. That's why we call this one the New World screw worm. And we there are other ones that are also larvae that eat flesh of living animals. But these two are important because they are very aggressive in terms of how fast they can infest, how many animals they can infest, and that's what makes them of concern for agriculture and public health.

Travis (06:03)

are we seeing them attack more humans or is it more that they target livestock?

Luis E Escobar (06:03)

Is it right?

I would say that I have not seen studies of diet preferences. Like, okay, you have all these animals, pick the one that you really, really, really like. But in general, yeah.

Travis (06:21)

Yeah, what tastes better to the screwworm? Me or the cow?

Luis E Escobar (06:25)

I think that the bias that we have is that we see that they prefer large body animals, but that's I think speculation on my side.

Something that we see is that when there are no available wildlife or or or animals, they may become obligated to infest people. But people are more like able to to scare them or or kill them, right? So they are going to try to attack humans that don't have that capacity, like babies or or more senior citizens or or people with disabilities. We have seen Guatemala, I'm originally from Guatemala, cases on the umbilical cord of babies, for example. So that's why I guess that diet preference may be related to the size of the animal or the capacity of the animal to to allow the infestation. a cow may be more easy to infest and a rodent or an animal that is better to clean themselves. I don't know here in the US we saw in in the previous epidemic that the species was able to kill 40-80 percent of pounds, mainly the the juvenile of deer. So there is age preference, there is definitely species preference, but why exactly you are going to see some hypothesis, but we don't we don't know for sure.

Travis (07:55)

Yeah. Well, my very non scientific hypothesis is that we generally wear more clothes than animals. and maybe that helps. except animals and cartoons, but they aren't real. But but for the most

Luis E Escobar (08:05)

Well,

Travis (08:07)

part, that's that, you know, I have less exposed flesh is my my ongoing hypothesis. well you mentioned that some of these ha attacks or infestations had occurred in I think Guatemala.

Where primarily is the New World screwworm at right now? And I guess is it on the move?

Luis E Escobar (08:28)

I think that what we see is not that this is an invasion, this is reclaim, like okay, it's it's claiming back its territory. So it the native range is where it's happening now. all records mention even Southern Canada cases, cases in in in the US already.

So it's areas where it's happening in most of the parts, we're not surprised. What is making this different is that is according to anecdotal records, because I have been talking with people that were handling the infestations before the eradication in the 60s, 70s, 90s, depending on the country, and they are now working again on the same pest.

And they say that something that they see different is number one, that it's affecting areas in higher elevations where they didn't see it before. And that could be because areas are warmer now, so the the flight can reach those areas because it prefers warm climates, tropical climates, or maybe it's because it's becoming it's adapting to those cold temperatures. So we don't we don't know, but that's To what people in the field are saying. They also say that in the past they used to see one or two wounds in the infested animals. And also that they saw infestations mainly in cattle. Now they say that the species is more aggressive, like infesting more wounds. It doesn't need a wound, to be honest. It's infesting mucosas like nasal mucosas. vaginas of animals, E and ice, for example, so it's only a place where it can enter and make like a like the screw, right? Like like able to to make a hole and and eat. And also they see and we we actually have data to support that claim that is becoming less peaky in the menu.

So it's not only focusing on cattle, now we see dogs, for example. we see dogs as the most infested species, at least in Guatemala. And here in the US, we already have cases in horses, a horse, a goat, sheep, dog, cattle, and a human, but that came from from a trip from in Central America.

Travis (11:06)

Wow. So how did we do we know how we eradicated them back, I think, in the sixties from the United States?

Luis E Escobar (11:14)

Yeah, I think that that's one of the main successes in in agriculture. I think like it's in the textbooks, in how to do science right and collaborate. And everything came from basic science, trying to see the behavior, how the how the fly behaves, their preferences, what they like, what they don't like. And something they found is that.

