Health Department News Releases

Posted on: June 5, 2017

West Nile Virus identified in Mosquito Sample in Chester County

The Chester County Health Department is informing residents that a mosquito sample collected in East Goshen Township on May 25, 2017 has tested positive for West Nile virus (WNV).


This is the first mosquito sample that has tested positive in Chester County in 2017. The Chester County Health Department sets mosquito traps to collect and test adult mosquitoes for WNV as part of routine surveillance. Traps are placed in highly populated areas, known mosquito breeding areas, and in areas where a resident has previously been identified as having a confirmed case of WNV infection. Traps are also placed in response to complaints from residents regarding high levels of mosquito activity. The Chester County Health Department will continue to monitor these areas as well as surrounding areas and will consider mosquito control activities when appropriate. 


The chances of contracting WNV from an infected mosquito are small and chances of becoming seriously ill are even smaller. However, the Chester County Health Department encourages county residents to “Make you and your home a bite-free zone”, reducing the risk of West Nile virus and other mosquito-borne diseases. Because mosquito-borne diseases are spread through the bite of an infected mosquito, residents can reduce their risk by using insect repellent and other personal protection and getting rid of standing water on their property.


The Health Department advises:

  • Limit outdoor activities at dawn and dusk during warmer months since most types of mosquitoes bite most frequently during these times. Be aware though that some types of mosquitoes bite most frequently during the daytime.
  • Wear long-sleeved shirts and long pants, and socks. Choose clothing that is light colored and made of tightly woven material.
  • Stay in places with air conditioning and window and door screens to keep mosquitoes outside.
  • Sleep under a mosquito bed net if you are overseas or outside.
  • If you choose to use insect repellents, use Environmental Protection Agency (EPA)-registered repellents with one of the following active ingredients: DEET, picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol. Choosing an EPA-registered repellent ensures the EPA has evaluated the product for effectiveness. When used as directed, EPA-registered repellents are proven safe and effective, even for pregnant and breast-feeding women.
    • Always read and follow the product label instructions carefully.
    • Reapply insect repellent as directed.
    • Do NOT spray repellent on the skin under clothing.
    • If you are also using sunscreen, apply sunscreen before applying insect repellent.
  • To protect your child from mosquito bites:
    • Do NOT use insect repellent on babies younger than 2 months old.
    • Do NOT use products containing oil of lemon eucalyptus or para-menthane-diol on children younger than 3 years old.
    • Do NOT apply insect repellent onto a child’s hands, eyes, mouth, and cut or irritated skin.
    • Adults: Spray insect repellent onto your hands and then apply to a child’s face.
    • Dress your child in clothing that covers arms and legs.
    • Cover cribs, strollers, and baby carriers with mosquito netting.
  • Clothing and gear treated with permethrin or permethrin spray for clothing is available for purchase. Read and follow product information carefully to determine if this is a solution for you.
    • Treated clothing remains protective after multiple washings. See product information to learn how long the protection will last.
    • If treating items yourself, follow the product instructions carefully.
    • Do NOT use permethrin products directly on skin. They are intended to treat clothing.
  • To protect your pets:
    • Do NOT use any product on pets unless it is specifically made for pets.

The Health Department also encourages the public to:

  • Cover or empty containers such as trash cans, wading pools, wheelbarrows, and pots.
  • Turn containers upside down when not in use so they don’t collect water.
  • Drill holes in the bottom of recycling containers.
  • Get rid of old tires.
  • Change the water in bird baths every three to five days.
  • Check storm drains, window wells, and underneath leaky faucets for standing water.
  • Clean roof gutters every year.
  • Aerate and/or stock ornamental ponds with fish.
  • Keep swimming pools clean and chlorinated. Make sure that water does not gather on swimming pool covers.
  • Treat a pool of standing water that cannot be drained with Bti products. Bti is a naturally-occurring bacterial product that kills mosquito larvae and is safe for people, pets, aquatic life, and plants. You can find these products at local lawn and garden supply stores.
  • Make sure that window and door screens fit tightly to keep mosquitoes out of your home.
  • Run electric fans nearby when spending time outdoors. Mosquitoes have trouble flying in strong winds.
  • Replace outdoor lights with yellow "bug" lights, which tend to attract fewer mosquitoes than ordinary lights.


For more information on preventing mosquito-borne diseases, visit www.chesco.org/mosquitoes or call 610-344-6490. Chester County residents can be notified about future mosquito control sprays through the following outlets:


The Chester County Health Department is a member of the Environmental Protection Agency’s Pesticide Environmental Stewardship Program. This program requires participants to affirm that environmental stewardship is an integral part of their integrated pest management (IPM) practice, use current, comprehensive information regarding the life cycle of mosquitoes within their IPM program, educate the community on the benefits of IPM, and demonstrate a commitment to pesticide risk reduction activities.