Weather Updates

West Nile virus rarely carried by floodwater mosquitoes



storyidforme: 12491428
tmspicid: 4310238
fileheaderid: 2216217

Updated: September 29, 2011 12:50AM

SPRINGFIELD — Spring rains could make conditions ripe for mosquitoes in the coming days.

The Illinois Department of Public Health says people should be aware of the difference types of mosquitoes and which ones are most likely to carry West Nile virus.

Floodwater mosquitoes (Aedes vexans and other species) typically appear about two weeks after heavy rains and flooding, according to a press release from the health department.

While floodwater mosquitoes can be a nuisance, they are rarely infected with West Nile virus, or WNV.

However, as floodwaters recede into ditches, catch basins or other areas where water sits stagnant, house mosquitoes (Culex pipiens) typically will start to appear. It is house mosquitoes — when found in areas that have seen WNV in recent years — that are often infected with the virus, the health department noted.

“With the floodwaters and increasing temperatures, we’re going to start seeing increased mosquito activity,” Department of Public Health Director Dr. Damon T. Arnold said. “It is important to protect yourself against mosquito bites by wearing insect repellent and taking other precautions.”

Last year, 30 of the state’s 102 counties were found to have a West Nile-positive bird, mosquito, horse or human case. The first positive bird was collected on May 8, 2010, in Carroll County; and the first positive mosquito batches were collected on June 8, 2010, in Tazewell County. A total of 61 human cases of West Nile disease were reported in Illinois last year, the first reported on Aug. 31.

There have been no confirmed cases of West Nile virus so far this year.

West Nile virus is transmitted through the bite of a mosquito that has picked up the virus by feeding on an infected bird. Most people with the virus have no clinical symptoms of illness, but some may become ill three to 15 days after the bite of an infected mosquito. The first human case in Illinois is not usually reported until July or later, according to the health department.

Symptoms of illness

Only about two people in 10 who are bitten by an infected mosquito will experience any illness. Illness from West Nile usually is mild and includes fever, headache and body aches; but serious illness, such as encephalitis and meningitis, and death are possible, health officials said.

Persons older than 50 years of age have the highest risk of severe disease.

The best way to prevent West Nile disease or any other mosquito-borne illness is to reduce the number of mosquitoes around one’s home and to take personal precautions to avoid mosquito bites. Precautions include:

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

When outdoors, wear shoes and socks, long pants and a long-sleeve 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, people should contact their municipal government to report areas of stagnant water in roadside ditches, flooded yards and similar locations that may produce mosquitoes.

Public health officials believe that a hot summer could increase mosquito activity and the risk of disease from West Nile virus.

Additional information about West Nile virus and mosquitoes can be found on the Illinois Department of Public Health Web site at and

© 2014 Sun-Times Media, LLC. All rights reserved. This material may not be copied or distributed without permission. For more information about reprints and permissions, visit To order a reprint of this article, click here.