CHICAGO - The Chicago Department of Public Health (CDPH) is reporting Chicago's first three human cases of West Nile virus (WNV) in 2025. The patients, whose symptoms began in late July or early August, range in age from 40 to 80 years old and reside on the Northwest and South sides. The Illinois Department of Public Health previously confirmed the first human case of WNV in the state on June 24.

WNV is typically spread to humans via the bite of an infected mosquito and is not generally spread from person to person. While most people infected with WNV do not feel sick, about 1 in 5 people develop a fever and flu-like symptoms. Severe illness can occur in about 1 in 150 people and is most likely in people over age 60. Because there are no specific medications to treat WNV in people, the most effective method to prevent infection is to avoid mosquito bites.

“We are seeing a higher proportion of mosquitoes testing positive for West Nile virus than usual this year,” said CDPH Commissioner Olusimbo 'Simbo' Ige, MD, MPH. “The best way to protect yourself from West Nile virus is to avoid mosquito bites and take measures to stop them from breeding around your home.”

West Nile virus is the most common cause of mosquito-borne disease in Chicago and the United States. CDPH has a robust mosquito control program, which includes treating over 80,000 catch basins in Chicago with larvicide to kill immature mosquitoes, collecting and testing mosquitoes for WNV, and spraying in specific geographic areas to kill adult mosquitoes if needed.

CDPH has sprayed insecticide in nine different community areas over the last several weeks and will be spraying to kill adult mosquitoes in seven communities this Wednesday, August 13, 2025 (Forest Glen, Norwood Park, Mount Greenwood, and Beverly) and Thursday, August 14, 2025 (East Garfield Park, Near West Side, North Lawndale). This is the third week of spraying events to occur in the city this season.

Weather permitting, the spraying will begin at dusk on August 13 and August 14 and continue through the night until approximately 1 a.m., with licensed mosquito abatement technicians dispensing an ultra-low-volume spray from trucks. Maps of the planned spray zones can be reviewed and downloaded online:

• Wednesday, August 13: Forest Glen, Norwood Park
• Wednesday, August 13: Mount Greenwood, Beverly
• Thursday, August 14: East Garfield Park, Near West Side, North Lawndale

West Nile virus risk in Chicago is currently rated as high, and all Chicagoans are encouraged to take precautions against mosquitoes:

• Use EPA-registered insect repellant that contains ingredients such as DEET, picaridin, IR3535, or oil of lemon eucalyptus according to label instructions.
• Eliminate standing water: empty water from any outdoor containers, such as flowerpots, gutters, pet water dishes, and birdbaths on a weekly basis.
• Keep grass and weeds short to eliminate hiding places for adult mosquitoes.
• When outside between dusk and dawn, wear loose-fitting, light-colored clothing, long sleeves, pants, socks, and shoes.
• Make sure that all screens, windows, and doors are tight-fitting and free of holes.
• People who are immunocompromised should consider avoiding outdoor activity during peak mosquito hours from dusk to dawn.

For more information about mosquito levels in Chicago and mosquito-borne diseases, including symptoms and prevention, visit chicago.gov/westnilevirus. To report standing water, dead birds or high grass/weeds, call 311.

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