Arizona researchers turn to mosquito DNA in their hunt for the sources of West Nile virus
Researchers at Northern Arizona University can only open the sub-zero freezers inside the Pathogen and Microbiome Institute lab for a few moments, or else they risk spoiling the precious specimens inside: frosted tubes crammed with mosquitoes from Maricopa County.
Though Flagstaff is turning colder as winter approaches, a few hours south of the lab, Maricopa County was hot and sunny well into October — perfect conditions for mosquitoes. Collecting and studying these mosquitoes is key to stopping the West Nile virus that spreads from this county every year.
Leading the research, NAU evolutionary biologist Crystal Hepp wants to answer one question: Where is the West Nile virus found in Arizona and neighboring states coming from?
To do this, her team pulverizes hundreds of frozen mosquitoes into a clear liquid soup from which they can extract DNA. Then, almost like a detective in a mystery, Hepp strings together the DNA information to trace the virus back to its source.
This is vital information for the state's fight against West Nile virus, which infected over 170 residents in 2019 and was responsible for the deaths of 17 people. Most of those cases came from Maricopa County, which genetic researchers at NAU and at Phoenix's Translational Genomics Research Institute determined is an ongoing source of West Nile infections for the Southwest.
The same researchers also determined that West Nile virus has become a permanent part of Arizona's ecosystem.
Pinpointing mosquito hot spots
When mapping the West Nile virus DNA from the mosquitoes, Hepp discovered that many strains of the virus in the Southwest appear to originate in the southeast part of Maricopa County.
Using genetic analysis, Hepp is zeroing in on West Nile hot spots that can potentially be fogged with pesticides.
"Southeast valley is huge," she said. "They're not going to go in and fog the entire southeast valley. We need to have these very pinpointed locations."
Hepp's DNA analysis leads back to a few key areas within Maricopa County. One big breeding ground for the virus is near the intersection of Loop 101 and Loop 202, according to Hepp.
"If you drive by there, you'll notice that the Salt River backs up and there tends to be a lot of water that pools in that particular area," she said.
A second hot spot Hepp found was in the town of Gilbert, which she said may have to do with landscaping for soft, grassy lawns or pools.
In one Gilbert neighborhood, when Maricopa County Vector Control Supervisor Jim Will steps out of his truck, he can hardly walk a few feet before being sprayed with an automatic lawn sprinkler.
Pointing out puddles of water pooling in low-lying areas, he explained, "If that doesn't drain within 72 hours, it can give a breeding site for mosquitoes."
As he approaches a mosquito trap that Maricopa County Vector Control placed in the neighborhood, the steady hum of mosquitoes' buzzing grows louder alongside a whirring fan that sucks mosquitoes into a long net.
Every week, Maricopa County places 811 of these traps throughout the county, but this one — saddled between a bike path and a playground — consistently ensnares dozens of mosquitoes.
'It's just miserable' for the kids
A few doors down, Gilbert resident Jax Kyle is all too aware of the neighborhood's mosquito problem. Her legs are covered with spots. Some are pink, angry bumps — signs of a fresh mosquito bite — while others are crimson scabs that formed after frenzied scratching.
"I've literally been covered in mosquito bites," she said. "I had about 60 mosquito bites that I counted on my leg at one time."
DEADLY VIRUS:Arizona is leading the nation in West Nile deaths
While the bites can be itchy and annoying, Kyle is more scared of the diseases they might be bringing. She has multiple sclerosis, which means that her immune system is compromised and may not be as effective at fighting diseases like West Nile virus.
"If people who are seemingly healthy can get sick or even die from it, it's really worrisome to someone like me," she said.
Kyle said she is also worried about kids being bit. Her development teems with children who run around throughout several neighborhood playgrounds.
Nearby neighbor Anna Foss, a mother of four, said she tries to limit the amount of time her children play outside, especially at night. When they do go out, she covers them in mosquito repellent and encourages them to wear long sleeves. But that doesn't stop them from being bit.
"They get eaten alive," Foss said. "It's just miserable for them."
Foss has another theory to explain why her neighborhood is infested with mosquitoes: clogged storm drains. She said financial records provided by Heywood Community Management, the neighborhood's homeowners association company, show that there has been no maintenance on the storm drains since April 2017.
"We've been asking questions and not gotten any responses from the management company regarding the storm drains," Foss said.
Heywood Community Management, which services over 80 communities throughout the county, has not responded to multiple email and phone requests for comment.
'Wigglers' take refuge in smelly drains
When looking closely at one storm drain near Foss' house, the pungent smell of a humid cesspool assaults the senses. The water in the drains is black, littered with leaves and completely still, save for a few insects skimming the surface.
"It just collects this mud pile," Kyle said. "There could be anything in there, there could be ebola virus for all we know, because it's just so disgusting."
After scooping water from one of these drains, Will can easily identify the mosquito larvae: tiny crescent-shaped specks.
"We call them wigglers," he says as the worm-like larvae swim toward the surface of the water for air.
Backed-up storm drains are perfect breeding grounds for the type of mosquito that spreads West Nile virus, according to Will, and it's a problem he said he sees often.
"Some of it's design flaws," he said. "The second part is ... the drains at the bottom of them haven't been cleaned in a long time, so the water doesn't drain properly."
This neighborhood is one of several that has been fogged with pesticides 8 to 11 times by Maricopa County Vector Control in 2019. By working with genetic researchers like Hepp and mapping the virus, Maricopa County hopes to target the virus to prevent big outbreaks in the future.
Mosquitoes could develop resistance
However, some mosquitoes have mutations that make them immune to certain pesticides, and they don't die when fogged with those pesticides. Instead, they reproduce and over time, the mosquito population can become more and more resistant to the pesticides the county uses to kill them.
"So what we want to know is how resistant are our mosquitoes to pesticides and also what pesticides are they resistant to," Hepp said.
So far in her analysis of Maricopa County mosquitoes' DNA, Hepp said she has seen signs of pesticide resistance.
Hepp's research has given the county a better understanding of West Nile virus and other mosquito-borne diseases, but it's been a slow-moving process.
Hepp started working on this research project in 2017 and said she has ramped up the amount of DNA that she is analyzing over the past year. She said she still has to analyze DNA from hundreds more mosquitoes across the county before she can make any official conclusions or recommendations.
In the future, Hepp said she will work on a collaboration with the Sonora, Mexico, region to try to implement a mosquito surveillance and tracking program there too, since mosquito-borne diseases can travel between the border of Arizona and Mexico.
"We are trying to develop proactive interventions rather than reactive interventions," Hepp said.
Her hope is that advanced genetic research might one day allow Maricopa County to stay one step ahead of nature, stopping West Nile virus in its tracks.
Amanda Morris covers all things bioscience, which includes health care, technology, new research and the environment. Send her tips, story ideas, or dog memes at firstname.lastname@example.org and follow her on Twitter @amandamomorris for the latest bioscience updates.
Independent coverage of bioscience in Arizona is supported by a grant from the Flinn Foundation.
Support local journalism. Subscribe to azcentral.com today.