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Public Works - Wastewater/Storm

Mosquito Sampling Program: West Nile Virus

West Nile virus infection has been confirmed in several birds in Washington and Multnomah counties. There have been no confirmed infections in humans in western Oregon. Human illness from West Nile virus is rare, even in areas where the virus has been reported. The chance that any one person is going to become ill from a mosquito bite is low. However, concern for one's personal health has many asking questions about how best to prepare and protect themselves from West Nile virus.

In response to public concern Tigard's staff has initiated the Mosquito Sampling & Monitoring Program in which staff members inspect storm water ponds, local wetlands and streams, and the public drainage system for mosquito larva. In addition, Tigard has contracted with Washington County Mosquito Control to perform larvicide mosquito control at city owned wetlands; and maintains relationships with the Department of Health and Human Services, Washington County and other local cities to track possible cases of West Nile virus. Please note, the city does NOT perform mosquito control on private properties.

To learn more about West Nile virus visit the Centers for Disease Control (CDC) website at: http://www.cdc.gov/westnile.

Frequently Asked Questions

Am I at risk of becoming infected with West Nile?
Human illness from West Nile virus is rare, even in areas where the virus has been reported. The chance that any one person is going to become ill from a mosquito bite is low.

Will the City of Tigard and/or the County spray for mosquitoes?
Local and state health experts have agreed that widespread chemical spraying is not the answer. Rather, the City of Tigard will use a progressive level of control strategies to control mosquitoes primarily education, (habitat reduction), and larvae controls. The City of Tigard will not perform larvae control on private property. Larvacide is available off-the-shelf from local vendors for home owners who wish to use it. The City of Tigard will not spray for adult mosquitoes unless directed to by the Washington County Health Division.

Will the City of Tigard help me with mosquito control on my property?
Yes, the City of Tigard will be glad to meet with you at your site to discuss your concerns regarding mosquitoes and/or the West Nile virus (WNV). We can offer you suggestions regarding mosquito habitat on your property, we can take samples from water sources to have mosquito larvae identified (this is valuable as there are only four types of mosquitoes in our area that have a high probability for carrying the virus). The City of Tigard will not spray for adult mosquitoes unless directed to by the Washington County Health Division.

What is being done to monitor and control mosquitoes that may be carrying the West Nile virus on public properties such as parks, wetlands, catch basins and storm water quality facilities?
The City of Tigard Public Works and other cities and agencies in Washington County are working with the Washington County Department of Health and Human Services to monitor the public properties mentioned above.

If mosquitoes with a high potential to carry the West Nile virus are detected, the City of Tigard will use a progressive level of control strategies to control mosquitoes primarily education, (habitat reduction), and larvae controls. The City of Tigard will not perform larvae control on private property. The City of Tigard will not spray for adult mosquitoes unless directed to by the Washington County Health Division.

Are storm water catch basins significant breeding grounds for mosquitoes that carry the West Nile virus?
Any standing water can provide breeding grounds for mosquitoes that carry West Nile virus. Many of the catch basins in the City of Tigard are designed to trap pollution and hold a small amount of storm water after a rainfall event. These catch basins can be breeding grounds for mosquitoes that carry West Nile virus. The City of Tigard Public Works and other cities and agencies in Washington County will be working with the Washington County Department of Health and Human Services this summer to sample water from these types of catch basins in the urban area to monitor them for the presence of mosquitoes carrying West Nile virus, and perform larvae control if needed.

Are storm water ponds and swales significant breeding grounds for mosquitoes that carry the West Nile virus?
Stormwater ponds and swales are designed to filter pollution from rain-water runoff and reduce flooding. Most of the facilities that have been built in residential and commercial developments since 1990 are designed to drain within a few days, which prevent mosquito larvae from completing their development.

However, some stormwater ponds and swales are designed to hold water most of the year or may retain small pools of water. These facilities offer habitat for many of species of frogs, birds, fish and aquatic insects that feed on mosquitoes and their larvae. The City of Tigard Public Works and other cities and agencies in Washington County are working with the Washington County Department of Health and Human Services to inventory and evaluate the maintenance of these facilities to reduce mosquito breeding habitat and improve the habitat for natural mosquito predators.

The City of Tigard Public Works and other cities and agencies in Washington County are working with the Washington County Department of Health and Human Services to monitor these facilities for the presence of mosquitoes carrying West Nile virus are detected, the Washington County Department of Health and Human Services will provide guidance to local communities on more aggressive control measures including the application of biological larvcide controls.

Are wetlands a significant breeding ground for mosquitoes with the West Nile virus?
Although wetlands can provide habitat for mosquitoes, typical water conditions and natural predators found in healthy wetlands deter mosquito use and minimize larval success if egg laying occurs. Predators including other aquatic insects, amphibians, and birds feed on any mosquitoes present. Wetlands are a critical element in a healthy ecosystem that benefits people, water quality and wildlife. Wetlands clean and slowly release rainwater and provide flood protection and wildlife habitat. Many wetlands recharge groundwater critical for local drinking water supplies and prevent streams from drying up during the summer. We will not eliminate mosquitoes by draining wetlands. We could actually increase the mosquito population if their natural predators are destroyed by draining a wetland. Many mosquito species need only a small puddle or depression in which to breed.

Are streams and rivers significant breeding grounds for mosquitoes that carry the West Nile virus?
Under normal circumstances, mosquitoes cannot breed successfully in flowing water, and therefore streams and rivers can only produce mosquitoes when they dry up and leave shallow, stagnant puddles in the stream bed or in backwater areas. Streams and rivers provide good habitat for predators that feed on mosquitoes and mosquito larvae.

I live near a greenway and/or wetland and worry about my family's safety.
We will never be able to eliminate all habitats for mosquitoes and not all mosquitoes are carriers of the virus. Greenways and wetlands provide numerous health and quality of life benefits. They clean pollution from air and water and reduce flooding and erosion. The use of chemical controls can affect the environment and human health and have limited success unless carefully applied by licensed pesticide applicators. Application of pesticides to wetlands, streams and other waterways can not only affect the environment and, ultimately, human health, but may be illegal under state and federal law.

Local and federal health experts recommend the best personal protection is to reduce mosquito habitat, prepare your home and take personal protection measures.
 

Helpful Hints

Below are some helpful hints that you and your family can do to reduce exposure to the West Nile Virus:

Reduce Mosquito Habitat
Mosquitoes lay their eggs in standing water. The eggs only need a few ounces of water to grow into adults. Reduce mosquito habitat by:
  • Eliminate places where water can stagnate in containers such as buckets, flowerpots and tires.
  • Change water at least once a week in birdbaths and wading pools.
  • Clean clogged rain gutters, and put mosquito screens on rain barrels.
  • Dispose of old tires or cover them so they do not collect water.
Prepare Your Home
  • Put tight-fitting window screens on all your windows, and repair rips or tears in existing screens.
  • Consider adding a screen door to outside doors that are often left open.
Personal Protection
We will never be able to eliminate all mosquitoes. Personal protection is a way to avoid getting bitten. When mosquitoes are out, particularly at dusk:
  • Wear long sleeves and long pants.
  • Consider wearing insect repellent that contains DEET or eucalyptus. Read repellent instructions carefully. Repellent should not be applied to children under the age of two.

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