Mosquitos in McHenry and DuPage counties have tested positive for West Nile virus, public health officials announced.
A mosquito pool collected from Lake in the Hills on June 2 tested positive for the virus, making the pool the first mosquitoes to test positive for West Nile for the 2025 season, the McHenry County Department of Health said.
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WATCH HEREMeanwhile, in DuPage County, mosquito pools collected in Roselle, Medinah, Clarendon Hills, and Burr Ridge on May 27 also tested positive for the virus, according to the DuPage County Health Department.
No human cases have been reported so far this year in either county.
Most people exposed to the virus do not develop symptoms, though illness typically occurs two to 14 days after the bite of an infected mosquito, the department said.
“As more people begin to enjoy the outdoors during the summer season, we want them to be aware of West Nile virus and know how to protect themselves from this potentially deadly disease,” said Dr. Kiran Joshi, chief operating officer of Cook County Department of Public Health.
About 20% of those infected experience fevers, headaches, body aches, joint pains, vomiting, or a rash, health officials said. Severe symptoms are “very rare” and include neck stiffness, coma, muscle weakness, vision loss, numbness, and paralysis.
Anyone 50 years old and older or with underlying health conditions like diabetes, kidney disease, hypertension or cancer are more at risk at developing severe symptoms, according to the department.
Though there is no vaccine or treatment for the virus, mild symptoms can be relieved with rest, fluids and over-the-counter medication, officials said.
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SIGN UP The department will continue to collect and test mosquito batches through the remainder of the mosquito season, which runs from May through October.
McHenry County residents are urged to wear protective clothing outside like light-colored, long-sleeved shirts, socks and pants, health officials said. Residents are also urged to use EPA-registered insect repellents.
Culex mosquitoes, which are the primary carriers of the virus, typically breed in motionless water with high organic content, often found in artificial containers like rimless tires, abandoned swimming pools, buckets, bird baths, and clogged gutters, according to the department.
The best defense against mosquito-borne illnesses is to empty standing water from containers around your home and ensure that doors and windows have tight-fitting screens, therefore eliminating potential mosquito breeding sites, the department added.
In 2024, suburban Cook County saw 19 West Nile virus cases and five deaths due to the virus — marking the highest number of county deaths due to the disease since 2018, according to Cook County Department of Public Health data.
In all of Illinois last year, 69 people were confirmed to have the virus and 13 West Nile deaths were reported, officials said.
For more information on the West Nile virus, visit www.mcdh.info and FightTheBiteCookCounty.com.
