First West Nile Virus-Positive Mosquitoes Found In Riverwoods

The North Shore Mosquito Abatement District said infection risk remains low but is increasing.

By Eric DeGrechie, Patch Staff

Aug 5, 2026 9:47 AM CDT | Updated Aug 5, 2026 10:05 AM CDT

RIVERWOODS, IL — The first West Nile virus-positive mosquitoes of the year have been detected in Riverwoods, according to the North Shore Mosquito Abatement District.

One batch collected Aug. 3 from an NSMAD trap in Riverwoods tested positive in the district's laboratory Aug. 4.

West Nile virus-positive mosquitoes have now been detected in every community served by the mosquito abatement district this year, officials said.

The latest finding follows earlier positive mosquito tests in several North Shore communities, including Deerfield and Northbrook. Northbrook's first positive batch was collected June 8, while the first Deerfield batch was collected July 1.

Infection Risk Increasing

The district said the current risk of becoming infected with West Nile virus remains low but is increasing.

West Nile virus is most commonly transmitted to people through the bite of an infected mosquito. There is no licensed vaccine or preventive medication for people, making avoidance of mosquito bites the primary protection against infection.

NSMAD recommends that residents:

Use an EPA-registered insect repellent while outdoors.
Wear loose-fitting clothing that covers exposed skin.
Avoid spending time outside around dawn and dusk, when mosquitoes that transmit West Nile virus are most active.
Examine their property and remove standing water from containers and other items.

Residents should empty, scrub, cover or discard water-holding objects such as buckets, toys, birdbaths, flowerpot saucers and trash containers at least once a week, according to the Centers for Disease Control and Prevention.

"If it can hold water, it can breed mosquitoes," the district said.

Residents experiencing mosquito-related problems can contact NSMAD for assistance. Current mosquito-testing results are available through the district's Mosquito Surveillance Dashboard.