West Nile Virus FAQs

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Q. What is West Nile Virus?

A. According to the Centers for Disease Control and Prevention, West Nile virus (WNV) is the leading cause of viral encephalitis in the United States. WNV was first detected in the United States in 1999 in New York City and has now been reported in every state except Hawaii, Alaska and Oregon. It causes seasonal epidemics of West Nile fever and a more severe illness, West Nile Neuroinvasive disease. West Nile virus is transmitted to humans and animals through the bite of an infected mosquito. Mosquitoes become infected with WNV when they feed on infected birds.


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Q. How serious is the current illness outbreak caused by West Nile virus?

A. Serious enough that those in the DFW area should take preventive steps now. One-quarter of all WNV cases in the United States are in Dallas County. Most people exposed to this virus do not develop symptoms. Some will develop moderate flu-like symptoms. In its more severe form, the virus can cause high fever, paralysis, coma, and rarely, death.

Q. What Are the Symptoms of WNV?


A. Individuals respond differently to the virus and may experience a range of symptoms or no symptoms at all.


No Symptoms: Approximately 80% of people (about 4 out of 5) who are infected with WNV will not show any symptoms at all.


Milder Symptoms: West Nile Fever (WNF): Up to 20% of the people who become infected have symptoms such as fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though even healthy people have become sick for several weeks.

Severe Symptoms: Also called neuroinvasive disease (WNND). About 1 in 150 people infected with WNV will develop severe illness, including high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent. On rare occasions, WNND results in death.

Q. What personal preventive measures are effective against West Nile Virus?

A. To reduce exposure to West Nile virus:

  • Use an approved insect repellent every time you go outside and follow the instructions on the label. Approved repellents are those that contain DEET, picaridin or oil of lemon eucalyptus.
  • Regularly drain standing water, including water collected in empty cans, tires, buckets, clogged rain gutters and saucers under potted plants. Mosquitoes breed in stagnant water.
  • Wear long sleeves and pants at dawn and dusk when mosquitoes are most active.
  • Use air conditioning or ensure all doors and windows are screened to keep mosquitoes from entering the home.

Q. What about spraying to control mosquito populations?

A. Land-based and aerial spraying have been shown to be effective in controlling West Nile virus. Carrollton has used land-based spraying to control mosquitoes for over 20 years.

Q. Why is aerial spraying necessary now?

A. Aerial spraying is the recommended approach of doctors and medical groups at the local, state and federal level to substantially reduce the adult mosquito population.

Historically, aerial spraying is part of the County’s overall plan and is used to effectively contain other outbreak circumstances in the US, including Dallas in 1966. Aerial spraying can distribute pesticide faster, more effectively than truck-mounted operations. The compound applied here, Duet, is similar to the pesticide used in our truck-mounted spraying operations, as well as to those used safely in other areas, including Sacramento County, New York, Massachusetts, and Florida. Spraying is done at night to reduce impact on people and beneficial insects. Duet is a light-sensitive chemical that breaks down quickly in sunlight or water, with no documented impact to human health.

For these reasons, the Carrollton City Council has chosen to participate in a regional aerial spraying program that will cover the entire City of Carrollton.

Q. What to expect from aerial applications?

A. The Texas Department of State Health Services (DSHS) contracts with Clarke, a private environmental products and services company, and will conduct aerial applications of mosquito control products in Dallas County. Up to five airplanes will fly at approximately 300 feet in the air at 170 mph, utilizing GPS technology to ensure effective coverage. Airplanes are to be ready to begin spraying on Thursday night, with a repeat application on a succeeding night. Inclement weather might delay the process. The results of ongoing monitoring may necessitate additional applications.

The State is covering expenses associated with aerial spraying through various disaster management funds. Applications in Carrollton are estimated at $100,000.

Q. How will notification be provided?


A. Public Notification Outreach:

  • News releases sent to media and homeowners organizations
  • Media outreach (City to provide spokespersons to media as needed)
  • All information posted on cityofcarrollton.com, including areas to be sprayed and Aerial Application FAQ
  • Duet chemical FAQ
  • Social Media: All information posted on the City’s social media sites
  • Signs posted in high traffic areas in the spraying zones
  • Post signs at recreation centers and libraries
  • Continue to encourage media usage of the City’s prevention PSA “Fight the Bite” English version: http://www.youtube.com/watch?v=tCped8grjGc Spanish version: http://www.youtube.com/watch?v=jkZWV_-jyts



Duet Adulticide FAQs

Q. What is Duet?

A. Duet is the name of a public health mosquito control product. It has two active ingredients: Sumithrin and Prallethrin. They are formulated to mimic the natural pyrethrins that are extracted from chrysanthemum flowers. Duet was registered by the U.S. EPA for use for public health applications in 1995 to help control adult mosquito populations.

