Mosquitoes Test Positive For West Nile Virus

MCHENRY COUNTY, IL — A batch of mosquitoes have tested positive for West Nile virus, according to McHenry County Department of Health officials.

The health department confirmed that a mosquito pool collected from Lake in the Hills on Monday is the first batch of mosquitoes to test positive for the virus so far this year. Meanwhile, no human cases of the virus have been reported in the county, yet, in 2025.

The health department will continue its West Nile Virus surveillance by collecting and testing mosquito batches through the remainder of the mosquito season, which runs from May through October.

Residents are urged to protect themselves from mosquito-borne illnesses when outdoors by wearing protective clothing, such as light-colored, long-sleeved shirts, socks, and pants, and by using EPA-registered insect repellents, according to a news release.

Culex mosquitoes, which are the primary carriers of WNV, typically breed in stagnant water with high organic content, often found in artificial containers like rimless tires, abandoned swimming pools, buckets, bird baths, and clogged gutters. The first and best defense against mosquito-borne illnesses is to eliminate potential mosquito breeding sites by emptying standing water from containers around your home and ensuring that doors and windows have tight-fitting screens.

Most people exposed to WNV do not develop symptoms. In positive cases, however, human WNV illness typically occurs 2 to 14 days after the bite of an infected Culex mosquito.

For more information on WNV, visit www.mcdh.info or call (815) 334-4585.