News

From the Front Row: Mosquito surveillance and mosquito-borne diseases

Published on July 15, 2022

 

The following is a transcript of an episode of From the Front Row: Student Voices in Public Health, the University of Iowa College of Public Health’s student podcast. This episode features a discussion between College of Public Health students Radha Velamuri and Anya Morozov and Iowa State University Prof. Ryan Smith. This episode was published on July 15, 2022.

Radha Velamuri:
Hello, everyone, and welcome back to From the Front Row, brought to you by the University of Iowa College of Public Health. My name is Radha Velamuri, and I’m joined by Anya Morozov. If this is your first time with us, welcome. We’re a student-run podcast that talks about major issues in public health and how they are relevant to anyone, both in and out of the field of public health. We’re here today with Dr. Ryan Smith, an Associate Professor in the Department of Entomology at Iowa State. He oversees mosquito and tick surveillance across the state of Iowa and is here today to chat with us about his work and as the first guest in our series about vector-borne diseases. Welcome to the show, Ryan.

Ryan Smith:
Thanks, Radha. Thanks, Anya. It’s a pleasure.

Radha Velamuri:
Before we get to discussing your work, can you tell us a little bit more about yourself and your career path, how you ended up at Iowa State in the Department of Entomology, and what made you choose to willingly study bugs?

Ryan Smith:
Yeah. I’ll try to be, I guess, as succinct as possible, but I mean, I’ve been interested in mosquitoes especially for a little over 20 years now. It more or less started when I was an undergraduate just kind of finishing up my degree in biology. I was taking a class, and we had to talk about a recent advance. And one of the topics that one of my friends had mentioned was this idea of making transgenic mosquitoes, or kind of manipulating the DNA of a mosquito such that you can manipulate them so that they wouldn’t be able to transmit diseases anymore.

Ryan Smith:
This was an idea that really captivated me, and so I wrote up my project on this. I realized that they’re doing this, that there was actually a faculty member on the campus where I was doing my undergraduate degree. And I ended up applying for graduate school and joined his lab. I started off as a master’s student. During the process, I transitioned into a PhD and worked on making transgenic mosquitoes with the idea of, at least at the time, was to use transposable elements for gene drive, much like people have now adopted with CRISPR-Cas9 with this much newer and much more improved technology. So kind of with that, my interest in mosquitoes have continued.

Ryan Smith:
So following my PhD, I did a postdoc at Johns Hopkins University, and that’s really when I started to get involved more into infection and some of the diseases that mosquitoes transmit. And really the focus that I had there was on malaria. So I started looking at mosquito physiology and the immune system to understand how and why these mosquitoes can transmit these different diseases, especially one like malaria that has really large, devastating impacts throughout the world.

Ryan Smith:
Ultimately, after a period of time, I was on the job market and applied for a position here at Iowa State, and I ended up getting it. So I’ve continued some of that work as far as looking at malaria parasite infection. We’ve also expanded that into other viruses like Zika and dengue in the lab. But with my position, we have also… It’s always been affiliated with this oversight of mosquito surveillance for the state. So since I’ve joined here, I’ve kind of learned some new techniques and some new skills as we’ve tried to better understand mosquito abundance and its impacts on mosquito-borne disease, tick-borne disease in the state.

Anya Morozov:
Yeah. So some of the diseases you brought up, like dengue, Zika, malaria, those are usually what I think of when I think of mosquito surveillance. And as far as I know, those diseases are not super common in Iowa. So why do you think it’s important to have a mosquito surveillance program in a state like Iowa?

Ryan Smith:
Sure. Well, I mean, mosquitoes kind of, as you mentioned, kind of throughout the world, they have a tremendous impact. And while we are very privileged to not have to worry about a lot of these mosquito-borne diseases, even about a hundred years ago still, diseases like malaria were very prevalent here in the United States. And we often kind of forget about that, even in Iowa. And through DDT and other eradication efforts, we were able to eliminate a lot of these diseases. But at least for us in Iowa right now, the most pressing mosquito-borne disease has been West Nile virus. It was originally introduced about 20 years ago, and since then has become endemic. More or less what that means is that every year you are going to have infections. So there may be variation between years, but there will always be cases of West Nile virus.

