Philadelphia health officials are warning residents after West Nile virus was found in mosquitoes in Northeast Philadelphia earlier this month.

Mosquitoes in a Butler County community have tested positive for West Nile virus. The Mercer County Conservation District says the mosquitoes collected in Franklin Township were the first sample to test positive for the virus in Butler County in 2025.

City health officials instructed Philadelphia medical providers to check patients for West Nile virus and other mosquito-borne illnesses and immediately report cases.