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

Mosquitoes in McHenry County Test Positive for West Nile Virus, First of 2026

MCHENRY COUNTY, IL — The McHenry County Department of Health (MCDH) has confirmed that a mosquito pool collected from Fox River Grove on June 5, 2026, has tested positive for West Nile virus (WNV). This is the first positive mosquito test for WNV in McHenry County for the 2026 season. No human cases have been reported this year.

The MCDH will continue its WNV surveillance by collecting and testing mosquito batches throughout the season, which runs from May 1 through October 15. Residents should remember that WNV risk continues until the first hard frost. To protect themselves from mosquito-borne illness, residents are encouraged to wear protective clothing—such as light-colored, long-sleeved shirts, socks, and pants—and use EPA-registered insect repellents when outdoors.

Culex mosquitoes, the primary carriers of WNV, breed in stagnant water with high organic content, often found in manmade containers like rimless tires, abandoned swimming pools, buckets, bird baths, and clogged gutters. Eliminating standing water and ensuring doors and windows have tight-fitting screens are key steps to preventing mosquito breeding.

Most people exposed to WNV do not develop symptoms. For those who do, symptoms typically appear 2–14 days after being bitten by an infected Culex mosquito. About 20% of infected individuals may experience mild illness, including fever, headaches, body aches, joint pain, vomiting, or rash. Severe symptoms—though rare—can include high fever, headache, neck stiffness, disorientation, tremors, convulsions, muscle weakness, vision loss, numbness, and paralysis. Individuals age 50 or older or those with underlying health conditions—including diabetes, kidney disease, hypertension, cancer, or organ transplant recipients—are at higher risk of severe illness.

There is no vaccine or specific treatment for WNV. Mild symptoms may be managed with rest, fluids, and over-the-counter medications for pain or fever. Seek medical care immediately if severe symptoms develop.

EPA-registered insect repellents should contain one of the following active ingredients and be used according to label directions:

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

Consult a doctor before using repellents on infants. For a full list of EPA-registered repellents, visit the EPA's “Find the Right Repellent for You” page: https://www.epa.gov/insect-repellents/find-repellent-right-you.