Ryan Smith:
So it’s something that we can more or less continue to expect in the future, but it’s also something that we’re trying to understand. At least one of the major priorities of our mosquito surveillance program here is to really understand some of the dynamics that are at play and why in one year we can have a hundred cases of West Nile virus and then in the next year we have five, and trying to take that mosquito data and better understand some of these reasons for these fluctuations in disease transmission. And I think not only trying to understand diseases that are here, but I think getting a better grasp of the mosquitoes that maybe aren’t transmitting disease in the case of potential pathogens that are introduced into the area.

Ryan Smith:
So for instance, even a few years ago when Zika virus kind of popped up out of nowhere, there was a big concern of, oh, is there any potential that Zika virus can be transmitted in the United States and, even more relevant to us, in the state of Iowa. Do we have those mosquitoes that can even transmit this disease? So questions like that are, I think, are really integral to a mosquito surveillance program, and I think you can answer the same question similarly for ticks and tick-borne diseases. What ticks do we have? What diseases can we potentially have here in the state?

Radha Velamuri:
You mentioned mosquito data. What is mosquito data, or how do you get this data? What is your day-to-day surveillance of mosquitoes?

Ryan Smith:
Sure. So we have different objectives. Some of it is just general kind of population abundance, seeing what type of mosquitoes we find. But there are also cases in which we’re trying to see if there are invasive mosquitoes coming into the state, and so we use different traps for that. And then with regard to West Nile virus, we also use different traps so that we can collect mosquitoes that we can ultimately test to see if they are infected with that virus.

Ryan Smith:
So ultimately, our surveillance program is made up of at least really three major objectives, and with that, we use different trap types. So ultimately, the types of mosquitoes that we collect are going to be different depending on the exact trap that we’re using. So ultimately, some of these traps are maintained by us here at Iowa State, but a lot of these are maintained through partners located throughout the state. At least right now, I forget the exact numbers, but I think we have partners for six other counties for West Nile virus surveillance. And I think we’re at 10 for some of our invasive mosquito projects.

Ryan Smith:
So ultimately, what that means is, in a lot of these other counties, which are maybe an hour or two away from us here in Ames, is that we rely on local county public health partners or people who are interested in maintaining these traps for us. So they may do the day-to-day operations of changing the traps and doing any mosquito collections that are there. And then ultimately, they send that to us at Iowa State, and we have personnel that will sort through every single insect that is collected, pulling out the mosquitoes and doing identifications of every single one. We speciate every mosquito that we bring in. And from there, we tally all these up, and we’ve had almost about 50 years of data that has been collected here at Iowa State, looking at these different mosquito populations. So with that, we can really get a good sense of where we are now, where we’ve been in the past, and maybe where things are going in the future.

Anya Morozov:
Just curious, do you know about how many mosquitoes get trapped a year that you have to sort through?

Ryan Smith:
Yeah. It really does depend by the year and obviously the number of traps that we have going. The most predominant or most abundant mosquito that we have here, at least in central Iowa, is a mosquito called Aedes vexans. This is a mosquito that doesn’t really transmit any disease, but it is annoying and will bite you. And especially after these large rainfalls, they can come out in really big numbers. Just in a given year, we might process a few hundred thousand samples of mosquitoes as they’re coming in. And we’ve had traps oftentimes where, just even in a single night, we’ve had more than 5,000 of these mosquitoes. There can be so many that they kind of fall out and they’re kind of a mountain of mosquitoes. Sometimes we don’t even sort through all of them. We actually just weigh it to get an approximate number of samples that are there. So they can be in really high numbers sometimes.

Radha Velamuri:
That’s my nightmare. I think you just described my nightmare.

Ryan Smith:
Yeah, no, I can definitely understand that. And trust me, even as someone that works on mosquitoes, I’m still very much prone to getting bitten.