The females tend to mate only once in their lives. That means that they mate with the with a male and they store the sperma. So then later they can be laying eggs in different hatches like different times, but using the same from the same mating event. So that was a Key feature in their in their weakness. And that allowed to propose this idea that maybe having sterile males could generate females that are going to be producing eggs, but those eggs are not going to produce any flies. So that was the success we have been trying to use that technique actually for other species like mosquitoes killing people too, or or other flies that are affecting fruits. But the success in this case has been because they made only once. also something that I hear in the field, and and again, this is this is also speculation. We don't have data to prove that, but we want to hear the people that are in the front line. They say that maybe the the the the The populations of the fly now may offer some differences than the populations in the past, and we need to be prepared for that. So that's why we need basic science to see the preferences in diet, as you were mentioning, how much they fly. Maybe because we have clothes, we we are at less risk, and maybe that means we should focus on the tip of hair or the color of hair. Are there any differences in the animals infested? So we really need more research because most of the literature, when you are reading a review that is published just recently, they go back to the to the basics, the original studies decades ago. Yeah.

Travis (13:38)

Yeah, and it sounds like that this thing may have changed quite a bit since then. I'm I'm curious about so much about this this insect is one, I'm curious, how does it how does it move? How does it get around? Can it fly? Does it crawl? how does it move sp especially, you know, and you're talking about moving like into continents and stuff.

Luis E Escobar (13:58)

Yeah, it flies when it's an adult, but not a lot to sh to explain the speed of the current infestation. So that's why we believe there was something behind. So the fly, if there is no food, could move 10-20 kilometers. but we know that there is full, so it's a f it tends to infest in pockets, not like white sparks, but but some like hot spots, right? Wh where there is food, where there are prey, livestock or or or other kind of animals. so it it's rare in the wild, to be honest. It's not like you're you're in in a place that is like in like a cloud of flies. So they believe I have seen many potential explanations, and that's something we want to test. some believe that maybe climate variation made conditions that before were inhospitable, now they may be more suitable, so it was able to cross in areas of South America. others believe that maybe the mass migration of people from South America, maybe Venezuela to Central America, broke that barrier in the Darien that is jungle, and now we see them moving with their pets, for example, and maybe that facilitated the move of the fly. Others consider that the illegal trade of cattle was part of why we see this large and fast movement of the fly. and maybe it's a combination of everything. So at this time. is is based on hypothesis. We don't we don't we don't have solid data to support any of these claims or a combination of all of them.

Travis (15:45)

Well when when a screw worm when it does kill like a a cow, for example, how is it actually killing them? Is it I I'm assuming 'cause they're small and I could be wrong that they're not eating the entire cow. but is the cow the inf is it an infection that it ends up causing in the cow or is there something else that that it does to to kill the cow?

Luis E Escobar (16:05)

in general, I would say that the larvae don't want to kill the cow. They need the animal to be alive. If the animal dies, they die. So it should be there, they they try to manage this this trade-off between okay, I need to eat, but I don't need to eat too much, so I don't kill my my supplier. and that's why maybe big animals are able to tolerate higher infestations because The the wounds produce this smell that attracts other flies. It's like I don't know, when I was moving here to Blacksburg, I saw in this these reports of the that this was a very safe city, nice outdoors. My colleagues were saying that this was a nice place to work, so okay, I'm going to move there. In the case of flies, it's the same, but with chemical ecology. So they're releasing these smells, these volatile volatile components. So other flies can say, it's safe there. Others are having their babies there. And then have an and you have these wounds with larvae from different flies at different stages, different ages. And that's why we have wounds that never heal. They're always fluff, unless we we do treatment and that is a big cost for the animal, and that could be part of why they could die also if they damage some some organs that are more sensitive, and definitely secondary infections that could be play a role in if we don't if animals are not treated. And when flies don't have many hosts available, like if there is an island or or a place that is as isolated and there is no more farms around, they may tend to be more aggressive in festing a single animal or or or a or a farm for it. Yeah. Yeah.

Travis (18:01)

Wow. So they just it's like they just put up a sign to all their f fellow screw worms, the this restaurant is open. Come stay. wow, that's I mean kind of funny, but also terrifying. well I know you got a project recently as a part of a US well part of a series of projects from the USDA. what are you aiming to try to learn about the screw worm through that project?

