West Nile Virus Activity Soars In Eastern PA

Rates of West Nile Virus are growing steadily throughout the greater Philadelphia area and much of Pennsylvania, placing the region at significant risk to the mosquito-born illness, health officials said.

No humans have tested positive for West Nile in Pennsylvania yet in 2025, though the Pennsylvania Department of Environmental Protection said it's been detected in nearly every single one of the state's counties, including all of the greater Philadelphia area. The state classifies the current risk as "very high" on its "Skeeter Meter."

"This means that West Nile virus activity has been found very frequently in mosquitoes in PA," state officials said. "It’s important to control mosquitoes around your home."

Here are the rankings for southeastern Pennsylvania counties for the number of positive West Nile samples collected, according to state statistics:

• Bucks: 4th
• Montgomery: 9th
• Delaware: 11th
• Philadelphia: 12th
• Chester: 15th

Another round of chemical spraying will take place Monday night in Pottstown at Riverfront Park as authorities target areas where samples have confirmed the presence of the virus. Similar spraying events were held in Fairmount Park in Philadelphia and elsewhere around the region over the weekend.

Spraying has become common in recent years as mosquito activity and West Nile Virus have spread more widely. While there are a few factors in play, climate change is the overwhelming cause of the increase, according to scientists and the U.S. Environmental Protection Agency. Shorter winters and longer summers give mosquitoes more time to breed, and more severe storms create larger areas of standing water, which mosquitoes need to breed.

Local health officials offer the following tips to stay safe and to eliminate mosquito breeding areas:

• Wear protective clothing such as long pants, long sleeve shirts, and socks
• Spray permethrin, an insecticide product, on clothing, shoes and gear, but not directly on your skin
• Mosquitoes will breed in any stagnant water that stands for five or more days, so it's important to identify and eliminate all sources of standing water
• Dispose of tin cans, plastic containers, ceramic posts or similar water holding containers
• Pay special attention to discarded tires that may have collected water
• Drill holes in the bottom of recycling container that are left outdoors
• Have clogged roof gutters cleaned on an annual basis, particularly if the leaves from surrounding trees have a tendency to block drains
• Turn over plastic wading pools when not in use
• Turn over wheelbarrows and do not allow water to stagnate in birdbaths
• Aerate ornamental pools or stock them with fish
• Keep swimming pools clean and chlorinated as a swimming pool that is left untended becomes a source of mosquito breeding