West Nile virus has been detected in a mosquito sample collected in Wynnewood on Aug. 13, making Lower Merion Township the second Main Line community to confirm the virus this summer.

The Montgomery County Office of Public Health identified the positive sample as part of routine surveillance, according to a township public health advisory posted Aug. 19. No human cases of West Nile virus have been reported in Eastern Pennsylvania in 2026, according to CDC data cited by Patch.

The first Main Line detection came in July, when the Delaware County Health Department notified Radnor Township that mosquitoes trapped by the Mosquito-Borne Disease Control Program in Racke Park carried the virus, Main Line Media News reported. That finding meant mosquitoes in the trap tested positive, not that any person was infected, Radnor officials said at the time.

29 positive samples countywide

Montgomery County has recorded 29 positive mosquito samples as of mid-August, according to Pennsylvania Department of Environmental Protection data. The county's Office of Public Health monitors mosquito activity throughout the region and may conduct pesticide spraying if traps test positive for viruses that threaten public health. Officials must issue a press release at least 48 hours before any spray.

Lower Merion officials attributed the elevated mosquito activity to a summer of heavy rain, heat and humidity. The conditions are ideal for breeding, the township said in its Aug. 19 press release, and residents should take precautions.

What residents should do

The township is asking residents to:

  • Remove or drain standing water from gutters, drains, tires and containers
  • Check that screens on doors and windows are in good condition
  • Avoid outdoor activities from dusk to dawn, when mosquitoes are most active
  • Wear long-sleeved shirts, long pants and socks if outside during peak hours
  • Use mosquito repellent with an EPA registration number on the label

West Nile virus spreads through bites from infected mosquitoes. Symptoms include fever, headache, body aches, vomiting, diarrhea and rash. Severe cases can affect the central nervous system. Older adults and people with weakened immune systems face the highest risk.

Residents can sign up for ReadyMontco alerts to receive notifications about mosquito spraying and other public health events. Those with questions can call the Montgomery County Office of Public Health at 610-278-5117.