For Immediate Release
Contact: Tim Hadac
Phone: (312) 747-9805
Email: hadac_tim (at) cdph.org
Thurs., Aug.18, 2005

Fewer Mosquitoes Means Less Risk of West Nile Virus

City officials today said they will again spray insecticide on the North and South Sides to hold down the mosquito population and reduce the risk of human illness caused by the West Nile Virus.

"In a city of 228 square miles, we can't eliminate every mosquito or prevent every mosquito bite," stated Chicago Dept. of Public Health (CDPH) Medical Entomologist John-Paul Mutebi, Ph.D., "but we can continue to take proactive steps to reduce the mosquito population and therefore reduce people's risk of getting infected with the West Nile Virus. That is what we intend to do."

The spraying will be conducted on Sunday and Monday nights (Aug.21 and 22) by licensed technicians from Clarke Mosquito Control. The Clarke trucks will again be guided through streets and alleys by staff from the Chicago Department of Streets and Sanitation. Some of the areas to be sprayed are mostly similar to those that were sprayed on the evenings of July 31 and Aug.1, 7 and 8. A significant number of neighborhoods have been added on the Southeast and Southwest Sides, based on new data. (See attached spraying schedule and map.)

An identical two-night spraying effort is planned for Sunday, Aug.28 and Monday, Aug.29.

The decision to spray insecticide again was made after an analysis of CDPH mosquito traps showed that recent spraying reduced the mosquito population in the targeted areas by an estimated 50 percent. However, surveillance data also show that about 28 percent of all mosquitoes in CDPH traps are infected with the West Nile Virus—an indicator that the risk to people remains high.

"While our first round of spraying dealt a powerful blow to the mosquitoes, it is clear—both from our own data and from the fact that West Nile has spread so rapidly in the suburbs—that we need to spray again to prevent the mosquito population from resurging," added CDPH Communicable Disease Program Medical Director Susan Gerber, M.D. "As we know from the many cases of human illness we have seen since 2002, the West Nile Virus is dangerous and potentially deadly. We can and will take all reasonable steps necessary to protect the public health."

The Clarke trucks will dispense an ultra-low-volume spray. The spray's active ingredient is Anvil, an insecticide approved for use by the U.S. Environmental Protection Agency. Just one tablespoon of Anvil is used per acre of land covered. While Anvil is approved for use in residential settings and is used regularly across the nation, CDPH officials note that it is, nonetheless, a pesticide and that all Chicagoans are advised to limit their exposure to it—just as a person would limit exposure to a pesticide sprayed out of an aerosol can. Common-sense ways to limit exposure include staying indoors and closing windows while spraying is underway; setting air conditioning units to re-circulate; and bringing in children's toys. While Anvil is effective against mosquitoes in flight, it breaks down very quickly in sunlight and water.

CDPH officials also announced that three new human cases of disease related to the West Nile Virus have been confirmed in the city, prompting a reminder for everyone to take simple steps to avoid mosquito bites.

The city's fifth case of 2005 is a 60-year-old woman who lives in the Dunning neighborhood of the Northwest Side. She was admitted to a hospital on Aug.7 with West Nile Fever and discharged on Aug.12.

The sixth case of the year is a 54-year-old woman from the Norwood Park neighborhood on the Northwest Side.

She became ill on Aug.7 and remains hospitalized with encephalitis.

The seventh case is a 51-year-old man from the Northwest Side's Dunning neighborhood, who was hospitalized with meningitis on Aug.9 and discharged on Aug.16.

So far this year, human cases of West Nile-related illness have been confirmed in the O'Hare, Dunning and Norwood Park neighborhoods on the Northwest Side, New City on the South Side, and Clearing and Beverly on the Southwest Side.

Infected mosquitoes and/or birds have been found in the O'Hare, Dunning, Forest Glen, North Park, West Ridge, Norwood Park, South Deering, Edison Park, Edgewater and Portage Park neighborhoods of the North and Northwest Sides; and in the Beverly, Morgan Park, Mount Greenwood, Clearing, Garfield Ridge, Chicago Lawn, West Pullman, Roseland, South Shore, Eastside and Hegewisch neighborhoods of the South, Southwest and Southeast Sides.

