West Nile Virus

Avoiding Mosquito Bites Still the Best Policy

West Nile Virus will continue to be a problem on the Front Range of Colorado for many years to come. July through September are peak times for the disease, but throughout the year caution is still the best policy. Everyone is encouraged to avoid mosquito bites by wearing insect repellent when outdoors, and by eliminating standing water where mosquitoes can breed.

Colorado Mosquito Control continues to handle the mosquito population for the City of Thornton. They use larvaecide to kill mosquitoes where they breed, and also respond to residents with mosquito problems. These problems can either be large numbers of biting mosquitoes, or mosquito breeding sites such as storm sewers, ditches and abandoned properties with standing water. To report either of these two problems, or to ask that spraying not be done near your home, call the Mosquito Hot Line at 303-558-8730.

Using Pesticides and Repellents

A wide variety of insect repellent products are available. The Center for Disease Control (CDC) recommends the use of products containing active ingredients which have been registered with the U.S. Environmental Protection Agency (EPA) for use as repellents applied to skin and clothing. EPA registration of repellent active ingredients indicates the materials have been reviewed and approved for efficacy and human safety when applied according to the instructions on the label.

Of the active ingredients registered with the EPA, two have demonstrated a higher degree of efficacy. Products containing these active ingredients typically provide longer-lasting protection than others...

• DEET (N,N-diethyl-m-toluamide)
• Picaridin (KBR 3023)

Oil of lemon eucalyptus [p-menthane 3,8-diol (PMD)], a plant based repellent, is also registered with EPA. In two recent scientific publications, when oil of lemon eucalyptus was tested against mosquitoes found in the US it provided protection similar to repellents with low concentrations of DEET. In addition, certain products which contain permethrin are recommended for use on clothing, shoes, bed nets, and camping gear, and are registered with EPA for this use. Permethrin is highly effective as an insecticide and as a repellent. Permethrin-treated clothing repels and kills ticks, mosquitoes, and other arthropods and retains this effect after repeated laundering. The permethrin insecticide should be reapplied following the label instructions. Some commercial products are available pretreated with permethrin.

Length of protection from mosquito bites varies with the amount of active ingredient, ambient temperature, amount of physical activity/perspiration, any water exposure, abrasive removal, and other factors. For long duration protection use a long lasting (micro-encapsulated) formula and re-apply as necessary, according to label instructions.

The EPA recommends that the following precautions be followed when using insect repellents...

• Apply repellents only to exposed skin and/or clothing (as directed on the product label.) Do not use repellents under clothing.
• Never use repellents over cuts, wounds or irritated skin.
• Do not apply to eyes or mouth, and apply sparingly around ears. When using sprays, do not spray directly on face—spray on hands first and then apply to face.
• Do not allow children to handle the product. When using on children, apply to your own hands first and then put it on the child. You may not want to apply to children’s hands.
• Use just enough repellent to cover exposed skin and/or clothing. Heavy application and saturation are generally unnecessary for effectiveness. If biting insects do not respond to a thin film of repellent, then apply a bit more.
• After returning indoors, wash treated skin with soap and water or bathe. This is particularly important when repellents are used repeatedly in a day or on consecutive days. Also, wash treated clothing before wearing it again. (This precaution may vary with different repellents—check the product label.)
• If you or your child get a rash or other bad reaction from an insect repellent, stop using the repellent, wash the repellent off with mild soap and water, and call a local poison control center for further guidance. If you go to a doctor because of the repellent, take the repellent with you to show the doctor.

Note that the label for products containing oil of lemon eucalyptus specifies that they should not to be used on children under the age of three years. Other than those listed above, EPA does not recommend any additional precautions for using registered repellents on pregnant or lactating women, or on children. For additional information regarding the use of repellent on children, follow this link to the CDC’s FAQ on Repellent Use.