Itching for Answers

Yosemite National Park receives more than four million visitors per year, attracting people from all over the world to take in the sights and sounds of the park. But sometimes there are unwanted guests that hitch a ride on luggage, clothing, vehicles or have made their way into the park due to climate change and other environmental factors. Lurking amongst the beauty of the rock faces, sprawling meadows, scenic waterfalls and majestic wildlife, are those familiar little pests that take a drink of blood from an unsuspecting human or animal and leave an itchy little bite in its place. You guessed it — mosquitoes. Typically, a mosquito bite is nothing more than an inconvenience – until it isn’t. Mosquitoes can carry vector-borne illnesses that can be deadly or cause permanent health complications, particularly in children.

Yosemite National Park is located in central California in the Sierra Nevada mountains with more than 1,200 square miles (nearly 95% designated wilderness) of public land and a diverse ecology, making it a perfect vector habitat. Park geography and limited resources have historically posed barriers to extensive mosquito surveillance efforts, resulting in a survey not being done in more than two decades.

WCU mosquito expert steps in

For the past 15 years, Brian Byrd, professor of environmental health sciences and supervisor of the Mosquito and Vector-Borne Infectious Disease Facility in the School of Health Sciences at WCU, has been doing extensive research on vector-borne illnesses transmitted by mosquitoes. In 2022, alumnus George Carroll ’09, acting deputy epidemiology branch chief and regional public health consultant for the National Park Service, stopped by to see Byrd on his way back from a training in Asheville and shared the struggles he was having in terms of monitoring mosquitoes. “We got to talking and I shared the problems we were having with mosquitoes and the sheer size of the park, which is roughly the size of Rhode Island,” Carroll said. “He expressed interested in helping, and the rest is history.” Carroll’s sister attended WCU, so it was an easy and familiar choice for him. Initially a marketing major, Carroll stumbled into an into environmental health class where he learned about mosquito-borne diseases and bioterrorism and was immediately convinced that was the major for him. Carroll was one of Byrd’s first students when he came to WCU. Years later, the two have worked together to come up with a plan to conduct a multiyear mosquito survey in Yosemite.

"Hantavirus and ticks have been the main focus of vector-borne illness monitoring,” Carroll said. “Three people died from a hantavirus outbreak in 2012 and ticks have tested positive for Lyme in the park and we also deal with rodents carrying plague. Mosquito monitoring has not been at the forefront of surveillance, coupled with lack of resources and manpower, has made it difficult to know exactly what types of mosquitoes are in the park.” In California, there are more than 50 known species of mosquitoes and at least 15 known mosquito-borne viruses. According to the California Department of Health, the recent human disease burden from endemic arboviruses has been predominantly caused by West Nile virus and St. Louis encephalitis virus. “Over the last 20 years, we have had nine-plus invasive mosquitoes coming to the United States,” Byrd said. “In California, there are Aedes, or more commonly known as container mosquitoes, that lay their eggs in bird baths, gutters, tires and buckets. These species carry diseases like yellow fever and West Nile, and these are invasive up and down the Central Valley and in Los Angeles, so there is always the risk they could show up in Yosemite.”

Byrd and Carroll received scientific research permit approval from the National Park Service for the three-year study in Yosemite. “This is part of a multiyear project that we're doing with the U.S. Public Health Service and National Park Service to document mosquitoes throughout the park, but also to look for invasives, mosquitoes, invasive species, and also to help set up a surveillance program for West Nile virus,” Byrd said. Mosquito populations are not static. They're highly dynamic and sometimes what humans do impact those dynamics. “People are on the move through technology, trade and travel, so people can actually move mosquitoes around,” Byrd said. “In addition, due to our changing weather and patterns with climate change, we're seeing increased range expansion of other mosquitoes. And we've seen that in the Southeast, where mosquitoes have moved up the coast.

