CHILLICOTHE, Ohio — Health officials in Ross County have confirmed the first human case of La Crosse virus in 2025, marking an early detection of the mosquito-borne illness. The Ross County Health District (RCHD) reported the case on Wednesday, urging residents to take precautions to prevent further infections.
La Crosse virus, transmitted through the bite of infected Eastern Treehole mosquitoes (Aedes triseriatus), typically causes mild or no symptoms in most people. However, severe cases can occur, particularly in children under 16, who are most susceptible to serious illness, according to Morgan Kelley, RCHD’s Public Health Nursing Director. Symptoms of severe cases may include fever, headache, nausea, vomiting, and, in rare instances, neurological complications such as encephalitis. The virus is not contagious and cannot be spread from person to person.
“La Crosse virus is spread to humans by the bite of an infected mosquito,” Kelley said. “While most people infected do not show symptoms, we encourage residents to take preventive measures to protect themselves and their families.”
The Eastern Treehole mosquito, the primary carrier of the virus, breeds in small pools of standing water, such as those found in tree holes, discarded tires, and other artificial containers. To combat mosquito breeding, RCHD is hosting its annual tire drive on Saturday, October 11, at the Ross County Fairgrounds. The event, free for county residents, allows individuals to drop off up to 10 rimless car tires per vehicle to reduce potential breeding sites.
“Scrap tires are a common breeding ground for mosquitoes, including the Eastern Treehole mosquito,” said Kelly Spindler, RCHD’s Director of Environmental Health. “Limiting mosquito breeding sites is crucial to preventing mosquito-borne illnesses.”
Spindler also emphasized the “Dress, Dump, and Defend” model to reduce mosquito bites and populations. Residents are advised to wear long sleeves and pants, use EPA-approved insect repellents containing ingredients like DEET, Picaridin, or oil of lemon eucalyptus, and regularly empty standing water from containers around their homes.
The tire drive, funded by the Ross County Litter Control & Solid Waste District’s Community Cleanup Grant, will run from 8 a.m. to noon and include a flu shot clinic. Residents seeking flu shots are asked to bring identification and insurance cards. For tire drive details, contact RCHD’s Environmental Health office at 740-775-1158; for flu shot inquiries, call Public Health Nursing at 740-775-1146.
Background on La Crosse Virus
La Crosse virus is a mosquito-borne illness first identified in La Crosse, Wisconsin, in the 1960s. It belongs to the family of arboviruses and is primarily transmitted by the Eastern Treehole mosquito (Aedes triseriatus), which thrives in wooded areas and urban environments with standing water. The virus is most prevalent in the Midwest and Appalachian regions of the United States, with cases typically reported in late summer and early fall.
While most infections are asymptomatic, severe cases can lead to La Crosse encephalitis, a rare but serious condition that causes inflammation of the brain. Symptoms of severe infection include fever, headache, vomiting, seizures, and, in extreme cases, coma or permanent neurological damage. Children under 16 are at higher risk for severe disease, though fatalities are rare.
There is no specific treatment or vaccine for La Crosse virus. Management of severe cases focuses on supportive care, such as hospitalization for neurological symptoms. Prevention is key, with public health efforts centered on reducing mosquito populations and encouraging personal protective measures. Regular removal of standing water and community initiatives like tire drives are critical to controlling the spread of the virus.
Health officials continue to monitor for additional cases in Ross County and urge residents to stay vigilant as mosquito season continues.