More About West Nile

The Northern House mosquito, Culex pipiens, is the primary carrier of West Nile virus. This mosquito species thrives in water with high organic content, such as that found in catch basins (storm sewers). Consequently, a hot, dry summer (like the current one) increases the risk of West Nile virus infection, exactly the opposite of what many people believe. In contrast, the swarms of "floodwater" mosquitoes that appear after heavy rains may be a nuisance, but they rarely are infected with West Nile virus.

In 2002 some 4,156 human cases (284 of them fatal) of West Nile-related illness were reported nationally. In Illinois there were 884 reported cases and 67 deaths. In Chicago there were 225 reported cases and 22 deaths. Human case numbers fell off dramatically in 2003, with just four reported illnesses and no fatalities in Chicago. Last year there were six cases (one fatal) in the city. Thus far in 2005, there have been four reported human cases of West Nile-related illness in the state. Human cases have already been reported in 18 states in 2005.

Preventing West Nile Infection

CDPH officials ask all Chicagoans to take precautions to protect themselves and their families from mosquito bites. Especially important is the use of insect repellant containing DEET (N, N-diethyl-meta-toluamide), Picaridin (KBR 3023) or Oil of Lemon eucalyptus (PMD).

An example of a product containing Picaridin is Cutter Advanced Insect Repellent, available at stores across the city.

In addition to using insect repellant to avoid bites, CDPH officials advise:

Consider limiting outdoor activity after dark (dusk to dawn), which is when Northern House Mosquito is most active.
When outside between dusk and dawn, wear loose-fitting, light-colored clothing that includes long pants, long-sleeved shirts, socks and shoes.
Check to see that all screen on doors and windows are tight-fitting and free of holes and tears.
Encourage neighbors to exercise precautions.
To limit mosquito breeding opportunities, CDPH officials recommend:

draining and replacing water in birdbaths and children's backyard wading pools every four to five days;
properly disposing of old tires, jars, cans, pans, bottles, buckets and other unwanted containers that can hold standing water;
making sure that rain gutters, downspouts, swimming pools and pool covers are free of standing water;
keeping grass and weeds cut short to eliminate hiding places for adult mosquitoes;
West Nile Virus infection can cause a relatively mild illness called West Nile Fever, characterized by fever, muscle aches, rash and headache. More severe West Nile illness is less common, but can include meningitis (inflammation of the membrane surrounding the brain) and encephalitis (inflammation and swelling of the brain itself). People of all ages are susceptible to West Nile infection, but people over age 50 are at greater risk of developing severe illness.

The City of Chicago's aggressive campaign against the Northern House Mosquito is led on a year-round basis by Mayor Richard M. Daley's Task Force on West Nile Virus, which meets regularly to assess past efforts and improve methods of disease surveillance, mosquito control and public education.

To date, the Task Force has led an effort that has seen hundreds of thousands of catch basins treated with larvicide that significantly limits mosquito breeding opportunities. Other city efforts have included identifying and eliminating sources of standing water, and the printing and dissemination of thousands of informational brochures to sites across the city.

West Nile Virus informational brochures may be obtained by visiting any Chicago Public Library branch or by calling 311.

For prevention tips and weekly updates on West Nile Virus activity in Chicago, visit our web site at cityofchicago.org/health.

For an expert national perspective on West Nile Virus, visit the official web site of the CDC.

Mosquito Spraying Schedule and Map

First night (dusk Sunday, Aug. 21 – dawn Mon., Aug. 22):

South/Southwest Side (two areas):

roughly bounded by 87st St. on the north, city limits on the south, Stony Island on the east, city limits on the west;
roughly bounded by 47st St. on the north, 87st St. on the south, Ashland on the east and city limits on the west.
Southeast Side (two areas):

roughly bounded by 100st St. on the north, 118st St. on the south, Calumet River on the west and Avenue F on the east.
roughly bounded by 125st St. on the north, 136st St. on the south, Avenue K on the east and Saginaw on the west.
Second night (dusk Mon., Aug. 22 – dawn Tue., Aug. 23):

North/Northwest Side
area roughly bounded by city limits on the north, Belmont on the south, the eastern edge of O'Hare on the west, and Western Ave. on the east.

Current plans call for this two-night spraying schedule to be repeated on Sunday, August 28 and Monday, August 29.