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What is West Nile Virus (WNV)?

West Nile virus is a serious disease most commonly spread by infected mosquitoes. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the virus to humans and other animals. Symptoms (see below) are usually mild, but in rare cases, severe illness including encephalitis (inflammation of the brain), meningitis (inflammation of the lining of the brain and spinal cord), or even death, can occur.

Where is West Nile Virus found?

In North America, cases of WNV occur during mosquito season, which starts in the summer and continues through fall. WNV cases have been reported in all of the continental United States. Surveillance for West Nile virus in Illinois includes laboratory tests on mosquitoes, dead crows, blue jays, robins and other perching birds, as well as sick horses and humans with WNV-like symptoms. Surveillance for WNV in mosquitoes involves placing traps that attract and collect the mosquitoes that carry WNV. Mosquitoes are then tested for the presence of WNV in a laboratory. Mosquito surveillance data in suburban Cook County comes from the Cook County Department of Public Health (CCDPH), Northwest Mosquito Abatement District, North Shore Mosquito Abatement District, Desplaines Valley Mosquito Abatement District, South Cook County Mosquito Abatement District, and the Illinois Department of Public Health. Click here to view the latest weekly surveillance data showing where WNV is circulating in suburban Cook County. This report serves as the official statement of West Nile Virus activity in humans, mosquitoes, and birds within the jurisdiction of the Cook County Department of Public Health. Click here to view all WNV surveillance reports.

CCDPH responds to complaints of unmaintained private residential pools and standing water within suburban Cook County and unincorporated areas of Cook County (excluding Chicago, Oak Park, Stickney Township, Evanston and Skokie). To report concerns about standing water, you may: contact the mosquito abatement district where you live, call the CCDPH West Nile virus Hotline at 708-633-8025, or submit an online complaint form. Contact the Chicago Department of Public Health for complaints in Chicago.

Who is most at risk for West Nile Virus?

Anyone living in an area where West Nile virus is present in mosquitoes can get infected. Serious illness can occur in people of any age. However, those at greatest risk are people that: are over 50 years of age; have certain medical conditions, such as cancer, diabetes, hypertension, kidney disease; have received organ transplants; and/or spend a lot of time outdoors; especially between dusk and dawn.


What are the symptoms?

1Common symptoms : fever, nausea, headache and muscle aches.

2Severe symptoms : High fever, stiff neck, confusion, and muscle weakness

What to do if you are experiencing symptoms

Symptoms may last from a few days to a few weeks. Contact your primary healthcare provider if you are experiencing WNV symptoms.