Mosquito-borne encephalitis season returns

Staff Report

The warmer weather of spring and spring rain means Winnebago County residents should start noticing increased mosquito activity. It is still too early to know what amount of West Nile virus (WNV) or St. Louis encephalitis (SLE) activity we will have in our community this season.

Above-normal temperatures appear to increase the rate of Culex mosquito production, mosquito flight activity and virus replication, thereby increasing the proportion of birds and mosquitoes infected with WNV or SLE and the risk of disease to humans.

West Nile virus and St. Louis encephalitis are both transmitted to humans from the bite of a mosquito that has picked up the virus by feeding on an infected bird. In the summer of 2010, Winnebago County Health Department received 100 calls from the general public with questions about West Nile virus and dead bird reports. Those calls resulted in 10 birds being sent to the state lab, with eight being confirmed as positive with infection by West Nile virus.

Based on nationwide experience in Illinois over the previous nine years of WNV presence in the United States, the peak period for WNV transmission, particularly to humans, has been from mid-July through the middle of October. It is important to keep in mind again that this is influenced by many environmental factors that affect the viral amplification cycle (e.g., weather, host and vector densities, immune status and other characteristics).

“Once again, the Winnebago County Health Department has opened a phone line for residents to report the location and number of dead birds,” said Center for Environmental Health Improvement Director Larry Swacina. “The list of reportable birds for WNV surveillance includes: crows, blue jays, grackles, starlings, sparrows, finches, robins, cardinals, flycatchers, swallows, catbirds, mockingbirds, warblers, wrens, hawks, owls and gulls. The report line number to call is (815) 720-4245. After calling in a report of a dead bird, you can dispose of the bird yourself, or leave it where it lay, if not picked up for testing within 24 hours of your call.”

When calling the hotline to report dead birds, leave the address, ZIP code, town, and type and number of dead birds found. The Illinois Department of Public Health has limited the number of dead birds that can be submitted for WNV testing in 2011 by Winnebago and other counties.

“Remember, dead birds cannot spread West Nile virus, but it is advised to avoid barehanded contact with dead birds and other animals since they carry a variety of germs. Use a shovel, gloves or double plastic bags to place the carcass in a garbage bag or can,” Swacina said.

The Health Department has also opened a West Nile Virus Information line for residents who have questions or wish to speak to a health professional. That number is (815) 720-4240.

The best protection against mosquito-borne encephalitis is to limit activities at dawn and dusk, when mosquitoes that could carry the virus are most active. Protective clothing will ideally include lightweight, loose-fitting, long-sleeved shirts, pants and socks. It’s best to always apply a repellent containing DEET (25 percent for adults, 10 percent for children, and not recommended for infants) when going outdoors. CDC has added additional products containing picaridin and lemon of eucalyptus. Both ingredients have also proven effective as mosquito repellents.

Most people infected with West Nile virus or St. Louis encephalitis have no signs or symptoms of illness. Some individuals may become ill, usually three to 15 days after having been bitten by an infected mosquito. The virus may occasionally cause serious complications. In some individuals, particularly the elderly, the virus can cause muscle weakness, inflammation of the brain (encephalitis), stiff neck, stupor, disorientation, tremors, convulsions, paralysis, coma or death. It should be noted that the odds of being bitten by an infected mosquito and developing serious or life-threatening symptoms are minimal. Nevertheless, taking all recommended precautions (below) is encouraged, because of the potential seriousness of becoming infected by West Nile virus or St. Louis encephalitis.

Precautions to prevent mosquito-borne encephalitis

– Alert health authorities to potential mosquito breeding sites in your area.

– Avoid outdoor activities in the early morning and at dusk. Whenever outdoors between dusk and dawn, wear shoes and socks, long pants and a long-sleeved shirt. Loose-fitting, light-colored clothing is best.

– Apply insect repellent to exposed skin. An effective repellent will contain 25 to 35 percent of the active ingredient DEET or picaridin or lemon of eucalyptus. Spray the repellent not only on exposed skin, but also on clothing. Consult a physician before using repellents on very young children.

– Drain standing water in your yard at least once a week. Pour water from mosquito breeding sites, such as flower pots, pet bowls, clogged rain gutters, swimming pool covers, boats, discarded tires, buckets, barrels, cans or similar items in which mosquitoes can lay eggs. For permanent standing pools of water, mosquito larvicide can be used. The larvicide can be purchased from many retail stores selling garden supplies. Follow the manufacturer’s recommendations for use.

–  Check screens on porches and patios for tears and other openings.

Visit the following websites for more info:

Illinois Department of Public Health at;

Center for Disease Control at; or

Winnebago County Health Department at

From the May 25-31, 2011 issue

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