West Nile mosquitoes are back in area

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Dan Jonas (left) of Western Springs and Pat Thor Larsen of Riverside check for mosquito larvae in a pond. Desplaines Valley Mosquito Abatement District sprays or ads chemicals to kill mosquito larvae in standing water. | Rob Hart~Sun-Times Media

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Updated: October 31, 2011 10:42AM

The DuPage County Health Department announced Friday that the first positive test for West Nile Virus in 2011 came from mosquitoes taken from trap in Lemont.

The mosquitoes that tested positive were collected July 6 and tested the following day.

The wet and cool spring delayed the development of the mosquitoes that spread West Nile Virus, according to information from the DuPage County Health Department. However, the recent hotter temperatures are more conducive to the spread of West Nile Virus.

Stagnant water is considerably more conducive for species of mosquitoes that carry West Nile Virus, said David Hass, public information officer for the DuPage County Health Department.

“When we have storms that stir up stagnant water, those mosquitoes don’t like that,” Hass said. “When we continue to have a lot of storms come through the area it does result in more of the nuisance mosquitoes that will bite you, but don’t carry the virus.”

Hass said it’s very likely additional West Nile mosquitoes will be found elsewhere in the region.

“We continue to check and get reports,” he said. “We haven’t had any other reports, yet, but it’s coming.”

DuPage County residents who want to track West Nile virus in their communities may do so online at www.dupagehealth.org/wnv-map. An online map of mosquito traps throughout the county will be updated as mosquitoes test positive for West Nile Virus. Cook County communities also are experiencing problems.

“We’ve been quite busy with all those spring rains and a bumper crop of nuisance mosquitoes. They were bad,” said biologist Paul Geery, assistant manager of the Desplaines Valley Mosquito Abatement District in western Cook County.

“We kept getting rain after rain after rain, with brood after brood after brood,” Geery recalled. “But things have dried up quite a bit and they’re dying off from old age. There have been no new nuisance mosquitoes.

“It’s definitely better than a week ago and better than two weeks ago.”

Although the nuisance mosquitoes are annoying, biologists and health officials are far more concerned with the appearance of the Culex pipiens, which carries the West Nile virus and can prove deadly for a few people with certain health conditions.

The virus is spread by mosquitoes, which feed on infected birds and later, other animals. Also known as house mosquitoes, the insects prefer hot, dry conditions along with stale standing water for breeding.

“We did have a fairly cool spring and that helped keep down the virus-carrying species,” Geery said. “But about this time of year, we’re holding our breath. If it stays hot and dry, we could see the population go up very quickly.”

Crews from the abatement district, which includes towns in Lyons and Proviso townships in a 77-square-mile region, have counted fewer locales with house mosquitoes than a year ago.

No mosquitoes have tested positive with the virus in the district so far, but cases were found July 5 in Evergreen Park and Oswego in Kendall County. The virus was detected earlier in birds

To combat the virus, which peaked in the Chicago area in 2002, many control experts favor applying larvicides to breeding areas before hatching mosquitoes become airborne, Geery said. Fogging adult infected mosquitoes with a spray is a last resort.

“We’re treating all the sites we now of. They can breed in standing water from ponds, to a small tin can,” he said. “A lot of gutters are plugged. We can’t track every gutter, wheelbarrow or bucket not turned over.

“That species has plenty of places to lay eggs. We do encourage folks to look around their yard and check for standing water.”

The recession and rise in foreclosures have boosted the number of breeding spots through swimming pools, homes and yards not being maintained.

“Those scattered sources can be problematic. We have a fairly big list of in-ground pools that sit there and crank out millions of mosquitoes, and we’re treating them on a regular basis,” Geery said. “Our goal is to encourage people if they’re not using their swimming pool to fill it in or take it down.”

The DuPage County Health Department is collecting freshly-dead birds for testing. To be used for testing, birds must not show any signs of decay or trauma, and the department must be able to pick them up in time to be shipped to the state laboratory by the close of business on Thursdays. DuPage County residents can report a dead bird by calling (630) 682-7400.

The following precautions offer the best way to prevent West Nile or any other mosquito-borne illness:

Avoid being outdoors when mosquitoes are most active, especially between dusk and dawn

When outdoors, wear shoes and socks, long pants and a long-sleeved shirt, and apply insect repellent that includes DEET, picaridin, oil of lemon eucalyptus or IR 3535 according to label instructions. Consult a physician before using repellents on infants

Make sure doors and windows have tight-fitting screens. Repair or replace screens that have tears or other openings. Try to keep doors and windows shut, especially at night

Eliminate all sources of standing water that can support mosquito breeding, including water in bird baths, ponds, flowerpots, wading pools, old tires and any other receptacles

In communities where there are organized mosquito control programs, contact your municipal government to report areas of stagnant water in roadside ditches, flooded yards and similar locations that may produce mosquitoes.