Mosquitoes carrying West Nile Virus have been found in Lower Merion Township for the first time this season, prompting health officials to urge residents to dump standing water and cover up at dusk.

The Montgomery County Office of Public Health confirmed the virus in a mosquito sample collected Aug. 13 in the Wynnewood area, according to an advisory shared by the township. No human cases of West Nile Virus have been reported in Eastern Pennsylvania this year, per CDC data.

The detection is one of 29 positive mosquito samples found across Montgomery County as of Aug. 18. The county's Office of Public Health attributed the elevated activity to a rainy, hot and humid summer that created ideal breeding conditions for mosquitoes.

Montgomery County declared a Code Red Hot Weather Emergency Aug. 6–8 when the heat index was forecast to exceed 100 degrees. Those same conditions accelerate mosquito breeding. According to the county health office, even a small amount of standing water left for five days can produce thousands of mosquitoes.

Who's most at risk

West Nile Virus spreads through the bite of an infected mosquito. Most people experience no symptoms, but the illness can cause fever, headache, body aches and rash. Severe cases can affect the central nervous system. People over 50 and those with weakened immune systems face the highest risk of serious illness, according to the Pennsylvania Department of Environmental Protection. There is no vaccine or specific treatment.

What residents should do

The county recommends:

  • Remove or drain standing water from gutters, tires and containers.
  • Check that window and door screens are intact.
  • Avoid outdoor activities from dusk to dawn, when mosquitoes are most active.
  • Wear long sleeves, long pants and socks outdoors in the evening.
  • Use mosquito repellent with an EPA registration number.

If the Office of Public Health determines spraying is warranted, a press release will be issued at least 48 hours in advance. Residents can sign up for ReadyMontco alerts to receive spray notifications by phone or email.

Residents with questions can call the Montgomery County Office of Public Health at 610-278-5117.