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Lake County Forest Preserves | Preservation, Restoration, Education and Recreation

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West Nile Virus faq


Questions & Answers

Q: What is your Mosquito Management Policy?

We follow a Mosquito Management Policy approved in 2003. The policy outlines how we control mosquitoes if they pose a significant health risk to preserve visitors or adjacent neighbors. We will not control nuisance mosquitoes that do not pose such a health risk. Instead, we will depend on natural ecosystem functions to keep mosquitoes in balance with the environment.

We provide information about the level of risk posed by WNV and what people can do to limit their exposure through public education, such as this website.

Our WNV Mosquito Management Technical Advisory Committee created the approved policy to guide future mosquito monitoring and management efforts in the preserves. This committee includes Federal, State and County public health, mosquito management, and conservation experts. Our policy also follows Centers for Disease Control recommendations.

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Q: How do you monitor and control mosquitoes?

We work with professional mosquito management consultants to identify sites where the types of mosquitoes capable of transmitting WNV may be breeding. We monitor mosquito populations at those sites, especially sites that receive high numbers of visitors or are located near areas with dense human populations.

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Q: What is larvicide, and how is it used to control mosquitoes?

Larvicide is an insecticide that is specifically targeted against the larval life stage of an insect. We apply larvicide to targeted areas where samples provided evidence of breeding Culex mosquitos. If applied, we use the most target-specific larvicide available. We currently use Bacillus sphaericus. This larvicide targets immature mosquitoes in breeding areas of standing water. Larvicide does not harm humans, birds or fish.

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Q: What is adulticide, and how is it used to control mosquitoes?

Adulticide is an insecticide that is specifically targeted against the mature adult life stage of an insect.Only in extreme circumstances do we consider spraying for adult mosquitoes due to questions about the effectiveness of spraying and the potential for ecological damage. Research on the effects of using adulticide is ongoing. This method is only used as a last resort and may be ineffective in a natural setting because the compound must come into contact with an insect to kill it. In natural areas, such as prairies or woodlands, mosquitoes often inhabit areas under leaves or in dense vegetation where they may escape contact. Ideally, adulticide is sprayed in open areas interspersed with roads or trails.

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Q: How can I protect myself from West Nile Virus?

Wear light-colored clothing with long sleeves, long pants and socks while outdoors for extended periods. In problem areas, spray clothing with repellents containing DEET or permethrin, avoid spraying these directly onto your skin. Some herbal repellents are effective; try different products to find one that works for you. Limit your time outdoors between dusk and dawn, which is peak mosquito time.

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Q: How can I reduce mosquito populations around my home?

Mosquitos require standing water to breed. Routinely empty water from your flowerpots, pet bowls, clogged rain gutters and other catch basins where mosquitoes will lay eggs. Frequently clean and refill birdbaths. Drill drainage holes in tires used in boat docks, landscaping or tire swings. 

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Q: How is West Nile Virus transmitted?

The main transmission of WNV involves certain types of mosquitoes, primarily Culex spp. andAedes spp.. Mosquitoes become infected with WNV when they feed on a bird carrying the virus in its blood. The virus circulates in a mosquito’s blood for a few days and the moves into the insect’s salivary glands, at which time the virus can be transmitted to another bird, human or other animal by bite. After a mosquito has injected WNV into a host, it can then replicate and may cause illness. However, even in areas where WNV is circulating, very few mosquitoes are infected with it. Unlike the common cold or flu, WNV is not transmitted through casual contact between people.

In its native range of Africa, West and Central Asia and the Middle East, there are occasional flare-ups of WNV-related illnesses. However, in most years there is not a widespread health concern. There is evidence indicating that people may develop immunity to the virus after exposure. Currently, WNV immunity and the potential for a vaccine are being researched.

Larvicide application

Larvicide is an insecticide that is specifically targeted against the larval life stage of an insect. We apply larvicide to reduce mosquito populations at targeted sites that are identified through our monitoring efforts. If applied, we use the most target-specific larvicide available. We currently use Bacillus sphaericus. This larvicide targets immature mosquitoes in breeding areas of standing water. Larvicide does not harm humans, birds or fish.

Adulticide application

Adulticide is an insecticide that is specifically targeted against the mature adult life stage of an insect.Only in extreme circumstances do we consider spraying for adult mosquitoes due to questions about the effectiveness of spraying and the potential for ecological damage. Research on the effects of using adulticide is ongoing. This method is only used as a last resort and may be ineffective in a natural setting because the compound must come into contact with an insect to kill it. In natural areas, such as prairies or woodlands, mosquitoes often inhabit areas under leaves or in dense vegetation where they may escape contact. Ideally, adulticide is sprayed in open areas interspersed with roads or trails.

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Q: What are the symptoms of WNV?

Most people with WNV do not develop symptoms. Some people may become ill three to 15 days after being bitten by an infected mosquito.

Mild illness, called West Nile Fever, may include headache, body ache, fever, and sometimes skin rash and swollen glands. Less than 1% of people who are bitten and become ill with West Nile Fever have it intensify into a severe illness known as West Nile Encephalitis. Encephalitis is an inflammation of the brain that may be marked by headache, high fever, stiff neck, stupor, disorientation, coma, tremors, convulsions, muscle weakness and paralysis. A small number of cases have been fatal.

People are only at risk of becoming infected with WNV when they are in areas where the virus has been circulating among mosquito populations for a long period of time. Risk to humans is most prevalent in Illinois and other northern states during August and September. Those at greater risk of the milder illness, West Nile Fever, and the more serious West Nile Encephalitis include people 50 years of age and older, and those with existing respiratory or immune system problems.

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