West Nile Virus

Mosquito Control and why it's Important to YOU



What is West Nile Virus (WNV)?


WNV is a mosquito-borne virus that can cause fever, encephalitis (inflammation of the brain), or meningitis (inflammation of the lining of the brain and spinal cord).

How do people get WNV?


WNV is most commonly spread through the bite of an infected mosquito. WNV can be spread through blood transfusions, organ transplants, and from mother to baby during pregnancy, delivery, or breastfeeding but this is very rare. It is not transmitted from person to person, or from person to animal.

What are the symptoms of WNV?


Most people (70-80%) infected with WNV do not develop any symptoms. 

If present, WNV symptoms usually appear 2-14 days after the mosquito bite. Approximately 1 in 5 people infected will develop a fever and possibly headache, body aches, joint pain, vomiting, diarrhea, or rash. Most people with these symptoms recover completely, but fatigue and weakness can last for weeks or months.

Less than 1% of people infected will develop serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues). Recovery from severe illness may take weeks or months. Some of the neurologic effects may be permanent. Only about 10% of people who develop neurologic infection due to WNV will die.

Serious illness can occur in people of any age. However, people over 60 years of age are at the greatest risk for serious illness. People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants are also at greater risk for serious illness.

See your health care provider if you have symptoms of WNV.

Who is at risk for WNV infection?


Anyone living in an area where mosquitoes are infected with WNV is at risk. WNV has been detected in all states except Alaska and Hawaii. The risk of infection is highest for people who work outside or participate in outdoor activities because of greater exposure to mosquitoes.

Is there a vaccine or treatment for WNV infection?


There is no vaccine or specific treatment for WNV infection.

People with mild symptoms of WNV infection usually recover on their own. Over-the-counter pain relievers can be used to reduce fever and relieve some symptoms. People with severe illness usually need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.
wnv stopmosquitoes_456px

How can I prevent WNV?

Make you and your home a Bite-Free Zone to prevent WNV and other mosquito-borne diseases.


What is the Chester County Health Department doing to prevent WNV?


  • Provides educational materials. Call 610-344-6490 to request materials.
  • Provides community education. Request a presentation or participation at a community event
  • Responds to complaints of standing water- Chester County Health Department enforces County regulations requiring property owners to dump and drain sources of standing water (ex. tires, pools, containers) which mosquitoes use for breeding. Citations may be issued for failure to comply.
  • Identifies bodies of water containing mosquito larvae.
  • Sets mosquito traps to collect and test adult mosquitoes for WNV – 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.
  • Uses U.S. Environmental Protection Agency-approved products (BtiBs, or Methoprene) to kill mosquito larvae in bodies of standing water that cannot be drained.
  • Uses U.S. Environmental Protection Agency-approved products (Permanone or DeltaGard) to kill adult mosquitoes in areas that have high mosquito activity and multiple mosquito samples testing positive for WNV- Spraying is done as a last resort after exhausting all other mosquito control strategies. 
    • The Chester County Health Department uses a truck-mounted sprayer to apply 1.5 ounces of the mosquito control product per acre of land. Sprays are conducted after sunset, when mosquitoes are most active and bees have returned to their hives. Sprayers are turned off near bodies of water and apiaries to protect aquatic life and bees. The Chester County Health Department also notifies beekeepers and residents who are listed as hypersensitive in a designated spray area prior to conducting a spray. People who are concerned about exposure to mosquito control products can reduce their potential for exposure by staying indoors with children and pets when their neighborhood is being sprayed. Because the mosquito control spray becomes inactive in just a few hours or with sunshine, it is not necessary to wash off outdoor furniture or playground equipment before use.
    • 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.
  • Investigates reports of WNV illness in residents.

How can I find out when a mosquito control spray is being conducted in my neighborhood?


The Chester County Health Department notifies residents of sprays at least 48 hours ahead of time through the following channels:
  • News releases sent to the media, legislators, municipalities, etc.
  • Public Health Updates- E-mail updates that residents can sign up for.
  • Chester County Health Department website.
  • Chester County Health Department Facebook and Twitter.
  • Residents in a designated spray area who are listed as hypersensitive are contacted directly by the Chester County Health Department.

People who are concerned about exposure to mosquito control products can reduce their potential for exposure by staying indoors when their neighborhood is being sprayed.

For more information, call 610-344-6752 or email cchd@chesco.org

Links