Dr. Whitaker said the woman is hospitalized with West Nile encephalitis.

The state’s other cases this year have been a 49-year-old man from Kane County with West Nile disease, a 55-year-old man from Kane County with West Nile encephalitis and a 55-year-old man from suburban Cook County with West Nile disease.

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 14 days after the bite of an infected mosquito.

Only about two persons out of 10 who are bitten by an infected mosquito will experience any illness. Illness from West Nile disease is usually mild and includes fever, headache and body aches, but serious illness, such as encephalitis and meningitis, and death are possible. Persons older than 50 years of age have the highest risk of severe disease.

The latest counties to report positive West Nile virus activity are Kendall and Winnebago. The Kendall County Health Department collected a blue jay in Yorkville on July 31 and the Winnebago County Health Department collected two positive mosquito samples in Rockford on Wednesday.

A total of four humans, 62 birds, 656 mosquito samples and one horse from 29 counties have tested positive for West Nile virus since surveillance for the mosquito-borne disease began on May 1.

In 2004, Illinois recorded 60 human cases, of West Nile disease, including four deaths, and in 2003, there were 54 human cases, including one death. The state led the nation in 2002 with 884 human cases of West Nile disease and 67 deaths.

Because West Nile virus activity in Culex mosquitoes increases during hot weather, personal protection against mosquitoes is particularly important during August and September. Dr. Whitaker said individuals can reduce their risk of West Nile illness and other mosquito-borne diseases by taking these precautions:

• 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 or oil of lemon eucalyptus 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.

Additional information about West Nile virus can be found on the Department’s Web site at www.idph.state.il.us/envhealth/wnv.htm or people can call the West Nile Virus Hotline at 866-369-9710 Monday through Friday from 8 a.m. to 5 p.m.