It seems like summer overstayed its welcome this year, as many aesthetic walks in Freedom Park have been thwarted by the oppressive heat or downpours. So far, the lattés are staying iced, the boots are lingering below the calf and the felt hats are returning to the coat rack.
But one organism is loving the prolonged summer weather: mosquitos. The southeastern United States has the highest number of so-called “mosquito days” in the country. Western Carolina University’s Mosquito and Vector-Borne Infectious Disease Laboratory received nearly $1 million dollars from nonprofit NCInnovation to probe mosquitos for infectious diseases.
“We probe them with infrared light,” said Scott Huffman, a professor of chemistry at Western Carolina University. “The light that we gather from that — the reflective light — provides information about the chemistry of the mosquitoes.”
Huffman flashes the mosquitos with infrared light. His spectroscope records the light that reflects off the mosquito, returning a squiggly graph. The squiggles can tell Huffman a lot about the mosquito, such as its age, sex and whether it’s carrying any pathogens.
He’s specifically looking for mosquitoes carrying La Cross encephalitis, a virus that can cause brain inflammation. The U.S. Centers for Disease Control have recorded more cases of La Cross in North Carolina than any other state, though those reports represent only a small number of total infections, according to Brian Byrd, director of the lab.
“Those 17 cases a year represent maybe 100 to 300 infections that occurred that either had no symptoms, or you had mild infections where there was no healthcare seeking,” Byrd said.
Not everyone is so lucky. Severe cases of La Cross Encephalitis can cause seizures, paralysis and other neurological problems. Because it’s a virus, like West Nile or Dengue, antibiotics won’t cure the disease. Instead, healthcare providers can only support patients while they recover on their own.
The equipment that Huffman uses is as precise as it is expensive, making it less accessible to organizations like local health departments. By developing a program using machine learning and testing said program on less fancy equipment, Huffman and Byrd can develop a system that labs across the state can afford.
“In North Carolina, there's over 65 species of mosquitoes. Some are problems, some are not,” Byrd said. “And for La Cross, there's one main mosquito that transmits this disease.”
Two invasive species of mosquito also carry it. The Asian Tiger Mosquito can transmit La Cross as well as the West Nile virus. The West Nile virus spread from the East Coast to the West in the early 2000s and remained a steady presence in the states since. North Carolina reported 15 West Nile cases last year.
While your individual risk of contracting these diseases remains low, human development has created conditions for transmission numbers to increase. Warm, humid days are on the rise across the country, which means more time when pest bugs are active.
Mosquitos aren’t the only species experiencing an uptick. Instances of Lyme disease, a tick-borne illness, have spread across the United States. Twenty years ago, Lyme was largely limited to northern states. Cases in North Carolina have risen steadily; in 2008, there were 47. Since 2015, more than 200 cases have been reported each year.
As the combustion of fossil fuels, such as oil and natural gas, continues warming our planet’s atmosphere, mosquitoes are adapting well to the changing climate. A warmer atmosphere holds more moisture, which means heavier rains in some regions; mosquitos breed and mature in the stagnant pools left behind by stormwater.
After a flash flooding event like Hurricane Helene, mosquito populations will likely soar. But that doesn’t mean infections will increase right away.
“They’re going to keep you from hanging out in your backyard, but it may not necessarily be a disease risk,” Byrd said.
When mosquitoes drink the blood of animals infected with viruses, like West Nile or La Cross Encephalitis, they become vectors for the disease. It has no effect on the mosquito; the virus hitches a free ride until the next time its host feeds. If the virus has reached the bug’s salivary gland, the mosquito’s backwash can infect a person. For this reason, young bugs present less risk to humans, and knowing how old mosquito populations are can help public health officials assess that risk.
“The risk may be when the mosquito numbers are low because those few mosquitoes have come in more contact with infected ‘reservoirs,’” Byrd said.
It doesn’t take many mosquitos to cause a problem. In regions where temperatures have risen and relative humidity has dropped, drought conditions set in quickly. This rapid drying brings birds and bugs together around the remaining pools of water.
“Because there's limited water habitat, you actually can end up with lower mosquito numbers but higher risk,” Byrd said.
Warmer weather isn’t the only gift humans have given to our pests; mosquitos love a messy yard. When homeowners leave pots, containers, and other surfaces where standing water can collect, they create a mosquito breeding ground around their homes.
The distance a mosquito travels depends on its location. Along the coast, researchers documented coast-dwelling mosquitos traveling tens of miles from where they spawned. In a more densely populated area — say Mecklenburg County, for example — mosquitos stick to a few hundred-yard radius. Still, mosquito control is a community effort; just because your backyard is dry, doesn’t mean your neighbor has taken similar precautions.
“They're in these containers, gutters, tires, buckets, bird baths,” Byrd said. “If we’re looking for that problem, it should be somewhere close. But it could certainly be a neighbor.”
