On any given day between May and November, Bethany Bolling and her team of microbiologists at the Texas Department of State Health Services laboratory in Austin can be found sorting and sucking up mosquitoes for testing.
“The Culex species, we test for West Nile virus, Saint Louis encephalitis virus and Western equine encephalitis virus. And then our Aedes species mosquitoes, we test for Zika virus, chikungunya virus and the dengue viruses. Once we do the testing, if we detect any positive or virus-positive mosquito pools, then we call the local jurisdiction that sent us those mosquitoes and let them know there is virus activity in their area,” Bolling says.
The state lab tests thousands of samples each year. The process takes several days, as staff sort the mosquitoes by gender and species. Only female mosquitos drink blood, so only they can spread disease. Those that will be tested are essentially ground up and run through sophisticated devices that detect molecules of viruses. If a mosquito pool is positive, local health departments are notified. Bolling says they can then take actions to treat infected areas and warn the public.
“We provide this service, this testing service, free of charge to our submitters. All they have to do is have the resources to set out traps and ship us the mosquitoes,” Bolling says.
Less than 20 percent of Texas counties and just a handful of cities submit mosquito samples. Though the testing is free, many jurisdictions just don’t have the budgets to allow for the trained staff and equipment needed for the job of mosquito surveillance. For some, it may not be cost-effective, given that usually only a handful of samples test positive. In 2017, the state lab tested more than 22,000 pools of mosquitoes. Less than one percent, or 132 of those pools, tested positive for West Nile.
But what if there were a way to pinpoint and target the most likely areas for the disease? That’s the idea behind a project underway in Harris County. It’s a collaboration between Harris County, the Baylor College of Medicine in Houston and ExxonMobile’s philanthropic arm known as the ExxonMobile Foundation. Melissa Nolan helped spark the idea. She’s now with the University of South Carolina but was a researcher at Baylor when she struck up a conversation with the medical director for Exxon Mobile at an awards dinner in 2017.
“So we were sitting around talking about why it’s so hard to control for malaria and some of the different components of that, and the concept of being able to prioritize and identify the most impactful areas that mosquitoes could be breeding came up,” Nolan says.
The conversation turned to a technology Exxon uses to evaluate the environmental impact of its activities and find new drill sites, called remote sensing.
It turns out that remote sensing utilizes satellite imagery that is of such high resolution, it can tell users about small items on the ground like tires and birdbaths, as well as larger land features like ditches that may be inviting to mosquitoes for breeding.
Sarah Gunter is a vector-born disease expert and current member of the team at the Baylor College of Medicine working with the technology. Using high-resolution images of the area and information about the habits of different types of mosquitoes, she and several team members developed a preliminary predictive model of hotspots in the county where Culex and Aedes mosquitoes might likely be found.
“It’s some really powerful imagery,” Gunter says. “It’s actually a multiband imagery, so we have not only visible light spectrum but also infrared. So, it allows us to gather information about vegetation and water on the surface of the earth, which is important for us when we consider mosquito-breeding habitat because mosquitoes breed in water, and a lot of the water has to have vegetation close by or in the water itself.”
This is where the Harris County Mosquito and Vector Control Division comes in. This past summer, crews placed three different types of mosquito traps in locations chosen by the research team; they needed samples to determine whether the model’s predictions were accurate. Dr. Mustapha Debboun is the director of the division.
“We collected and sampled throughout the summer, from June until the end of September. That was our function: to do the trapping, the collection of the mosquitoes and, of course, to identify the mosquitoes when you bring them to the lab,” Debboun says.
Harris County has its own lab, and tests for West Nile and other viruses on-site. Debboun says the data is still being analyzed and there will be at least one more round of testing, or validation, next summer. But he has high hopes for the kind of impact this method could have in the future.
“We’re creating an innovative, evidence-based method to target abatement efforts that has promise to ultimately reduce the burden of mosquito-borne diseases locally, nationally and globally,” Debboun says.
And the method is relatively low-cost and highly transferable – meaning it could be used to target habitats of other disease-carrying insects.
Gunter at the Baylor College of Medicine says: “Another one of our long-term goals is to expand this beyond just these species of mosquitoes that are transmitting diseases of human importance in Texas and the southern U.S., to look at maybe other species that are important vectors throughout the world as well as other vectors of disease – things like ticks or kissing bugs and sand flies.”
The technology may give us reason to be optimistic that many vector-borne diseases could be better managed in the years to come. But for now, put on that insect repellent, wear clothes that cover your arms and legs and stay away from places where mosquitoes or other disease-infested insects may be lurking.