Luis E Escobar (18:24)

Yeah, we have this grant as part of a challenge to study and understand better the new world screwworm supported by the US Department of Agriculture. And what we're trying to do is update our knowledge and fill some gaps and build in what has been done because we are building on on something and very very solid science. So we want to push it a little bit more on for example for for for example understanding if this humanitarian humanitarian crisis crisis have been playing a role in the spread illegal trade of animals or how the farmers behave or how they treat the the wounds are they treating and detecting the wounds or not so we want to have a strong human dimension to understand why the the spread has been successful why now so that's why we're going to be in the ground with mud in the boots understanding that dimension in Guatemala and also in Texas we're going to be talking with with the farmers there also we want to understand the genetics of the fly like the population structure the ancestry and that's going to Help us understand if we are able to control an outbreak and then we have another Obreak. Is this because the flag was there and hiding, or is this just a new invasion? We also want to understand the speed of the spread, the the like the corridors that the flag may be using, because maybe we understand what their landscape preferences are. We can block it better, we can identify, huh, here is where we need to be ready to to stop it if it comes. And also we want to see if there are actually some changes. We are hearing this more aggressive towards other species of animals, higher elevations being affected, what else? even I I I was told in the field that mm they feel that it's the the sterile males are not working as effective as in the past. so i is the are the wild females being more picky or detecting differentiating b between the wild and the sterile males? Everything is speculation. So we really want to add data to that to support the claims and say, hey, we found something that is all here. We should indicate a little bit more.

And finally, one of the parts is trying to do an attractant, allure, that means it's going to replicate the smell of a wound that is super good restaurant for the adult flies and see hey we can we can detect them faster and better if we use this attractant because the ones that we have now are maybe more expensive, they are still good or very may maybe they are hard to find. So we are just trying to build alternatives for the farmers. Here we focus a lot on the farmer and also a animal welfare for pets and public health. That's that's why we are doing these these studies. Really look at them.

Travis (21:38)

Well, you have quite the mystery on your hands, I think. and I'm really excited to to hear about all the things that you you learn from this project and I know that you are this is one of many different projects that you've I guess worked on with different types of animals and and insects and bugs. Every time I hear about your name, you're working about something that I feel like is creepy. So I'm curious on on in your scale, however you scale the creepiness of these things, where's where's the screw worm ranks far as I don't know, maybe in your top five or six creepy creepy animals that you've studied

Luis E Escobar (22:17)

I I have worked with a lot with rabis that makes people and animals behave like zombies, like they change the behavior. I have seen cases where animals like Labrador retrievers, super docile dogs become aggressive like like rabid animals, right? Because the virus changes that in the in the brain so through bites the virus can perpetuate more so but we have a vaccine we have a vaccine for that and we understand very well this virus to the point that we know how to stop an over i also work with hantavirus that is in my opinion a pandemic threat so another covet and we don't want that however the only Pathogen that also makes me have a chicken skin is the new word screw worm. I have a daughter, and when I explain monsters in a forest, I use the new world screw worm. Is the the damage it can cause to the single individual is is terrible. So it's a very miserable form of death. and also the impact to the economy can infect can affect the the agriculture, pets, and public health. So you have everything in one. And I was a bit surprised that we we are so concerned because you can see the prices in in beef now. The beef is changing in prices. And if you read a little bit more you can see that huh, it has some linkages to the New World screwworm. So it it this tiny you fly Is actually influencing the economy of a nation. But when we go and we see the amount of research on it, the num for example, I don't know, number of articles or sequences available to do genetic analysis or things like that, you see, huh? We were underprepared. We we are just trying to catch catching up now,

Travis (24:22)

very I well, I'm very thankful that you're on the case of helping us catch up because it sounds very terrifying. Possibly also though a a a nice Halloween costume if somebody's still out there shopping for one of those.

Luis E Escobar (24:26)

Yes, yes, I I think that this this podcast is very timely for Halloween because if there is some monster it doesn't have hair and it's not big, it's tiny and comes from