SPRINGFIELD, IL – The Illinois Department of Public Health today announced an increase in the numbers of mosquitoes positive for West Nile virus in two areas of the state: north central Cook County and DuPage County.

"We have been closely monitoring surveillance data from local agencies and have noticed that the number of positive mosquito batches in these areas has increased since late July," said Dr. Eric E. Whitaker, state public health director. "While there have been no human cases so far this year, people should not become complacent. This elevated virus activity in the mosquito population could mean a greater risk for human disease."

Prior to July 15, Cook County had reported six positive mosquito batches. In the past month, that number has risen to a total of 33 positive mosquito batches. In DuPage County, only one positive mosquito batch had been reported prior to July 15. Since that time, nine more batches have tested positive.

"The Department intensified its surveillance efforts this year because of the outbreak that occurred last year," Dr. Whitaker said. "This has enabled us to inform the public about virus activity and the potential risk for human exposure before any human cases occur."

The Culex or house mosquito, which can carry West Nile virus or the St. Louis encephalitis virus, breeds in warm, stagnant water and increases in numbers early in the summer.

There has been less West Nile activity detected in birds and mosquitoes this year than last year, possibly because of a cool spring and summer. However, six weeks of summer remain and temperatures could increase. Higher temperatures would encourage greater Culex mosquito activity and, as a result, enhance the risk of human disease.

"While everyone in Illinois should be taking personal precautions to prevent West Nile virus disease, people who live in or near these areas need to be especially vigilant," Dr. Whitaker said.

The following common sense measures can help protect people against mosquito-borne diseases:

• Whenever outdoors between dusk and dawn or when mosquitoes are present, wear shoes and socks, long pants and a long-sleeved shirt. Loose-fitting, light colored clothing is best.
• When it is necessary to be outdoors, apply insect repellent as indicated on the repellent label. The more DEET a product contains, the longer the repellant can protect against mosquito bites. However, concentrations higher than 50 percent do not increase the length of protection. For most situations, 10 percent to 25 percent DEET is adequate. Apply repellents to clothes whenever possible; apply sparingly to exposed skin if label permits. Consult a physician before using repellents on young children.
• Check residential screens, including porches and patios, for tears and other openings and repair, as necessary, to prevent mosquito entry.
• Eliminate stagnant water in bird baths, ponds, flowerpots, wading pools, old tires and any other receptacles in which mosquitoes might breed.

WNV 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 14 days after the bite of an infected mosquito.

Dr. Whitaker said infections can be mild and include fever, headache and body aches, or can be severe and marked by headache, high fever, neck stiffness, stupor, convulsions, muscle weakness, paralysis and, rarely, death. Serious West Nile virus illness is most often present in individuals 50 years of age or older.

"Persons experiencing these symptoms should see their doctor for care," Dr. Whitaker said.

This year, a total of 29 birds, 65 mosquito batches and one horse in 25 Illinois counties have tested positive this year for West Nile virus since surveillance for the mosquito-transmitted virus began May 1.