A mosquito pool collected from Lake in the Hills has tested positive for West Nile virus, McHenry County health department officials announced Wednesday.
The McHenry County Department of Health said in a news release that the mosquito pool was collected on Monday, June 2, marking the first positive test for West Nile virus in mosquitoes in the county during the 2025 season.
No human cases of West Nile virus have been reported in McHenry County this year, the health department states.
Culex mosquitoes, which are the primary carriers of West Nile, typically breed in stagnant water with high organic content, and are often found in artificial containers like rimless tires, abandoned swimming pools, buckets, bird baths, and clogged gutters.
Most people exposed to West Nile do not develop symptoms and there is no vaccine or treatment for West Nile virus, officials said.
Mild symptoms can be relieved with rest, fluids, and over-the-counter medications for pain and fever, and people should seek medical attention if they develop severe symptoms.
In positive cases, however, human WNV illness typically occurs 2-14 days after the bite of an infected Culex mosquito.
About 20% of those infected experience mild febrile (fever) illness with other symptoms, such as headaches, body aches, joint pains, vomiting, or a rash, officials said.
Severe symptoms are very rare and include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, and paralysis.
Individuals 50 years of age or older or those with serious underlying health conditions, such as diabetes, kidney disease, hypertension, cancer, or who have received organ transplants, are at greater risk for developing severe symptoms.
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.
The McHenry County Health Department said it will continue its WNV surveillance by collecting and testing mosquito batches through the remainder of the mosquito season, which runs from May through October.
It is important to remember that the risk of West Nile virus persists until the first hard frost.
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.
Consult with a doctor before using any repellent on infants. The United States Environmental Protection Agency (EPA) has compiled a list of EPA-registered repellents on the EPA website.
For more information on West Nile virus, people are urged to visit www.mcdh.info or call (815) 334-4585.