Radha Velamuri:
I’m so sorry. What if you were in an ideal world, and that still has mosquitoes apparently, but you were in an ideal world, how would you like to conduct mosquito surveillance? Is there some trap design you would love to try, or use DNA testing on every single mosquito? What would be your spare-no-expense mosquito surveillance technique?

Ryan Smith:
Yeah. I mean, it’s maybe hard to get a wish list. I mean, maybe more than… I mean, ultimately, our biggest limitation with our surveillance right now is just money and the resources that we can do. Unfortunately, that kind of ebbs and flows with interests of disease. So before Zika came out, the interest in a lot of our mosquito-borne disease and surveillance was kind of waning. Then we had Zika again, so interest kind of popped up, and we had some funding. And then it kind of dropped down.

Ryan Smith:
So ultimately, I guess my wish would be pretty boring and just ask for some consistent funds and be able to run and maintain one of these programs, and to have extra capacity to really ask some additional questions. And maybe if we had some fancy traps, that would save us a lot of time with actually doing the speciation and counting through each and every one of these. There are some of those traps that are being developed right now, but they cost a lot of money, and ones that we can’t really afford to do on our budget. So ultimately, my boring answer is just to have more money.

Radha Velamuri:
I thought you would be like, “I want a machine that can identify every single mosquito that comes in in the blink of an eye,” but you’re thinking practically.

Ryan Smith:
Yeah, I’m too practical from that perspective. I mean, the biggest challenge with having the surveillance program is just having that kind of consistent funding to really grow the program, I guess, as opposed to maintain or put Band-Aids on it to kind of hold it together. So that’s maybe the practicality of it. I’ll kind of save the laser beams and fancy traps out there for someone else to wish for.

Anya Morozov:
You mentioned the different sorts of questions that you want to answer with the mosquito surveillance data. So can you talk a little more about the types of questions you answer and what information you get from conducting mosquito surveillance?

Ryan Smith:
Sure. A long-held question that we’ve had in the lab is obviously thinking about West Nile virus transmission. Who are the mosquitoes that are involved? Why do we have these fluctuations from year to year? And that’s using a lot of our data. So a few years ago, we published a study in which we did a synopsis of the last 15 years of what West Nile virus transmission looked like in the state of Iowa. And from that, we can really kind of piece together and demonstrate that the majority of our West Nile virus cases are out in western Iowa. And the majority kind of imply that these cases are responsible to a single mosquito, Culex tarsalis, which is much more prevalent in that area, and they are able to acquire and transmit this virus much better, kind of really pointing the finger at them as being the most important. Not to say that other mosquitoes that we have in the state can’t transmit it.

Ryan Smith:
But looking at the dynamics of these different mosquito populations is something that has been of great interest to us, and I think that we’ve started to learn a lot about it. But unfortunately, even still, West Nile is relatively new. It’s been here for 20 years, and while that might sound like a lot, when you start to look at epidemiological data, you need to have more time points. So we’re learning more and more with each passing year. And when we first start to feel like we have addressed some questions, we start to kind of shake our head, and with the next season, it’s like, “Well, how come we didn’t more get more cases this year? And how come we didn’t have a bigger impact as far as disease transmission?” And these are things that continue to evolve in the lab.

Ryan Smith:
And some of the other work that we’ve done is more focused on invasive mosquitoes and some of these Aedes mosquitoes that can actually transmit things like Zika virus. We’ve recently detected them here in the state and have argued that they are established in some of the counties, and kind of looking to follow not only where they are, but where they could potentially spread in the future. So we can ask a lot of questions with the data that we have, even pursue other less important vectors of disease and kind of see… Even from the perspective of from a geographical perspective, Iowa’s interesting in its ecology, where there seems to be almost like a gradient of a lot of these different mosquitoes and ticks and where you might find them and where they’re located in the state. We’re kind of at this boundary, I think, for a lot of their range. So I think from that perspective and the ecology of these different vectors that Iowa is an interesting place, and we’re still trying to figure out what exactly are those determinants of the environment that shape where and why we might find certain mosquitoes or ticks in these areas.

Anya Morozov:
So you can kind of watch and see if the ranges change over time too.