There's no reason to believe that the eastern Sierra Nevadas would be immune to that.” The goals of the study are to update parkwide mosquito species records; increase the number and range of collection sites; use survey data to create a mosquito management plan for Yosemite; increase local capacity for future surveillance efforts; reinitiate surveillance in the park and share updated species record with NPS management, staff and visitors. “Last year, we really just focused on sort of reaffirming species records throughout the park,” Byrd said. “This year, our goal is a little bit different, where we're still looking across the park for different mosquitoes, but we're also helping George set up a surveillance program. We're doing that on two fronts. The first one is to look for invasive mosquitoes, particularly ones that love to lay their eggs in containers around the house. Our second goal is really to focus on Culex mosquitoes and mosquitoes that transmit West Nile virus.”

Trapping and tracking

In 2023, Byrd traveled solo to Yosemite to conduct two-week mosquito (adult and larval) surveys in July and October. During this period, he successfully collected from 26 larval and 25 adult sites ranging from approximately 4,000 to 8,500 feet in elevation. Byrd identified 12 mosquito species including: Culex tarsalis (primary West Nile virus vector) and Aedes sierrensis (dog heartworm vector). Byrd also collected several more Aedes species and some Culex and Culiseta species. For the June 2024 trip, Byrd was able to bring along some reinforcements, with WCU students Madeline Craig and Will Parker, and alumni Hannah Alexander ’23 and Mitchell Mullin ’23, to help set traps, and collect eggs, larvae and adult mosquitoes to take back to Cullowhee to raise and identify.

During the first day, Byrd and the students put out 20 small traps to leave out for four days for female mosquitoes to lay their eggs in. “The mosquito will lay her eggs on the piece of seed germination paper in the trap and we take those papers back to our lab in Cullowhee to rear them up to see what types we have,” Byrd said. “The goal of this was to show George how to set the traps and get a jump start on the invasive Aedes surveillance.” Each of the 20 traps were simple black cups with information about the project and GPS coordinates to be able to go back to the area where the trap was set. “With the park being so expansive, we have to prioritize where we go to collect mosquitoes,” Byrd said.

“But mosquitoes haven't really let us down. Pretty much everywhere we've gone across this park, we've been able to find mosquitoes, whether in a hole in a tree or a roadside ditch or the most pristine alpine meadow, we can find those mosquitoes and we look for them in their aquatic stages as larvae.” Holes were drilled in the cups so rainwater, leaves and debris can accumulate and create the perfect setting for egg laying. “When retrieving the traps, you scan it, it asks if there are mosquitoes present and then you export the data,” Byrd said. “I think there's a lot of advantages here, plus you just hit go and you've got some data analysis. Once we got the data from the traps, we left them with George to do another round of trapping in different areas. We set up a mini protocol for future trapping and tracking.”

The traps were set in areas around horse stables, drainage systems, stagnant water in containers as well as highly populated areas within the park. During their weeklong trip, the students also set out gravid traps and ovitraps which target different groupings of mosquitoes. Initiating ovitrap and gravid trap surveillance is one of the main goals for the second year of the survey. “As with any disease, tracking is difficult because people come and go. They can be here one night or a week,” Byrd said. “The odds of them connecting any exposure back to the park or a physician connecting hasn’t happened that I am aware of. So, by doing this surveillance, we know the risk is here and collection can take place and report the findings to the Center for Disease Control or the California Department of Health who can then put out public service announcements about high-risk areas in the park.” An important part of setting the traps is to not disrupt people’s visits to the park or disturb the wildlife.

We don’t want to ruin someone’s hike by seeing a plastic cup out in the middle of the woods, so we have the study number and information about why it is there and try to keep it out of sight as much as possible,” Byrd said. Carroll emphasized the importance of this survey in helping him have a sense of what mosquitoes are in the park and what the disease risks are, something he could not have taken on without Byrd. “We get lots of visitor complaints about mosquitoes so it’s on us to have some sense of what’s here. Getting this baseline of what is here is a huge first step,” Carroll said. “My big goal is to establish routine surveillance and train more park service staff about this and build it into normal park operations.”

