McHenry County Warns After 1st 2026 West Nile-Positive Mosquito Pool Found

Q: What is the key factor that determines if a West Nile bite is a nuisance or deadly?

The deciding factor is whether West Nile virus stays a mild infection or progresses into **neuroinvasive disease**, meaning it reaches the brain or spinal cord. In most cases, a bite from an infected *Culex* mosquito is not deadly. About 80% of infected people have no symptoms, and roughly 1 in 5 develop a mild illness with fever, headache, body aches or rash. The dangerous cases are the small minority — about 1 in 150 infections — in which the virus causes encephalitis, meningitis or paralysis. That is when West Nile can become life-threatening. Who is most likely to tip into that severe category matters greatly. The McHenry County health department notes that people 50 and older, and those with conditions such as diabetes, kidney disease or cancer, face higher risk. Broader public health data also show elevated danger for people over 60, the immunocompromised, and those with chronic illnesses such as hypertension or organ-transplant-related immune suppression. So the bite itself is not what determines the outcome. The key is **how the infected person’s body responds and whether the virus invades the central nervous system**. That is why the same virus can be a nuisance for one person and deadly for another. Because there is no vaccine or specific treatment, prevention and early attention to severe symptoms remain critical.

3 articles · Updated · Lake and McHenry County Scanner · Jun 10

A mosquito pool collected Friday in Fox River Grove tested positive for West Nile virus, giving McHenry County its first confirmed sign of the virus in 2026.
No human West Nile cases have been reported in the county this year, but officials said illness can appear 2 to 14 days after an infected Culex mosquito bite.
Culex mosquitoes breed in stagnant water in places such as tires, buckets, bird baths, abandoned pools and clogged gutters, prompting the county to urge residents to drain standing water and check window and door screens.
From May through mid-October, county staff run weekly mosquito collection and testing as part of West Nile surveillance, with officials also advising long sleeves and EPA-registered repellents during dawn and dusk.