'Historic' Infection Rates Reached For West Nile Virus Mosquitoes In Area: Agency

NORTHFIELD, IL — A local agency said Friday that its surveillance is indicating "historic" infection rates among the mosquitoes that can transmit the West Nile virus in the area. North Shore Mosquito Abatement District, headquartered in Northfield, added that the Greater Chicagoland area is currently experiencing a "period of intense" WNV activity, expected to continue for another two to three weeks.

The NSMAD serves Deerfield (Cook County portion), Evanston, Glencoe, Glenview (east of Pfingsten Road), Golf, Kenilworth, Lincolnwood, Morton Grove, Niles (east of Harlem Avenue), Northbrook (east of Pfingsten Road), Northfield, Skokie, Wilmette and Winnetka.

"In early July, we enhanced our larval control treatments to further reduce adult mosquito emergence," said David Zazra, communications manager for NSMAD. "While our control efforts have kept the abundance of Culex mosquitoes low, the mosquitoes that are present are, unfortunately, more likely to be infected with WNV than in previous years."

RELATED: West Nile Virus Positive Mosquitoes Found In Northbrook — Agency

Earlier this week, the Chicago Department of Public Health reported Chicago's first three human cases of West Nile virus 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.

According to CDPH, West Nile virus is the most common cause of mosquito-borne disease in Chicago and the United States. The agency treats 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.

NSMAD is asking residents to use an EPA registered insect repellent when spending time outside — particularly during the next few weeks. Repellents containing the active ingredients Picaridin, DEET, IR3535 or Oil of Lemon Eucalyptus have been tested and proven to be safe and effective, according to NSMA. The EPA Interactive Repellent Guide on the agency's website can be used for assistance.

Additionally, NSMAD said wearing proper attire and eliminating or draining items that can hold stagnant water around local properties will help to further reduce risk.

RELATED: 1st West Nile Virus Mosquitoes Of 2025 Found In Glenview — Agency