Mosquitoes spread rare disease through East Tennessee, and they’re more active

By Ben Cathey (WVLT8) and Priyanka Runwal (Climate Central)

This story was produced through a collaboration between Climate Central and WVLT 8 in Knoxville.

It started with severe headaches and fatigue but within a few days, Huck Zimmerman was struggling to speak clearly. He started to forget what he was saying mid-sentence and seemed loopy.

“He just started really really tanking,” said Sarah Zimmerman, the teenager’s mother. “He kind of went into a hallucination state.”

At the East Tennessee Children’s Hospital in September of 2019, doctors suspected and later confirmed Huck had La Crosse encephalitis—a relatively uncommon viral illness caused by the bite of infected mosquitoes. The virus predominantly affects children.

Rebecca Trout Fryxell of the University of Tennessee. Credit: Scott Wilk/WVLT

Every year, the U.S. reports about 50 to 150 La Crosse encephalitis cases, about 10% of which were recorded in western North Carolina and East Tennessee alone, a hotspot for the disease where few are aware of its existence.

“I was clueless,” said Sarah, who previously worked as a community health educator for the Knox County Health Department. “I had no clue about La Crosse.”

The disease has no cure and most infections remain undiagnosed or undetected until severe symptoms occur and the patient is hospitalized. 

“This [La Crosse] is a virus and vector-borne disease problem that has been neglected and needs attention,” said Rebecca Trout Fryxell, a medical and veterinary entomologist at the University of Tennessee.

Even as awareness about the disease among the larger public is limited, threats of being bitten by an infected mosquito are increasing as carbon pollution traps heat, warming temperatures.

“The amount of time we’re exposed to mosquitoes is now lengthening,” Fryxell said.

Science and news group Climate Central analyzed weather data from Knoxville going back to 1979, and found that the mosquito season has increased by 23 days since then. The specific combination of temperature and humidity that puts humans at risk of mosquito bites now occur more than six months of the year, on average.

What is La Crosse?

Eastern treehole mosquitoes that breed in standing water in tree cavities, discarded tires or unwashed bird baths, primarily spread the La Crosse virus. These mosquitoes feed on infected mammals like chipmunks and squirrels and transmit the virus to humans.

Other stagnant water-breeding species including the invasive Asian tiger mosquito can also spread La Crosse as well as other mosquito-borne diseases like West Nile and eastern equine encephalitis in East Tennessee.

Most people who get exposed to the La Crosse virus may not show symptoms, but some—especially children under 16—could develop a severe illness due to inflammation of the brain.

Symptoms appear within five to 15 days of the infected mosquito bite.

“It can come on fairly suddenly with headache, fever, vomiting, just not acting right, lower energy levels,” said Joe Childs, Chief Medical Officer at the East Tennessee Children’s Hospital.

In acute cases, patients can develop seizures, coma, and paralysis. In the long-term, the infection can impair neurological and cognitive functioning contributing to memory and speech issues, brain fog, and the ability to stay sharp and focus.

Even after two weeks in intensive care, followed by weeks of physical and speech therapy and months of cognitive therapy, 16-year-old Huck still struggles with memorization, slow cognitive processing speed, and multitasking.

“He’s at capacity trying to make it through school even with accommodations,” his mother said. She worries about him being unable to hold a part-time job or drive.

The disease has no specific treatment, and doctors typically work toward managing symptoms.

“Most do have a really good recovery,” Childs said. But in some cases where the brain experiences more swelling, it can take months or longer to be symptom-free, he said.

Mosquito monitoring and management

Starting in the spring, Knox County public health officials set up traps to monitor mosquitoes for presence of harmful viruses. They also test mosquitoes in areas where the health department records positive human cases. To stop the insects from multiplying, they spray breeding grounds with larvicides.

But resources for mosquito surveillance, management, and community education particularly for the La Crosse virus, are still limited.

To fill the gap, Fryxell developed a program to train middle and high school students and educators in East Tennessee in mosquito collection and basic identification and to teach them about the La Crosse disease.

Prevention is key, especially with a lengthening mosquito season. This includes draining standing water, using insect repellants, and wearing long-sleeved shirts and long pants when outdoors in mosquito-friendly areas.

“Where prevention is possible that’s definitely very important,” Childs said. “You certainly don’t want to have this.”