ROSS COUNTY, Ohio — The Ross County Health District is urging residents to take precautions against mosquito bites after a mosquito pool collected in Colerain Township tested positive for La Crosse virus.
Health officials emphasized that no human cases have been reported in Ross County in 2026, but the positive mosquito sample serves as a reminder that the virus is present in the area.
La Crosse virus is primarily spread by the Eastern Treehole mosquito (Aedes triseriatus), an aggressive daytime-biting mosquito commonly found in wooded areas. While many people associate mosquitoes with dusk and nighttime activity, health officials warn that this species is active during the day, making daytime protection equally important.
According to the Ohio Department of Health, Ohio reports more human cases of La Crosse virus than any other state, averaging about 20 cases each year. Although most people infected with the virus never develop symptoms, some can experience illness beginning with fever, headache, nausea, vomiting, and fatigue.
In more serious cases, the virus can cause encephalitis, or inflammation of the brain. Severe illness occurs most often in children younger than 16 years old.
To reduce the risk of mosquito bites and help control mosquito populations, the Ross County Health District recommends residents:
- Eliminate standing water around homes by emptying containers at least once a week.
- Wear long sleeves and long pants whenever practical.
- Apply EPA-registered insect repellents containing DEET, picaridin, oil of lemon eucalyptus (or PMD), or IR3535 when spending time outdoors.
The health district is also offering free mosquito larvicide tablets on a first-come, first-served basis for residents to treat standing water that cannot be emptied.
Officials note that while not every mosquito carries La Crosse virus, the mosquito species capable of transmitting the disease is found throughout Ross County. Residents are encouraged to remain vigilant throughout mosquito season and take preventive measures to protect themselves and their families.