Carroll said the shifting climate has made it easier for mosquitoes to quickly invade areas. “We know vector populations, mosquitoes move around, so, if we're not regularly monitoring that poses risk to us, we're not going to know what's here,” Carroll said. “I think across the spectrum of environmental health nationally, there's not a lot of attention paid to vectors. Typically, we're focused on food safety and drinking water. And this is kind of down the list typically, but I know just with the shifting climate vectors move around, mosquitoes move around in different areas they haven't been before, and making it easy for invasive species to come in.” In addition to trapping the survey includes processing the mosquitoes. “When we process, we use microscopes to sort mosquitoes and then pin them,” Byrd said. “Some of the students work with the larvae, but ultimately, the samples have to end up back in our lab in WNC, so we try to identify most of them using what we call morphological techniques. We use a microscope and sort of keys to identify them. On occasion, we have to work with our colleagues across the university, particularly in forensic science, to DNA barcode them to identify exactly what species it is.”

Student experience

Carroll was grateful to Byrd and the students for helping him undertake such an expansive project. “This was basically a homework project I had for a few years,” Carroll said. “I was never able to complete it on my own, so to be able to pull in Dr. Byrd was a rare circumstance, but that just shows the impact he has. I was thrilled to meet the students and have them here to help us carry out this work. When I was in undergrad, I did some mosquito projects but this has been such a great field experience for them.” Parker, a junior from Decatur, Alabama, was excited to return to Yosemite and work on such an important project. “About four years ago, I went to Yosemite for just a few hours, so I really didn’t get to experience much of it,” he said. “Getting to spend a week here doing research is amazing. I recently just switched over to environmental science so getting to do things like this eases my uncertainty about what I want to do.

I now see that being outdoors and doing research might just be my calling.” Parker, a Type 1 diabetic since childhood, loves to challenge himself to do things like hiking and being in the woods, not allowing his illness to hold him back. “Being out here, challenging myself and doing this great work is exciting and I am even more excited to see the results of what we find,” Parker said. “It's an important study because mosquitoes are very deadly vectors on this planet and I think people don't realize that. But being in the lab, I've kind of gotten to understand just how fulfilling this work is, but also how dangerous mosquitoes can be. And even in Western North Carolina, they're a pretty big threat there, too.” Mullin, a biology graduate student from Lawrenceville, Georgia, received a bachelor’s in environmental science and environmental health in 2023.

“I felt like something was missing in my life and it was probably the mountains of WNC,” Mullin said. “I also wanted to learn more and Dr. Byrd approached me when I was working with him during the summer of 2023 and offered me a USDA grant position for me to do some research with him. So, I thought about it and decided to come back to WCU to get my master’s. Biology is different from environmental health; it is more focused on the hard sciences, so it is a change for me but I really enjoy it.” During his undergraduate years, Mullin worked with Byrd in the vector lab on campus. “Dr. Bird was my adviser for three years. I took a couple of courses with him, including the medical entomology course, where we study mosquitoes specifically and I just really liked it,” Mullin said. “I approached him near the end of the semester about helping out in the lab. He gave me a small position so I did that for a summer semester and now I'm here for my master's.” Mullin is currently working on a paper about the impact of an invasive mosquito species called Aedes Japonicus in the Great Smoky Mountains National Park, which sees around 13 million visitors per year. “Doing the research here at Yosemite and writing this paper, if you really stop and think about it, there's all these diseases that could potentially be around the different national parks, some of them maybe not as properly surveyed as others, making them a little harder to find,” Mullin said.

“It is very important to look for these mosquitoes that can vector these pathogens, that can cause diseases in humans and even dogs. It's important to be able to track that, to let people know the risk coming in here and how to protect themselves, their families and pets.” Alexander, a biology graduate student from Charlotte, earned her bachelor’s degree in biology from in 2023 and has been working in the lab with Byrd for the past year. “I'm excited to be out here with some of our lab mates that I did not know super well before we came out here. Getting a weeklong trip is a great teambuilding exercise,” Alexander said. “Also getting to meet some of the professionals that Dr. Byrd works with out in the field like George, is amazing. I am so excited to be able to come out here and help with the survey and see the different career paths that are out there.