Q. Does Duet pose a health risk to humans?

A. The U.S. EPA has reviewed Duet and approved it for both ground and aerial application in outdoor residential, recreational areas and other areas. Sumithrin, the active ingredient in Duet products, has been approved for use for outdoor mosquito control since 1987. Sumithrin is also a key ingredient used in products for the pet industry, in household insecticide products for flea and cockroach control, and in medicated lice control shampoos for humans. The second active ingredient in Duet is Prallethrin. It was developed in the 1980s as an alternative to pyrethrins and is used widely in pest control products throughout the world.

Q. Will this product harm my children and/or pets?

A. No. The U.S. EPA has approved Duet for use in outdoor residential and recreational areas. Duet is applied at extremely low dosage rates -less than an ounce per acre. An acre is equivalent to approximately a football field. Such low rates mean there is very low exposure even if present during or immediately after the application is made. For added safety it's recommended for children and pets to wait until any application is dry before going into treated areas.

Q. Can my children and/or pets play outside after the application? How long after the application can we go outside?

A. There are no re-entry precautions or limitations for Duet. It degrades rapidly in the environment and does not bio-accumulate, which means it is not passed through the naturally occurring food chain. Each state may make particular recommendations when communicating to their public to ensure that common sense steps are taken during and after spraying.

Q. Will Duet harm my unborn baby?

A. A number of studies have been conducted to determine the teratogenic effects on unborn babies. No teratogenic effects have been associated with either active ingredient in the product. Duet is applied at extremely low dose rates and minimal precautions can eliminate or at least drastically minimize exposure to any insecticide that is sprayed to further reduce concerns.

Q. Will this chemical harm the finish on my car and/or house?

A. The ingredients of Duet are not corrosive or staining and therefore should cause no chemical harm to the finish of a car and/or house.

Q. Do vegetables and fruits need to be harvested before the spraying? Or is there a certain amount of time I need to wait? Is rinsing with water sufficient?

A. Duet degrades quickly in the environment and will not have an accumulative effect. It is good common sense to always rinse fruits and vegetables with water as a precautionary measure.

Q. Do I need to cover my fish pond prior to a spraying?

A. The spraying should not pose a risk for a healthy pond under sound environmental conditions. If an individual does have a concern, covering the fish pond as an added precaution would be the best approach.

Q. Do I need to cover my swimming pool or wait before re-entering the water?

A. The chemical used in spraying (Duet) breaks down quickly in water and sunlight. You do not need to cover your pool or bring in patio furniture; and you do not need to wait before using the pool again.

Q. Do horses and livestock need to be sheltered during the application?

A. Horses and livestock should not be adversely affected by applications of Duet. This product breaks down quickly through sunlight and does not bioaccumulate, meaning it will not affect the livestock.

Q. How does Duet affect non-target insects?

A. Because of the manner in which Duet is applied and the time of day it is applied, it should not impact beneficial insects. Duet is applied in small droplets, which degrade quickly in the environment. Since the product must impinge or strike a mosquito to have an effect, it is sprayed at night when mosquitoes are actively flying. This happens to be when other insects, such as bees and butterflies, are not active.

Q. How does Duet affect the environment?

A. The U.S. Environmental Protection Agency has determined that Duet can be applied by truck or aircraft in outdoor residential and recreational areas, including vegetation surrounding parks, woodlands, swamps, marshes, overgrown areas and golf courses. It breaks down quickly in sunlight to primarily carbon dioxide, which is found in the air that humans exhale. It also breaks down into benzoic acid, which according to the EPA poses little or no risk to soil, plants and the environment in general, if applied in the recommended amounts.

Q. How is Duet applied?

A. Generally, Duet is applied at an ultra low volume in an extremely fine mist of tiny drops, where the average droplet size is 17 microns. This amount is smaller than the size of a pinhead.

Q. How much is typically applied?

A. Duet is applied in very low dosages, from less than half an ounce to a little more than one ounce of formulated product per acre (.41 to 1.23 fl oz/ac). This is approximately a teaspoon of formulated product on an area the size of a football field.

Q. Will this eliminate our mosquito population?

A. Mosquito populations are not static. Instead, they are constantly regenerating. Source reduction (reducing unnecessary standing water), surveillance, and larviciding (controlling the mosquito population before adulthood) are not alone sufficient to control mosquito populations. To control the spread of disease, adulticiding, or spraying, is necessary. Duet is effective in controlling disease-spreading mosquitoes. A specific problem area is identified and sprayed, but the spraying in this targeted area is not reaching an entire habitat of mosquitoes. Sometimes mosquitoes move into the spray zone from outside of it after an application is made, which is called re-infestation, (i.e., they drift in on wind currents from upwind areas that have not been treated). When mosquito re-infestation occurs, additional sprayings must be considered to control the spread of the vector of West Nile Virus, mosquitoes. Effectively controlling an adult mosquito population through spraying also depends on a number of external factors, including timing, the level of re-infestation, methodology used during the spraying, and weather conditions.

Q. Do I have to go indoors during the applications?


A. No. The U.S. EPA has approved Duet for use in outdoor residential and recreational areas.