What to know about West Nile Virus

West Nile Virus remains a persistent public health concern in Pa., with infected mosquitoes detected across the state during warmer months. It poses seasonal risks to residents, especially in areas with dense mosquito populations and standing water.

Understanding how the virus spreads, where it’s most commonly found and how to protect yourself is key to staying safe.

What is West Nile Virus?

West Nile Virus is the leading mosquito-borne illness in the U.S. It’s transmitted to humans through the bite of an infected mosquito. The virus cycles between birds and mosquitoes, with humans considered “dead-end” hosts — meaning we don’t spread the virus further. Generally, the types of mosquitos that carry the virus are active from dusk until dawn.

What are the symptoms of West Nile Virus?

Most people infected with the virus won’t feel sick. But for those who do, symptoms may include:

• Fever
• Headache
• Body aches
• Fatigue
• Skin rash (in some cases)

In rare instances, it can lead to encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes around the brain and spinal cord), which may cause:

• High fever
• Neck stiffness
• Disorientation
• Muscle weakness
• Seizures

Older adults and individuals with weakened immune systems are at greater risk for severe illness.

Where has West Nile Virus been found in Pa.?

Mosquitoes carrying the virus have been detected in both urban and rural areas throughout the state. Counties with higher populations and more standing water — such as Allegheny, Philadelphia, Lancaster and Dauphin — often report more frequent mosquito surveillance findings.

However, no region is immune, and cases can emerge anywhere conditions are favorable for mosquito breeding.

How to protect yourself from West Nile Virus

The Pennsylvania Department of Environmental Protection (DEP) and local health agencies conduct regular mosquito trapping and testing to monitor West Nile Virus activity. These efforts help identify hotspots and guide public health responses, including targeted spraying and community education.

Even so, preventing mosquito bites is the most effective way to avoid infection. Here are key tips:

• Use insect repellent containing DEET, picaridin or lemon eucalyptus oil
• Wear long sleeves and pants, especially at dawn and dusk
• Eliminate standing water around your home — mosquitoes breed in stagnant water found in:
  • Buckets, tires, flower pots
  • Birdbaths, wading pools, tarps
  • Clogged gutters and pool covers

The Department of Environmental Protection (DEP) also encourages residents to report mosquito breeding sites to local authorities.

What to do if you have symptoms of West Nile Virus

If you start experiencing flu-like symptoms — especially after spending time outdoors during mosquito season — it’s important to take action:

• Monitor your symptoms closely. Most cases of West Nile Virus are mild and resolve on their own, but fatigue and weakness can linger for weeks or even months.
• Get medical attention if symptoms worsen. If you develop severe signs like high fever, neck stiffness, confusion, muscle weakness or vision loss, seek emergency care. These may indicate encephalitis or meningitis, which require hospitalization.
• Rest and hydrate. There is no specific antiviral treatment for West Nile Virus. Supportive care — such as rest, fluids and over-the-counter pain relievers — can help manage symptoms.
• Avoid further mosquito exposure. Stay indoors during peak mosquito hours and use insect repellent to prevent additional bites while recovering.

People over 55, those with chronic conditions like diabetes, cancer or kidney disease, and individuals who’ve received organ transplants are more likely to develop severe illness. If you fall into one of these categories, don’t delay seeking care if you have symptoms.

For the latest updates on West Nile Virus activity in Pa., visit the DEP’s mosquito surveillance page or check the CDC’s West Nile data and maps.