West Nile

Don't be bugged by West Nile virus

This year, the Delaware County Health Department’s Environmental Health Division will be overseeing the Mosquito-borne Disease Control Surveillance and Control program throughout Delaware County. This program is staffed by a Coordinator and Vector Technicians are responsible for vector control throughout the county.

What is West Nile virus?

West Nile encephalitis describes a brain infection caused by West Nile virus (WNV). Cases occur primarily in the late summer or early fall, although mosquito season is usually April through October. People can get infected from the bite of certain species of mosquitoes that are infected with the virus. Although most infections are mild, serious illness can occur. In 2011 WNV was detected in 95 mosquito samples in Delaware County. There was NO human case of WNV in Delaware County last year. According to the State D. E. P., WNV was detected in 251 mosquito samples in Delaware County in 2020. There was NO confirmed human case of WNV in Delaware County last year.

What happens if mosquitoes infected with West Nile virus are found in my area?

If mosquito surveillance and testing show that there is a threat to human health, Delaware County Health Department may initiate a spray to control adult mosquitoes. Delaware County does not conduct nuisance mosquito control or take requests from the public for mosquito spraying.

Will my neighborhood be sprayed for mosquitoes?

Spraying for adult mosquitoes (adulticiding) is just one part of any mosquito management program. Mosquito surveillance, which is done by setting up mosquito traps and looking for areas where mosquitoes breed, and larvaciding (treating mosquito eggs) typically make up about 95% of the program, however, adulticiding is called for at certain times.

Adulticiding is based on data that is collected by trapping mosquitoes and is extremely important when deemed necessary. The Delaware County Department of Health, under a grant from the Pennsylvania Department of Environmental Protection (DEP), along with the Penn State Cooperative Extension, will be conducting daily surveillance by setting up mosquito traps throughout Delaware County from spring until fall. If high numbers of mosquitoes are detected and/or mosquitoes test positive for WNV, DCHD, in consultation with PA DEP the Penn State Cooperative Extension and county and municipal officials, may decide that adult spraying is necessary to protect the health of the general public. All truck-mounted spray events will be planned at least 48 hours in advance.

Please see our DCHD Mosquito/West Nile spraying and treatment alerts website for up to date information about spraying activities in Delaware County.      

Positive bird findings do not present an immediate need for spraying. The testing of birds simply helps us to determine that WNV is present somewhere in the area but does not identify the specific location where the bird contracted the virus. Once a bird has tested positive for WNV, surveillance is enhanced in that general area to test for mosquitoes carrying the virus.

What can I do to reduce my risk of WNV?

Residents can take a few simple steps around their homes to reduce the risk of contracting WNV. Mosquitoes need water to breed, so if you eliminate their breeding spots you reduce their numbers. Even just a small amount of standing water can become home to many mosquitoes in as few as four days.

What should I do if I find a dead bird during WNV season?

The West Nile virus infects certain wild birds. The infected birds, especially crows, are known to get sick and die from the infection. Reporting of dead birds is a good way to check for West Nile virus activity in the environment. The Pennsylvania Dead Bird Surveillance program for West Nile virus relies on Commonwealth citizens to report and submit certain dead birds seen around their property or elsewhere to their West Nile County Coordinators. Since the virus was detected in New York City in 1999, thousands of dead birds have been submitted for testing by citizens in the northeastern US.

Pennsylvania residents are strongly encouraged to report selected species of dead birds on-line via the Internet. The Pennsylvania West Nile Virus Control Program will only collect Corvids(crows), Raptors and Jays beginning June 1. Corvids include crows and ravens. Raptors include eagles, falcons, hawks, buzzards and owls. Blue jays are included in the Jay group.

Residents should take the following steps when they see a dead bird:

To report dead bird sightings, you can call the Delaware County Health Department Wellness Line at (484) 276-2100 and we will submit the information for you.

The Pennsylvania Department of Environmental Protection is collecting 5 birds per week from each county for testing for West Nile Virus from June 1 through October 1, or until the season ends.

Avoid bare-hand contact when handling dead birds. Use rubber gloves when handling a dead bird.

If you do not have gloves, insert your hand into a plastic bag, grasp the bird carefully and invert the bag over the bird. Each bird should be placed in tied plastic bag, and then placed inside a second tied bag.

If you are not submitting the bird for testing, the bagged bird can be placed in the trash.

Wash hands thoroughly with soap and water after discarding the dead bird.

Pennsylvania Hypersensitivity Registry

This registry, which is maintained by the Pennsylvania Department of Agriculture (PDA), is a list of people who have been verified by a physician to be excessively or abnormally sensitive to pesticides. Commercial and public pesticide applicators must contact anyone on the registry whose listed location is within 500 feet of a pesticide application site. By having prior notification, the sensitive individual can take appropriate precautions.

PDA will send, by mail, the registry to each licensed commercial/public pesticide application business. The registry is now published twice a year in March and July. A person will not be considered included on the registry unless their name appears on a current registry. A request for listing on the registry must be received by PDA at least two months before an effective date.

For more information or an application, please call PDA at 717.787.4392 or visit What is the Pesticide Hypersensitivity Registry?

For more information on West Nile virus, please go to the following links:

The Pennsylvania State University

Pennsylvania Department of Environmental Protection

Centers for Disease Control and Prevention (CDC)

For more information on Delaware County's WNV Program, please call:

The Delaware County Health Department Wellness Line (484) 276- 2100.

West Nile Web Links:

Link for CDC Fact Sheet

What is the Pesticide Hypersensitivity Registry?

PA Department of Health: Vectorborne Diseases

PA Department of Health: Mosquito-borne Diseases

For more information and assistance, the Delaware County Health Department Wellness Line is available 24 hours a day, 7 days a week. In addition to responding to phone calls, the Wellness Line also responds to email inquiries.

Phone: (484) 276-2100 (Available 24/7)
Email: DelcoWellness@co.delaware.pa.us

Contact Us

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About Delaware County

Delaware County, presently consisting of over 184 square miles divided into forty-nine municipalities is the oldest settled section of Pennsylvania.

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