KNOX COUNTY, Tenn. (WATE/WJW) – Two children in Tennessee are now recovering at home after being hospitalized for La Crosse virus, a rare mosquito-borne virus that can, in severe cases, lead to inflammation of the brain.

The Knox County Health Department said the two children were hospitalized earlier this month. They mark the first cases of the virus this year in the county, according to health officials.

Meanwhile in Ohio, a 66-year-old man was recently confirmed to have contracted La Crosse virus, Nexstar’s WJW reports.

What is La Crosse virus?

La Crosse virus is a mosquito-borne infection. Most people who get it don’t have symptoms, but those who do can have a fever, a headache, nausea, and vomiting, Knox County health officials said. In rare cases, it can become severe and lead to inflammation of the brain, or encephalitis.

“Severe disease occurs most often in children under 16 years old,” said a KCHD spokesperson. “Most severe cases require hospitalization but will recover with supportive care. However, up to 15 percent of cases can have major neurologic complications.”

According to the Centers for Disease Control and Prevention, between 30 and 90 La Crosse cases are reported annually. But this number is thought to be a “substantial under-diagnosis” due to the “under-reporting of less severe cases.” Cases are primarily found during the late spring through early fall while mosquitoes are most active.

How is La Crosse virus spread?

It comes from the bite of an infected Aedes triseriatus, or eastern treehole mosquito.

The Aedes mosquitoes primarily bite people in wooded areas during dawn and dusk.

“They are a little bit more of a shy mosquito, they don’t aggressively come out and bite people,” Caroline Terakedis, director of environmental health services for the Tuscarawas County Health Department, told WJW. “It’s difficult to treat standing water for them because they prefer to breed in small tiny areas like tree holes, but they really like scrap tires.”

Humans do not spread the virus, the CDC says. Symptoms can occur within five to 15 days of a bite.

Where have cases been reported?

CDC data shows that between 2003 and 2024, more than 1,500 cases of La Crosse virus were reported, with 15 confirmed deaths over the same time period.

Nearly two dozen states saw at least one case of La Crosse virus during that time. North Carolina and Ohio each saw over 300 cases, while Tennessee and West Virginia had over 200 each. Other states that recorded at least one case include Alabama, Florida, Georgia, Iowa, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Missouri, Mississippi, Rhode Island, South Carolina, Texas, Virginia, and Wisconsin.

The vast majority of human cases reported to the CDC were among those under the age of 18.

How to avoid getting La Crosse virus

Similar to advice for preventing West Nile virus, health experts recommend using insect repellants (such as DEET, Picaridin, IR3535 and oil of lemon eucalyptus), treating your clothes with repellents like permethrin, wearing long-sleeved shirts and pants while near wooded areas, and covering strollers with mosquito netting.

Knox County health officials also recommended reducing standing water on your property to control the mosquito population. This includes turning over items that hold water, like flowerpot saucers, once a week.

Health officials have advised parents and guardians to seek emergency care if they see neurological issues in their children. This would include seizures, mental changes, and drowsiness or trouble staying awake.

The Tuscarawas County Health Department says there is no vaccine against the virus, and there are no medications to specifically treat La Crosse encephalitis.

WATE’s Hannah Moore and Nexstar’s Addy Bink contributed to this report.