Ryan Smith:
And that’s exactly what we’re seeing, is that… With all of this surveillance data, as I mentioned, and that’s the benefit of having decades of this data, is you can see where maybe some of these mosquitoes were 20 years ago and where they are now. And the same goes for ticks. And where you’re seeing this movement or expansion can kind of inform the potential where we might see additional disease transmission in the future. And I think that that’s really important. The problem with the surveillance is that you don’t see the repercussions or the benefits immediately, and like I said, you see this benefit years down the line. So obviously, that’s kind of a hard thing to convince taxpayer dollars, I guess, of the importance. But it is still, I think, really vital and important to really look at these types of questions.

Radha Velamuri:
No, for sure. I totally understand what you’re saying. That’s what it seems like a lot of research is like. You invest a lot of time and effort, but then you don’t… You might not see the results for years to come. Changing gears just a little bit, your lab published an article about finding a new species of mosquito in Iowa. Could you tell us a little bit more about that, because a new species and what it means for the mosquito-borne disease side of things.

Ryan Smith:
Sure. We kind of alluded to it already, but one of these invasive mosquitoes, Aedes albopictus, we recently found here in the state. And Aedes albopictus can be found throughout the world and is spreading in the United States. Previously, it was thought that this mosquito wouldn’t be able to survive here in the state of Iowa just because of the winter. So the winter temperatures were thought to be kind of a limitation as to where you might find it. And even though occasionally you might have some of these mosquitoes be introduced, they just wouldn’t survive.

Ryan Smith:
Well, over the last few years, especially after the importance of this Zika virus epidemic, there was a lot more interest to see whether these mosquitoes were here in the state. And ultimately, we found these mosquitoes in three different Iowa counties, in Lee, in Des Moines County, as well as Polk County, here in Des Moines. And ultimately, what we’ve seen is an increase in these numbers. They seem to really be associated with, I guess, suburban housing, where there’s a lot of vegetation, kind of more populated areas of each of these counties. And so they maybe have some limitations of, I think, the agriculture in these areas as to where they can spread.

Ryan Smith:
But I think it’s an important article from the perspective that we’ve been able to see these year to year. They’re growing. They’re expanding into new areas, really kind of countering that idea that they wouldn’t be able to survive here in the state. So from an immediate perspective, these mosquitoes aren’t going to probably transmit any diseases. They might have the potential in the future, if something that was introduced. But in the meantime, it’s another mosquito that’s going to probably be pretty aggressive in biting us. They really like to bite people and can be a real nuisance from that perspective. So the immediate concerns for disease are pretty rare, if not minimal, but it’s another mosquito species that can definitely be a major nuisance when we’re having those barbecues or outdoor functions.

Anya Morozov:
That kind of is a good segue into prevention. What are some ways to control the spread of mosquito-borne diseases, either at an individual level or a larger scale?

Ryan Smith:
Well, I think at least for most people, it kind of starts at the home. And I think that we can do a lot of measures in and around our homes just to prevent any kind of standing water, removing junk or debris that can collect a little bit of rainfall, any kind of buckets, kids’ toys, little kiddie pools, anything like that that can collect that water. And you would be amazed at… You only need maybe an inch or two of water for these mosquitoes to potentially lay their eggs and to undergo their larval development. So simply removing these water sources or sites in which mosquito development can occur, you’re going to prevent mosquitoes from being close to you. So if you can kind of keep them away from the home, then they would have to travel a lot further to hopefully get you if you happen to be outside. So collectively, if you can do that and your neighbors can do that and even as a community, you can potentially reduce some of the impacts of mosquitoes in and around the home.

Ryan Smith:
And then ultimately, in Iowa, we don’t really have mosquito-control districts or organized mosquito control. There are a few counties, a few cities that do have some spraying efforts, and we do cooperate with them to help their spraying patterns so that they’re not spraying all the time and to really kind of focus on times when there are much higher mosquito numbers. So it kind of takes a tiered response. At least in the state, we don’t have funded resources for this organized mosquito control. We are actually contracted through the state Department of Public Health to do a lot of our surveillance, but as far as any kind of disease-mitigation efforts or anything like that, at least in the state of Iowa, we really don’t have that unfortunately.

