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West Nile Virus Facts and Insect Bite Prevention

Quick Tips #258

West Nile Virus first made headlines after a number of cases were reported and identified in the United States. However, this virus is not exactly new. In fact, West Nile Virus was first identified in 1937 in the West Nile District of Uganda, and the first appearance in North America was in 1999.

How is West Nile Virus Spread?

Infected mosquitoes spread West Nile Virus. Mosquitoes most commonly pick up the disease from infected birds, and go on to infect other animals while feeding on their blood. In a mosquito, the virus is found in the salivary glands which mosquitoes use to anesthetize the skin of the animal on which they are feeding.

West Nile Virus in Humans

In the bloodstream of humans, the virus multiplies and crosses the blood/brain barrier. When this happens, the virus can cause West Nile encephalitis, a serious condition resulting in the inflammation of brain tissue. However, it is important to note that most people who become infected have either no symptoms, or only mild symptoms. Also, if a person does contract the virus, a natural immunity is developed that is assumed to last all their life. Note: the virus cannot be spread by human-to-human contact.

Insect Bite Prevention

While there is currently no vaccine for West Nile Virus, the Center for Disease Control has the following tips for reducing the risk of exposure. These include:

  • Stay indoors at dawn, dusk, and in the early evening
  • Wear long-sleeved shirts and long pants when outdoors
  • Spray clothing with repellents containing permethrin or DEET since mosquitoes may bite through thin fabric
  • Apply insect repellent containing 35% DEET to exposed skin (other effective mosquito repellents, as reported by the CDC in April 2005, are picaridin and oil of lemon eucalyptus)
  • Always read and follow manufacturer's directions when using repellents, and avoid applying to the hands of children
  • Install or repair window and door screens so that mosquitoes cannot get indoors
  • Vitamin B and "ultrasonic" devices are not effective in preventing mosquito bites

An unusual number of dead birds in an area may indicate the presence of West Nile Virus. While there are over 110 species of birds known to have been infected, the virus tends to be somewhat more lethal to crows and jays. State and local health departments are responsible for investigating reports of dead birds.

For more information on West Nile Virus, go to the Centers for Disease Control and Prevention.

Find a listing of State and Local Government Sites here.

DEET insect repellent fact sheet.

Updated Information regarding Insect Repellents including DEET alternatives.

Use Clothing, Repellents to Fight Off Bugs

Warmer temperatures are a sure sign that summer is on the way. And with the warmer temperatures come those pesky, nuisance insects to ruin your outdoor activities. A single acre of land can easily accommodate more than 400 million insects that can sting, bite, chew or just generally annoy us enough to want to stay indoors.

Insects such as hornets, bees and fire ants use stingers, which penetrate the skin and inject venom. Bites from mosquitoes and black flies initially cause itching, but it's the insects' saliva that's the main irritant. The saliva is highly acidic and can create swelling, welts and severe itching. Chiggers are chewers who tear small pieces of skin and secrete a liquid that dissolves skin cells. A close encounter with chiggers will leave you with one of the most itchy and painful of all insect wounds.

There are two options to fight off these insects. The first approach is to dress in loose pants and long-sleeved shirts. Mosquito netting is also a good idea for covering the face and neck. This full-body covering keeps insects away from the skin and prevents bites or stings.

A second option is to use insect repellent. The most commonly used repellents generally contain DEET (N, N-diethyl-m-toluamide), which was developed in 1946 by the U.S. military and made available to the public in 1957. Other repellents such as picaridin, also known as KBR 3023, and oil of lemon eucalyptus have been recently found to be effective alternatives to DEET for mosquito protection.

Although DEET works well as a repellent, it does have some shortcomings. In 1961, the New England Journal of Medicine reported a study on the effects of continuous exposure to DEET. The study indicated that DEET penetrated the skin and entered the bloodstream easily, and should therefore be used with caution. It found that some children generously treated with DEET for several weeks experienced seizures, convulsions and developed toxic encephalopathy. The study also reported that adults experienced confusion, irritability, insomnia and other neurological problems when exposed to high levels of DEET.

Health Effects

After completing a comprehensive reassessment of DEET, the Environmental Protection Agency (EPA) concluded that as long as users follow label directions and take proper precautions, insect repellents containing DEET do not present a health concern.

Rashes, blisters, skin and mucous membrane irritation, and numb or burning lips have occurred among people who applied products containing a high concentration (50 or 75 percent) of DEET and among those excessively exposed. Toxic encephalopathy and seizures have been associated with use in children. Subtle insomnia, mood disturbances and impaired cognitive function in adults has been associated with excessive application.

Suggestions for DEET Use

To prevent adverse reactions, it is recommended that DEET-based products be applied sparingly or over clothing rather than directly on the skin. Another option is using products that have low concentrations of DEET.

Other suggestions for DEET based repellent use include the following:

  • Read and follow all directions and precautions on the product label
  • Do not apply over cuts, wounds or irritated skin
  • Do not apply to hands or near eyes and mouth of young children
  • Do not allow young children to apply the product
  • Use just enough repellent to cover exposed skin and/or clothing
  • Do not use under clothing
  • Avoid over-application
  • After returning indoors, wash treated skin with soap and water
  • Wash treated clothing before wearing again
  • Do not spray aerosol or pump spray products in enclosed areas
  • To apply aerosol or pump spray products to face, spray on hands first and then rub on face
  • Do not spray directly onto face

The fact is, even with its shortfalls, an estimated 200 million people use DEET-based products and adverse reactions are extremely rare.

DEET Free Options

Two alternatives to DEET based repellents were announced by the CDC in an April 28th, 2005 press release. While the CDC still states that DEET is highly effective it does recommend products that contain either piraridin or oil of lemon eucalyptus as effective mosquito repellent options.

The release indicates that picaridin has been used for years in Europe, Australia, Latin America and Asia and evidence indicates that it works very well, often comparable with DEET products of similar concentration.

According to the CDC, oil of lemon eucalyptus (also know as p-menthane 3,8-diol or PMD) is, a plant-based mosquito repellent that provided protection time similar to low concentration DEET products in two recent studies.

A little planning and a few precautions can make a big difference when working, or playing outside. If you dress appropriately and have the right insect repellents on hand, your time spent outdoors can be safer and considerably more comfortable.



(Rev. 3/2014)

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Please Note:
The information contained in this publication is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This publication is not a substitute for review of the current applicable government regulations and standards specific to your location and business activity, and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.

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