Utah Pests News Summer 2007

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Reduce Your Risk of West Nile Virus in 2007



Female mosquito laying eggs in stagnant water.

West Nile Virus (WNV) is a relatively new disease in the United States, but has made a significant impact to Utahns in a short amount of time. First detected in New York in 1999, WNV quickly spread throughout the United States, Canada, and Mexico in less than four years. Horses and humans have been particularly affected by WNV. In 2006, more than 150 people were diagnosed with moderate or severe symptoms in Utah, and five people died as a result of secondary complications to WNV.

Although most people (80%) infected with WNV will never display any symptoms, everybody should be aware of how to reduce the risk of an infection. In general, female mosquitoes like to lay eggs in stagnant water; reducing standing water will help reduce potential sources for mosquito production.

Here are ways to reduce your risk.

    • Eliminate small pools of water (e.g., wheelbarrows, tires).
    • Keep containers clean and dry when not in use (e.g., watering cans).
    • Allow drainage in outdoor containers so standing water is reduced (e.g., garbage cans).
    • Keep water fresh and properly chlorinated (e.g., ornamental ponds, pet bowls, pools).

About 20% of people infected with WNV display mild or moderate symptoms similar to the flu. To date, there are no vaccines to prevent WNV or any medicines to cure an infected person. Less than 1% of humans infected with WNV will experience severe symptoms that require hospitalization. People over the age of 50 or immuno-compromised people are a higher risk of developing serious complications or fatalities. Severe symptoms include extreme headache, tremors, disorientation, coma, paralysis, encephalitis, and meningitis. If you experience moderate or severe symptoms, consult a physician. Screening for WNV antibodies is the only way to confirm an infection.

According to Sammie Dickson, Ph.D. (Salt Lake City Mosquito Abatement District), Culex tarsalis and C. pipiens are the two most common mosquito species responsible for transmitting WNV in Utah. Culex tarsalis is the most abundant and virulent mosquito, meaning a female mosquito is very likely to transmit the virus while taking a blood meal. Culex tarsalis prefers to feed on birds and small mammals in rural areas, but will move into residential neighborhoods too; this species is the most common vector to humans and horses in Utah. Culex pipiens is the second most common mosquito to vector WNV in Utah. Although not as abundant or virulent as C. tarsalis, it is more widespread in urbanized areas (towns with >20,000 people). Because C. pipiens is more commonly found where people live, this mosquito is likely increasing the transmission rates to humans by amplifying WNV in birds and mammals.

There are several things people can do to further reduce the risk of getting WNV. Keep mosquitoes from coming into the home by repairing screens and sealing windows. Wear long sleeved shirts and pants when outside in areas with biting mosquitoes. Avoid being outdoors when mosquitoes are especially active; Culex mosquitoes prefer to take blood meals between dusk and dawn. Mosquito repellent may be the best way to prevent bites and subsequent WNV infections. Depending on your level of outdoor activity, there are many different kinds of repellents available. Choose a repellent you and your family will use consistently. Products approved by the EPA (Environmental Protection Agency) include:

    • DEET is the most common mosquito repellent product because it is effective and available in several concentrations. DEET can be applied to the skin, however should not be sprayed directly onto the face.
    • Picaridin is a relatively new product available in Utah. It provides an alternative to people who are sensitive to DEET products. Picaridin is nearly odorless and can be applied directly to the skin.
    • Permethrin is a highly effective repellent and is generally used for long periods of outdoor activity or in more remote locations. Permethrin should not be applied directly to the skin, but can be used on clothing, shoes, and camping equipment.

For more information, see the Utah Pests Fact Sheet, West Nile virus in Utah. Or visit the Utah Department of Health for current WNV details (http://www.health.utah.gov or 801.538.6191). To learn more about horse vaccinations, contact the USU Vet Extension (http://extension.usu.edu/equine or 435.797.1880). If you want to report dead birds, call 801.476.2470.

-Erin Hodgson, Extension Entomologist