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News from Wyoming Department of Health

Take Steps to Prevent West Nile Virus Infection


As Wyoming’s summer season nears, residents should take action to protect themselves from West Nile virus according to a Wyoming Department of Health representative.

“Preventing mosquito breeding and avoiding mosquito bites are common-sense steps everyone should take,” said Emily Thorp, surveillance epidemiologist with the Infectious Disease Epidemiology Program at the Wyoming Department of Health.

West Nile virus (WNV) can cause potentially serious illness in humans. Mosquitoes spread the virus by feeding on infected birds and then biting people, other birds and animals. Wyoming has seen human cases of WNV reported as early as May and as late as October with late summer and early fall as the typical peak times.  

In Wyoming last year there were 12 human WNV cases with 1 death reported. There were 10 human cases with no deaths in 2008; 185 human cases with 2 deaths in 2007; 65 human cases with 2 deaths in 2006; 12 human cases with 2 deaths in 2005; 10 human cases with no deaths in 2004; and 393 human cases with 9 deaths in 2003.

“No one should think the low case numbers we’ve seen in recent years means this disease is no longer a threat,” Thorp said. “West Nile virus activity is difficult to predict.”

Thorp said factors affecting WNV transmission include effectiveness and timing of mosquito spraying, bird migration patterns, weather (both last year and this year), virus genotype, amount and location of standing water or irrigation on or near a person’s property, and awareness and use of personal prevention methods.

“So the best and easiest thing a person can do to avoid infection with West Nile virus is to abide by the 5’ds of prevention,” Thorp said. The “5 D’s” of prevention are:

1) DAWN and 2) DUSK - Most mosquito species prefer to feed at dawn or dusk, so avoid spending time outside during these times.
3) DRESS - Wear shoes, socks, long pants and a long-sleeved shirt when spending time outdoors or when mosquitoes are most active. Clothing should be light-colored and made of tightly woven materials to keep mosquitoes away from the skin.
4) DRAIN - Mosquitos breed in shallow, stagnant water. Reduce the amount of standing water by draining and/or removing it.
5) DEET - Use an insect repellent containing DEET (N, N-diethyl-m-toluamide). When using DEET, be sure to read and follow the instructions on the product’s label. Other insect repellents such as Picaridin (KBR 3023) or oil of lemon eucalyptus can also be effective.

Property owners should also act to reduce mosquito breeding grounds:

• Use smart landscaping to eliminate standing water that collects.
• Repair failed septic tanks.
• Dispose of containers that collect water such as tin cans, ceramic pots, or plastic containers.
• Remove or discard old tires.
• If you cannot dispose of old tires, drill holes in them to allow water to drain.
• For containers such as bird baths or troughs, replace all of the water at least once a week.
• Repair leaky water pipes and outdoor faucets.
• Ensure that roof gutters drain properly.
• Turn over plastic wading pools and wheelbarrows when not in use.
• Cover trash containers to keep water out.
• Aerate ornamental ponds or stock them with predatory fish.
• Clean and chlorinate outdoor swimming pools even when not in use.
• Keep drains, ditches, and culverts free of grass clippings, weeds, and trash so water will drain properly.
• Remove vegetation and debris from the edge of ornamental ponds.

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