Media Contact:
McHenry County Department of Health
Nick Kubiak, Public Information Officer

Heavy rainfall and flooding expected to lead to increased mosquito activity

MCHENRY COUNTY, IL – The McHenry County Department of Health (MCDH) is reminding residents that recent heavy rain events and flooding are expected to lead to an increase in mosquito activity across the county.

Floodwater or nuisance mosquitoes, known as Aedes vexans, are likely to emerge in large numbers. These mosquitoes are aggressive daytime biters but are not considered significant carriers of human disease in Illinois.

In contrast, Culex mosquitoes, which are the primary carriers of West Nile virus (WNV), typically breed in stagnant water with high organic content. Common breeding sites include rimless tires, abandoned swimming pools, buckets, bird baths, and clogged gutters. The most effective way to prevent mosquito-borne illness is to eliminate standing water around homes and ensure doors and windows have tight-fitting screens.

Most people infected with WNV do not develop symptoms. However, about 1 in 5 individuals may experience mild symptoms such as headache, body aches, joint pain, vomiting, or rash. In rare cases, severe illness can occur, including high fever, neck stiffness, disorientation, tremors, muscle weakness, vision loss, paralysis, or even death. Symptoms typically develop between 2–14 days after being bitten by an infected mosquito. Adults over age 50 and individuals with certain underlying health conditions are at greater risk for severe illness. There is currently no vaccine for WNV.

MCDH begins West Nile virus surveillance in May by collecting and testing mosquito batches weekly throughout the mosquito season, which runs through October. The risk of WNV remains until the first hard frost.

Residents are encouraged to take precautions when spending time outdoors, including wearing light-colored, long-sleeved shirts and pants and applying EPA-registered insect repellents according to label instructions. Effective repellents contain one of the following active ingredients:

• DEET (N,N-diethyl-meta-toluamide)
• Picaridin (KBR 3023)
• IR3535
• Oil of lemon eucalyptus (OLE)
• Para-menthane-diol (PMD)
• 2-undecanone

Consult a healthcare provider before using insect repellent on infants. The United States Environmental Protection Agency provides a list of EPA-registered repellents; visit Find the Repellent that is Right for You.

MCDH reminds residents to follow the “3 Rs” of mosquito prevention:

• REDUCE standing water by emptying containers and maintaining proper drainage around your home.
• REPEL mosquitoes by using EPA-registered insect repellent.
• REPORT areas where stagnant water remains for more than one week.

Residents can also find flood-related safety information, cleanup guidance, and recovery resources by visiting the McHenry County Flood Information Headquarters webpage.

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