Pennsylvania health officials are reminding residents to take routine precautions against mosquito bites after the first West Nile virus-positive mosquito pools of 2026 were detected in nine counties across the state.
The Pennsylvania Department of Health announced that mosquito samples collected in Allegheny, Beaver, Bucks, Lycoming, Monroe, Northumberland, Pike, Tioga and York counties tested positive for West Nile virus through the state’s seasonal surveillance program. The findings indicate the virus is circulating in Pennsylvania as the summer mosquito season gets underway.
Health officials emphasized that the detection of infected mosquitoes is expected during warmer months and does not mean widespread illness is occurring. Human cases of West Nile virus are most commonly reported between July and September, with risk continuing until the first hard frost of the season.
Most people infected with West Nile virus never become sick. According to the Department of Health, about 80% of infections cause no symptoms. Roughly 20% of infected individuals may develop a flu-like illness that can include fever, headache, fatigue, body aches or a rash.
Serious illness is uncommon. Less than 1% of infections develop into severe neurological disease, such as meningitis or encephalitis. Older adults and people with weakened immune systems face a higher risk of severe complications.
Pennsylvania reported 80 human West Nile virus cases during the 2025 season, including 58 cases involving neurological illness and 22 cases of less severe disease. Cases were reported from 22 counties.
West Nile virus remains the most commonly reported mosquito-borne disease acquired within Pennsylvania. The virus is transmitted through the bite of infected mosquitoes and is not spread through casual contact between people.
State officials are encouraging residents to reduce mosquito exposure by using insect repellent, wearing long sleeves and pants when practical, and eliminating standing water around homes where mosquitoes can breed.
The Department of Health also reminded medical providers to consider West Nile virus and other mosquito-borne illnesses when evaluating patients with unexplained fever, meningitis, encephalitis or other compatible symptoms during the summer months.
In addition to West Nile virus, Pennsylvania monitors for several other mosquito- and tick-borne viruses, including Jamestown Canyon virus, La Crosse encephalitis virus and the rare Powassan virus, which is transmitted by ticks.
Additional mosquito surveillance will continue throughout the summer as state officials monitor virus activity and potential risks to public health.
Source: PA. Dept of Health