Ryan Smith:
So if we were to really have an outbreak or something where we needed additional help, we would probably bring in people from the CDC. So you kind of get this hierarchical effort of people that would respond to a situation. So partners at the CDC, who really kind of monitor and help to reduce any kind of disease in the United States, would probably be employed to help us here in Iowa if indeed anything did pop up.

Radha Velamuri:
We can talk about the United States here, or we can talk about Iowa. We can talk about globally. But what’s your opinion on health equity in relation to mosquito-borne diseases or mosquito surveillance?

Ryan Smith:
Sure. Well, I mean, again, for the United States, there’s really not a huge impact of mosquito-borne disease, as I mentioned before. I think the real inequities are in other parts of the world, and not only for mosquito-borne disease, but a lot of the other vector-borne diseases that are transmitted by like kissing bugs and sand flies. These are predominantly diseases that affect those that are from poor incomes and not having really suitable housing conditions. And oftentimes, many others have mentioned before that if you really want to impact a lot of these diseases and their transmission is we need to build better homes and having places that have four walls and have windows with screens and an actual floor to prevent many of these different arthropods from getting inside and potentially biting us when we are vulnerable and sleeping. I think really those measures are reflected in where we have really the biggest impacts of vector-borne disease. So I think, frankly, building better homes is going to be arguably one of the biggest steps to really reduce bites. And if you can reduce bites, then you can reduce potential disease transmission.

Anya Morozov:
Building better homes. Yeah. So next, we’re just going to ask the question that we ask of all of our guests. What is one thing you thought you knew but were later wrong about?

Ryan Smith:
Yeah, so I think it’s a challenging question. We sometimes think that we’re always right. But I guess one of the more recent examples is… I think it’s important to keep an open mind as scientists, and I think we should always be influenced by new data or new information that can change our minds. And I think the first thing that kind of comes to mind is a recent study that we’ve been doing actually on some of the tick-borne diseases that are found here in the state. And this is regarding a bacterial pathogen that’s transmitted by different ticks. And originally, we kind of had this preconceived notion that this was Rocky Mountain Spotted Fever, Rickettsia rickettsii, that is transmitted by the Dermacentor variabilis, which is the American dog tick.

Ryan Smith:
We don’t have a huge number of cases here in the state, but we were kind of pointing the finger at this tick and this pathogen. And as we started looking more and more into the literature, it was much more vague. So ultimately, our thoughts have changed, and we don’t really think it’s that type of bacteria anymore. We don’t think it’s that tick that’s involved anymore. So it’s really just kind of unwrapping the layers and really kind of following where the data are actually taking us, and I think we can learn a lot more. And our idea of where transmission of this disease is occurring has really changed as a result of taking a different scope or a different lens applied to these questions.

Radha Velamuri:
Yeah. Thanks for the quick preview on tick-borne diseases, which we’ll be talking about in a future podcast episode. That was a really nice segue. Thank you. And we can just wrap up. That was wonderful. Thank you so much for coming onto our show. Yeah, I don’t know what else to say. That was pretty good.

Ryan Smith:
Well, thank you. I appreciate it. I’m always happy to help if you guys have other questions. And if you want to talk a little bit more when it comes to tick-borne disease, we can definitely do that too.

Anya Morozov:
That’s it for our episode this week. Big thanks to Dr. Ryan Smith for joining us today. This episode was hosted and written by Radha Velamuri and myself, and edited and produced by me, Anya Morozov. You can learn more about the College of Public Health on Facebook, and our podcast is available on Spotify, Apple Podcasts, and SoundCloud. If you enjoyed this episode and would like to help support the podcast, please share it with your colleagues, friends, or anyone interested in public health. If you have a suggestion for our team, you can always reach us at cph-gradambassador@uiowa.edu. This episode was brought to you by the University of Iowa College of Public Health. Stay tuned next week for our continuation of the series on vector-borne diseases. And until then, stay healthy, stay curious, and take care.