Frequently Asked Questions:

What is West Nile virus?

West Nile Virus is a flavivirus commonly found in Africa, West Asia, and the Middle East. It is closely related to St. Louis encephalitis virus which is also found in the United States. The virus can infect humans, birds, mosquitoes, horses and some other mammals.

What are the symptoms of West Nile virus (WNV) infection?

Infection with WNV can be asymptomatic (no symptoms), or can lead to West Nile fever or severe West Nile disease.

It is estimated that about 20% of people who become infected with WNV will develop West Nile fever. Symptoms include fever, headache, tiredness, and body aches, occasionally with a skin rash (on the trunk of the body) and swollen lymph glands. While the illness can be as short as a few days, even healthy people have reported being sick for several weeks. The symptoms of severe disease (also called neuroinvasive disease, such as West Nile encephalitis or meningitis or West Nile poliomyelitis) include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. It is estimated that approximately 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease. Serious illness can occur in people of any age, however people over age 50 and some immunocompromised persons (for example, transplant patients) are at the highest risk for getting severely ill when infected with WNV.

Most people (about 4 out of 5) who are infected with West Nile virus will not develop any type of illness (an asymptomatic infection); however you cannot know ahead of time if you'll get sick or not when infected.

Can I get West Nile Virus from a dead crow?

No, People become infected by the bite of a mosquito infected with West Nile virus. There is no evidence that a person can get the virus from handling live or dead infected birds. However, you should avoid using your bare hands when handling any dead animals.

What can I do to reduce my risk of becoming infected with West Nile virus?

Here are preventive measures that you and your family can take: Protect yourself from mosquito bites:

Apply insect repellent to exposed skin. Generally, the more active ingredient a repellent contains the longer it can protect you from mosquito bites. A higher percentage of active ingredient in a repellent does not mean that your protection is better—just that it will last longer. Click here for more on insect repellent active ingredients. Choose a repellent that provides protection for the amount of time that you will be outdoors.

• • Repellents may irritate the eyes and mouth, so avoid applying repellent to the hands of children.
  • Whenever you use an insecticide or insect repellent, be sure to read and follow the manufacturer's DIRECTIONS FOR USE, as printed on the product.
  • For detailed information about using repellents, see the Insect Repellent Use and Safety questions.   

Frequently Asked Questions About Mosquito Spraying:

What are mosquito adulticides?

Adulticides are insecticides applied to kill adult mosquitoes. The most commonly used adulticides to control mosquitoes include: Permethrin, Malathion, Resmethrin, Pyrethrins, and Naled. Insecticides, such as permethrin, are used to control adult mosquitoes around homes and out-buildings.

What is adulticiding?

Adulticiding is the application of insecticides to control adult mosquitoes. It is an important part of an effective mosquito management program if it is based on mosquito surveillance information.

How does mosquito adulticiding work?

The idea behind mosquito adulticiding is to release the insecticide in as many very fine droplets as possible. Adult mosquitoes are killed when they come into contact with one of these droplets as they are flying. Very fine droplets are used because the more droplets there are and the longer the droplets stay in the air, the better the chances are that a droplet will come in contact with a mosquito.

Will adulticides be used for mosquito control in my neighborhood?                        

Mosquito adulticides are applied as a last resort when public health officials believe the potential health risks from West Nile virus or other mosquito-borne illness outweigh the potential risk from exposure to the insecticide. Factors that influence the decision to spray include: degree of threat to humans, infection rates in mosquitoes, species of mosquito and mosquito habitat.  The public is notified when this decision is made.  Only the minimum level of adulticide necessary to control mosquito activity is applied.

What is “backpack” spraying?

Hand-held and backpack sprayers are tools used to apply pesticides on limited sites. Appling pesticide to a target area by this equipment is called backpack spraying.     

What is fogging?

Fogging is the application of mosquito adulticides in the form of very fine droplets.  This method is used to target adult mosquitoes.  Adult mosquitoes are killed when they come into contact with one of these droplets as they are flying.

What are barrier treatments in adult mosquito control?

Longer-lasting adulticides may be applied to known adult resting areas to provide longer term control. Such treatments are referred to as barrier treatments.  Barrier treatments are intended to make a chemical barrier between a mosquito breeding site and an inhabited area. Typically, these are applied by homeowners or on a limited scale by public mosquito control programs, using handheld equipment to spray plants and other mosquito resting areas around the edges of their property. The insecticides used for barrier treatments last much longer in the environment than those applied by fogging.

Are adulticides any better at killing mosquitoes than pesticides that attack larval mosquitoes (larvicides)?

The use of mosquito larvicides generally is considered preferable to the use of adulticides for several reasons. (1) Use of mosquito larvicides prevents the appearance of the blood feeding adults. (2) Mosquito larvicides can provide up to a month of control, rather than the few hours provided by fogging with adulticides. (3) The commonly used mosquito larvicides are less toxic than the adulticides and are applied in such a way that there is much less human exposure. (4) Mosquito larvicides generally are applied to smaller areas than are adulticides.

If we use adulticides for mosquito control now, does that mean we do not need to use mosquito larvicides?

Effective mosquito control programs emphasize larval control and source reduction. Mosquito larvicides will continue to be used to minimize the need for adult control, along with source reduction (i.e., elimination of standing water of any size if possible)

Am I likely to be exposed to mosquito adulticides?

Mosquito adulticides are used only in certain high-risk areas and in the minimum amount necessary to achieve better mosquito control. Insecticides are short lived and most of the risk occurs during the application and for an hour or so afterwards. Precautions to minimize your exposure to mosquito adulticides include:

• Remain inside during the spraying.
• Keep children inside during spraying and for about one hour after spraying.
• Avoid eye contact with the spray if you are outside during spraying, and rinse your eyes with water or eye drops if they do come in contact with the spray.
• Wash skin surfaces that come into contact with the insecticide.
• Consult your doctor if you think your health was affected by the spraying.

What problems could I have if I am exposed to mosquito adulticides?

The known health threats associated with commonly used mosquito adulticides are considered to be less serious than those posed by West Nile virus and other mosquito borne illnesses. The Environmental Protection Agency has a website with toxicology information on the pesticides used to control mosquitoes, www.epa.gov/pesticides/factsheets/skeeters.htm.

Are mosquito adulticides available to the public for home use?

Yes, a number of insecticides available to the public are labeled for mosquito control. Be sure to read, understand and follow all label instructions and precautions.

What is Permethrin insecticide?

Permethrin insecticide is used for fogging and barrier spraying to control adult mosquitoes. According to the Environmental Protection Agency (EPA), “Pyrethroids [permethrin is a type of pyrethroid] can be used for public health mosquito control programs without posing unreasonable risks to human health when applied according to the label.  Pyrethroids are considered to pose slight risks of acute toxicity to humans, but at high doses, pyrethroids can affect the nervous system.”  (Source: http://www.epa.gov/pesticides/health/mosquitoes/pyrethroids4mosquitoes.htm)

For additional questions and answers please visit:

http://www.cdc.gov/ncidod/dvbid/westnile/q&a.htm