[Note: we have often wondered how a pesticide can “prevent” a virus when it can’t even “prevent” mosquitoes. Note on the active ingredient deltamethrin from Wikipedia: “Resistance has been characterised in several insects, including important vectors of malaria like the mosquito Anopheles gambiae as well as non-disease carrying pests like bed bugs.” That is one of the problems with any pesticide: insects can become resistant to anything! Because of acquired resistance, Permanone (previously used in Chesco) could not be used in Miami during the recent Zika scare. If you live in the spray area, see how you can help us here.]

from Chesco Health Department pdf

West Chester, PA – The Chester County Health Department will conduct a mosquito control treatment spray in portions of Parkesburg (see map below). The treatment is scheduled for Thursday, August 9th from 8:00 pm to 11:30 pm. The rain date for this event is Monday, August 13th from 8:00pm to 11:30pm.

The Chester County Health Department conducts mosquito control treatment in areas with high levels of mosquito activity and where multiple mosquito samples have tested positive for West Nile Virus (WNV). After exhausting all other available mosquito control strategies, spraying is conducted to reduce residents’ risk of WNV infection. Anyone living in an area where mosquitoes are infected with WNV is at risk, but the risk of infection is highest for people who work outside or participate in outdoor activities. Less than 1% of people infected will develop serious illness. While serious illness can occur in people of any age, people over 60 years of age, people who have received organ transplants, and people with certain medical conditions such as cancer, diabetes, hypertension, and kidney disease are at the greatest risk for serious illness.

The Chester County Health Department uses a truck-mounted sprayer to apply .66 ounces of U.S. Environmental Protection Agency-approved product (DeltaGard) per acre of land….

read more in the Chesco Health Department pdf