A lot of the time when you are doing lab work, you pigeonhole yourself, like I have with salivary glands in mosquitoes, so it is nice to be outdoors doing research.” Craig, a senior from Sylva studying biology, was thrilled to have this opportunity. “As a nontraditional student returning to school after several years away, it is nice to work with Dr. Byrd and get this type of experience,” Craig said. “I have been working in the lab with him for about a year now and he makes it a priority to give students these opportunities to get real field work done.” The students knew Byrd was working on this project for Yosemite, but they did not dream they would be able to help with the research onsite. But the students have echoed, Byrd will find a way to make something happen if it will benefit students. “With Dr. Byrd, if you want something to happen or need something, he is going to help you and make it happen,” Craig said. “This trip shows that and another example is last year he was teaching a course that I couldn’t get in, but he let me attend some of the lectures and field trips just for the experience. He is just such an integral part of my positive experience at WCU.” Alexander was thrilled to be able to collect samples from snowmelt puddles, which is not something she has been able to do back home in Cullowhee. “We’ve never seen any snowmelt Aedes mosquitos before, so that has been really cool to see. We even collected some adults. I am looking forward to looking at those through the scope,” she said. “This work that we're doing is super important because the climate's changing. It's getting warmer; mosquitoes can fly and so they're on the move. They are dangerous.

They carry a lot of different pathogens, from viruses to parasites.” Byrd is happy to see the positive impact these types of trips have on students. “These kinds of immersive trips can be very impactful for students. To begin with, they get to see the work they've been doing in the lab has meaning,” he said. “They are getting to work with park staff out in the field, collecting mosquitoes, identifying them and the final report will also be meaningful. It will be something the park will use. The students are out here making decisions on the fly and they have to be resilient and think on their feet. It is also a great opportunity for them to build camaraderie with one another.” Byrd has spent a lot of time in national parks but being able to share this with students who are getting to experience the sights for the first time is very special. “Being able to share this with them, it really pulls on the heartstrings to see their faces light up and just see places and find new mosquitoes, things they've never seen before,” he said.

“When I bring students on field trips, in the back of my mind I often have a checklist of things I want them to see or think about, that they can build on from other things we've done in the classroom or in the lab. One of the beauties of doing authentic field research is you can't predict what's going to happen so that sort of newness or what we often call trail magic, shows up while we're out here in the field. That's often a nice surprise for me.” Byrd said he gets a lot of satisfaction from teaching and being in the lab, but field work is an entirely different experience. “There's nothing like the field experience, being in an amazing place like WNC is home for us, so we get to experience that beauty every day” he said. “But to come to a place in the eastern Sierra Nevada mountains and see something completely different, everything these students are seeing is new, it is an amazing experience to be out in the field doing work.”

Even though WCU is a regional comprehensive institution located in the rural mountains of WNC, in the field of research, the university is moving those mountains. “Although probably a lot of people think of WCU as a small university, I always like to say we ‘always hit above our weight class’, and in one way we do that is in mosquito-borne diseases,” Byrd said. “It's not a common piece of knowledge, but WNC is a hotspot for a mosquito-borne disease called Lacrosse encephalitis. That's our sort of bread and butter, our main focus in our lab. Our students are working on meaningful, real-world projects around that disease, often catching the attention of the broader research community. And that's been reaffirmed through research contracts, research grants and our students going on to graduate programs and professional programs across the nation.” Seeing Carroll take the initiative to start this surveillance makes Byrd proud.

“George was one of my first students when I came to Western Carolina about 16 years ago and it's been a pleasure to watch him grow professionally,” Byrd said. “He is essentially the public health officer for this entire national park and 3 or 4 other parks. Getting to work with him has been a lot of fun and great to work with somebody who is literally boots on the ground. You'll see him in his uniform, he has boots and he's the backbone of public health here. To be able to help him out and for me and our students to learn from it at the same time is just extraordinary.” Carroll said WCU is what made him into the professional he is today. “Western Carolina made my career, being an environmental health major lead to my first job,” he said. “It was the reason I was successful in that first job. It's the reason I got this job I have now and everything goes back to that undergraduate education. I still use everything to this day.”